Dissertations / Theses on the topic 'Contrast sensitivity (Vision)'

Thesis (doctoral)--Technische Universiteit Eindhoven, 1999.
"SPIE digital library." Originally published: Knegsel : HV Press, 1999. Includes bibliographical references and index. Also available in print version.

Early visual processing is subject to binocular interactions because cells in striate cortex show binocular responses and ocular dominance (Hubel & Weisel, 1968). The work presented in this thesis suggests that these physiological interactions can be revealed in psychophysical experiments using normal human observers. In the region corresponding to the blind spot, where binocular interactions differ from areas of the visual field which are represented by two eyes, monocular contrast sensitivity is increased. This finding can be partially explained by an absence of normal binocular interactions in this location (Chapter 2). A hemianopic patient was studied in an attempt to discover whether the effect in normal observers was mediated by either a mechanism in striate cortex or via a subcortical pathway. However, the results were unable to distinguish between these two explanations (Chapter 3).In a visual search task, no difference in reaction time was observed for targets presented to the region corresponding to the blind spot compared with targets presented to adjacent binocularly represented areas of the visual field. Since performance was unaffected by the monocularity of the region corresponding to the blind, pop-out for orientation may be mediated beyond striate cortex where cells are binocularly balanced (Chapter 5). Further support for this contention was provided by studies of orientation pop-out in central vision which found that dichoptic presentation of stimuli did not affect the degree of pop-out obtained and that in general, visual search for a target based solely on eye of origin is impossible (Chapter 6). However, a task that measured orientation difference sensitivity more directly than the search experiments, found that thresholds were higher for dichoptically presented stimuli. This suggests the involvement of neurons that receive a weighted input from each eye. A model of orientation difference coding can account for the results by assuming that the range of inhibition across which orientation differences are coded is narrower for dichoptic stimuli leading to a greater resolvable orientation difference (Chapter 7).

This study involved the determination of the effects of binocular viewing on contrast sensitivities in 11 normal subjects and in different categories of amblyopes. These were simple anisometropic amblyopes (n=9), micro-esotropic amblyopes with anomalous BSV (n=6), esotropic amblyopes with anomalous BSV (n=3) esotropic without BSV 9n=5), exotropic amblyopes without BSV (n=2) and a group of non-amblyopic strabismics (non-amblyopic esotropes without BSV (n=4); non-amblyopic exotropes without BSV (n=2).An ophthalmic examination was carried out on all individuals. The examination procedures undertaken comprised determination of the visual acuity, subjective refraction, the results of which were confirmed by retinoscopy, and assessment of uniocular fixation patterns. The state of BSV, the direction and magnitude of the angle of deviation, the amplitude of accommodation and pupillary diameter were also determined. The subjects were accordingly placed into the appropriate groups on the basis of the basis of the results of the ophthalmic examination. Measurement of uniocular and binocular contrast sensitivities in response to stationary vertical sinusoidal grating patterns were undertaken. The stimulus display consisted of a Tektronix 5103 cathode ray tube (CRT) with a screen subtense of 2 degrees. Mean contrast threshold values were measured for monocular and binocular viewing over the range of spatial frequencies studied which varied between 8c/deg to 40c/deg depending on the group being examined. The conclusions reached were, first, in individuals with BSV (normal or anomalous), binocular enhancement of contrast sensitivities occurred. However, strabismic amblyopes without BSV and non-amblyopic strabismics without BSV did not exhibit enhanced binocular contrast sensitivities; on the contrary, binocular contrast sensitivities were reduced compared to those obtained through the better eye. Furthermore, when bifoveal stimulation was effected, a further reduction in binocular contrast sensitivity occurred. This study has thus shown that binocular contrast sensitivities are augmented compared with monocular contrast sensitivities when BSV is present, but are decreased when BSV is absent. Furthermore, correction of the angle of squint in strabismics, whether BSV is present or not, further reduces the binocular contrast sensitivities.

Contrast sensitivities to one- and two-dimensional luminance patterns were compared in a two-alternative forced choice (2AFC) experiment. Space-averaged luminance was also manipulated. Statistical analyses revealed a main effect of stimulus dimension (p < .05) and no effect of space-averaged luminance. The main effect of stimulus dimension was explained in terms of an on-center, off-center receptive field model combined with watershed spatial vision behavior at spatial frequencies below 1 cycle-per-degree (cpd). The non-significant result for space-averaged luminance was explained by the limited range of manipulation of the variable. Two-dimensional luminance patterns were suggested as ideal patterns for reconciling grating-based spatial vision research with spatial vision behavior in an ecological context. Future research directions are suggested.
Master of Science

It has long been held that luminance acts as a cue for depth perception. But varying the luminance of a stimulus inevitably alters its contrast with its background. Recent research shows that contrast is a depth cue. I have distinguished two kinds of contrast, external contrast, the contrast of a stimulus with its background, and internal contrast, the contrast within the stimulus. I compared the relative apparent depth of two stimuli (both directly and indirectly; stimuli were either sine-wave filled hemifields, sine-wave filled squares, or plain squares), as their luminances and internal contrasts were varied along with the luminance of their background. I found internal and external contrast to be additive effects, whereby the stimulus with either a higher internal or external contrast appeared nearer. When the internal and external contrasts of the stimuli were equated, luminance acted as an ambiguous cue, with the lighter square appearing nearer for the majority of observers, and farther for a minority. Luminance may act as a depth cues from our experience with artificial lighting (artificial light varies ambiguously with depth). Contrast may act as a depth cue from its usual association with the reduction of contrast of objects with distance through the atmosphere. I conclude that luminance and contrast are independent depth-cues that are caused by two different mechanisms.

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains xi, 101 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 95-99).

The loss of central vision subsequent to macular disease is often extremely debilitating. People with central field loss (CFL) must use other peripheral areas of the retina in order to see; areas with inferior resolution capacity, which are also affected by off-axis optical errors. The overall aim of the work encompassed by this thesis was to identify and evaluate methods of improving vision for people with CFL; with focus on the effects of off-axis optical correction and stimulus motion on resolution acuity and contrast sensitivity. Off-axis optical errors were measured using a commercially-available COAS-HD VR open-view aberrometer. We used adaptive psychophysical methods to evaluate grating resolution acuity and contrast sensitivity in the peripheral visual field; drifting gratings were employed to   measure the effect of motion on these two measures of visual performance. The effect of sphero-cylindrical correction and stimulus motion on visual performance in healthy eyes and in subjects with CFL was also studied; in addition, the effect of adaptive optics aberration correction was examined in one subject with CFL. The COAS-HD aberrometer provided rapid and reliable measurements of off-axis refractive errors. Correction of these errors gave improvements in low-contrast resolution acuity in subjects with higher amounts of oblique astigmatism. Optical correction also improved high-contrast resolution acuity in most subjects with CFL, but not for healthy subjects. Adaptive optics correction improved both high and low contrast resolution acuity in the preferred retinal locus of a subject with CFL. The effect of stimulus motion depended on spatial frequency; motion of 7.5 Hz improved contrast sensitivity for stimuli of low spatial frequency in healthy and CFL subjects. Motion of 15 Hz had little effect on contrast sensitivity for low spatial frequency but resulted in reduced contrast sensitivity for higher spatial frequencies in healthy subjects. Finally, high-contrast resolution acuity was relatively insensitive to stimulus motion in the periphery. This thesis has served to broaden the knowledge regarding peripheral optical errors, stimulus motion and their effects on visual function, both in healthy subjects and in people with CFL. Overall it has shown that correction of off-axis refractive errors is important for optimizing peripheral vision in subjects with CFL; the use of an open-view aberrometer simplifies the determination of these errors. In addition, moderate stimulus motion can have a beneficial effect on contrast sensitivity for objects of predominantly low spatial frequency.

Objetivo: Avaliar a Função de Sensibilidade ao Contraste de Luminância Espacial e Temporal, estudar o desenvolvimento destas funções, a contribuição das vias de processamento paralelo para as funções de Sensibilidade ao Contraste e seu respectivo desenvolvimento e, por fim, determinar valores normativos destas funções visando uma aplicabilidade clínica.Método A avaliação psicofísica de sensibilidade ao contraste de luminância espacial e temporal foi realizada em 112 sujeitos divididos em três grupos:GrupoI ( idade média =9,14±2,7 anos),Grupo II ( idade média=23,7 ± 3,4 anos) e Grupo III ( idade média=41,8± 5,5 anos) com o programa PSYCHO for Windows Versão 2.36 (Cambridge Research Systems, CRS-Ltd, UK) acoplado a um microcomputador PC XTC -600. . Os estímulos foram apresentados em um monitor Sony Triniton de 19 polegadas GFD420 (Sony Corporation, USA) com resolução espacial de 800X600 e resolução temporal de 69 Hz Os estímulos eram comandados pela placa gráfica VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Resultados A avaliação psicofísica para a sensibilidade ao contraste espacial e temporal mostraram que esta função já está desenvolvida e em pleno funcionamento em crianças (6 anos) ocorrendo um declínio para as frequências espaciais de 2,0cpg;8,3cpg e 14,5cpg para os grupos II e III.Para a frequência temporal de 2,5Hz o declínio ocorre nos Grupos II e III e para a frequência temporal de 5,0 Hz nas idades mais avançadas(GIII). Para o estudo da contribuição das vias de processamento paralelo (magnocelular e parvocelular) podemos notar uma maior sensibilidade ao contraste para decremento de luz do que para incremento de luz, porém não foi possível determinar a real contribuição dessas vias para a função de sensibilidade ao contraste. Conclusão Avaliamos com sucesso a Sensibilidade ao Contraste Espacial e Temporal para todas as faixas etárias e, assim, conseguimos ter acesso ao desenvolvimento desta função, entre as idades de 6 e 57 anos. Valores normativos para as tais funções foram estabelecidos por metodologia nãoparamétrica.. O estudo da contribuição das vias magnocelular e parvocelular não pode ser conclusivo, porém os achados mostraram uma maior sensibilidade para o decremente de luz o que corrobora com a literatura
Purpose: To analyze the spatial and temporal luminance contrast sensitivity function, to study the development of these functions, the contribution of the parallel processing pathways and to determine the normative values of these functions to order a clinical applicability normative. Methods the psychophysical evaluation of the spatial and temporal luminance contrast sensitivity was performed in 112 subjects divided into three groups: Group I (mean age =9.14±2.7 years), Group II (mean age=23.7 ± 3.4 years) and Group III (mean age=41.8± 5.5 years) with the PSYCHO for Windows Version 2.36 (Cambridge Research Systems, CRS-Ltd, UK) connect to the microcomputer PC XTC -600. The stimuli was showed in a monitor Sony Triniton de 19 inches GFD420 (Sony Corporation, USA) with spatial resolution of the 800X600 and temporal resolution of the 69 Hz. The stimuli was made by the graphics card VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Results The psychophysics evaluation to spatial and temporal contrast sensitivity showed that this function is already developed and full operation in children (6 years old) with a decline to spatial frequencies of 2.0cpg;8.3cpg and 14.5 cpg to the groups II and III. For the temporal frequency of 2.5Hz the decline occur to the groups II and III .and to the temporal frequency of 5.0 Hz the decline occur to the advantage ages(GIII). For the study of the parallel processing pathways (magnocellular e parvocellular) we can see bigger contrast sensitivity to decrement than to increment of light. It was not possible determine the real contribution of these pathways to the contrast sensitivity function. Conclusion We evaluated in a successful way the spatial and temporal contrast sensitivity to all age range and so we could access the development of this function between the ages from 6 to 57 years old. Normatives values to this function were established for non parametric methodology. The study of the contribution of the parvocellular and magnocellular pathways is not conclusive, but the results showed a bigger sensibility to decrement than to increment of light that was similar to the literature

For many older adults, night driving is difficult due to age-related changes affecting vision under low light and glare conditions. However, there is a lack of evidence for healthcare practitioners to base their advice to patients about visual fitness to drive safely at night. This research investigated the relationships between self-reported vision-related night driving difficulties, visual function tests and night driving performance. It was found that vision tests conducted under lower light levels, similar to the night driving environment, were important for predicting poorer night driving performance and for assessing drivers reporting high levels of vision-related night driving difficulties.

Visual field testing, or perimetry, measures peripheral visual loss in eye diseases such as glaucoma. Rarebit Perimetry (RBP) is a new and novel perimetric method, introduced in 2002 by Lars Frisén (2002), with the aim of detecting low degrees of neural damage within the retina.
RBP is unlike conventional perimetric methods that measure levels of retinal sensitivity, but instead uses very bright (i.e. suprathreshold) and very small targets to detect tiny areas of absolute blindness within otherwise normal areas of vision. RBP thus claims to locate miniscule gaps in the receptive field matrix of neurons in the retina, with the assumption that dead neurons leave gaps in this matrix. The most useful application of this idea is to detect progressive eye disease in the earliest stages (Frisén, 2002). Current research shows that RBP correlates with other standard visual field tests (Brusini, Salvetat, et al., 2005; Frisén, 2003; Gedik, Akman, et al., 2007; Martin & Wanger, 2004), but may afford greater sensitivity by detecting very mild visual losses missed by other tests (Martin, Ley, et al., 2004; Martin & Nilsson, 2007; Nilsson, Wendt, et al., 2007).
To date, there are no studies that definitively test the theoretical basis of RBP, so in this thesis I aim to explore the proposed underlying mechanisms and assumptions of this test. In particular, the proposed mechanism of RBP leads to specific predictions as to how responses will alter when the luminances of the RBP targets are systematically decreased. I therefore compared RBP responses of mean hit rate as a function of target luminance and found results to be inconsistent with the proposed RBP mechanism. Mathematical simulations were performed to explore reasons for the differences between the two groups (Chapter Seven).

Color and luminance perception both rely on the different combinations of the three cone types, termed L, M, and S cones. Each of the color opponent mechanisms can be defined by their cone weights with (L-M) for Red-Green, (S-0.5(L+M)) for Blue-Yellow, and (2L+M) for the luminance mechanism.
My project investigates two aspects of peripheral color vision. One looks at the spatial summation of the three mechanisms across eccentricity and the other one looks at the selective loss of red-green cone contrast sensitivity in the periphery.
In the spatial summation experiment, we have used two kinds of horizontal gratings for the investigation: a gabor patch and a sine wave ring stimulus. A gabor patch is a conventional visual research stimulus. A radially modulated sine wave ring stimulus is one we designed to test peripheral vision with the advantage of confining its spatial position in eccentric location. In other words, from changing the radius of the ring, we can place the rim of the ring either nearer or further in eccentricity from the central point. Our results show three things: the spatial summation of both chromatic mechanisms and luminance mechanism are similar, spatial summation for all three mechanisms varies across eccentricity, and lastly we find that spatial summation is constant in spatial extent as opposed to the number of spatial cycles. This last finding is in contradiction to previous results, which have found that the spatial summation of the luminance mechanism is determined by the number of stimulus cycles rather than its spatial extent.
We used the sine wave ring stimulus, as described in the spatial summation experiment, for our second investigation. Our results show that red-green mechanism unlike the other two mechanisms has a steep post-receptoral signal loss in the periphery, using the sine wave ring confirming previous studies. In addition, we have found the outer bound limit of red-green peripheral perception occurs at around 25 to 30 degree. We have optimally increased the stimulus in size and in contrast, but the red-green detection limit cannot be eccentrically set further.

Considerable evidence indicates that visual sensitivity is reduced during saccadic eye movement. A central question has been whether saccadic suppression results from a non-visual central signal, or whether the obligate image motion that accompanies saccades is itself sufficient to mask vision. In the first of a series of experiments described here, the visual and non-visual effects of saccades were distinguished by measuring contrast sensitivity to luminance modulated low spatial frequency gratings, at 17 cd·m¯² and 0.17 cd·m¯², in saccade conditions and in conditions in which saccade-like image motion was produced by the rotation of a mirror but when observers’ eyes were kept still. The time course of suppression was examined by making measurements from well before image motion began until well after it had ended. A tenfold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high contrast noise to the visual display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades. At lower luminance, suppression was found to be reduced, and its course shallower than at higher luminance. Simulated saccades produced shallower suppression over a longer time course at both higher and lower luminance. In a second experiment the time course of contrast sensitivity to chromatically modulated gratings, at 17 cd·m¯², was examined. No suppression was found; rather there was some evidence of an enhancement of sensitivity, both before and after saccades, relative to fixation conditions. Differences in the effects of real and simulated saccades in the magnitude and time course of sensitivity loss with luminance modulated gratings suggest that saccadic suppression has an extraretinal component that acts on the magnocellular system; the pattern of enhancement found in the later experiment suggests a selective favouring of the parvocellular system both immediately prior to and immediately after saccades. The possibility that the degree of enhancement in sensitivity varies across the visual field was examined using spatially localized stimuli (either high spatial frequency chromatically modulated gratings or letter combinations). Sensitivity was found to decrease at the initial fixation point during the 75 ms prior to saccadic onset and simultaneously to improve at the saccadic target. In the immediate post-saccadic period, sensitivity at the saccadic target was found to exceed that which had been manifest at the initial fixation point prior to saccades, suggesting that post-saccadic enhancement may improve the temporal contrast between one fixation and the next. The final experiments investigated the possibility that our sense of continuity across saccades (as opposed to stability) is influenced by saccade-induced errors in locating events in time. The results of these experiments suggest that saccades can result in errors in judging (a) the time at which external events occur relative to saccadic onset, (b) the temporal order of visual events, and (c) the magnitude of temporal intervals. It is concluded that apparent time is generally foreshortened prior to saccades. This might be due to selective suppression of magnocellular activity and might function to hide saccades and their effects from our awareness. A speculative synthesis is presented based on the idea that recurrent feedback between the neocortical and cortical structures on the one hand, and the thalamic nuclei on the other, has special importance for perception around the time of saccades

This research is about evaluating vision in the periphery. Peripheral vision is of fundamental importance in the performance of our everyday activities. The aim of this thesis is to develop methods suitable for the evaluation of peripheral vision and to assess how different visual functions vary across the visual field. The results have application both within the field of visual rehabilitation of people with central visual field loss (CFL)and as well as in myopia research. All methods for assessing peripheral vision were implemented with adaptive psychophysical algorithms based on Bayesian statistics. A routine for time-efficient evaluation of peripheral contrast sensitivity was implemented and verified for measurements out to 30° in the visual field. Peripheral vision was evaluated for different properties of the stimuli: sharpness, motion, orientation, and extent. Optical quality was controlled using adaptive optics and/or corrective spectacles specially adapted for the peripheral viewing angle. We found that many peripheral visual functions improved with optical correction, especially in people with CFL. We also found improvements in peripheral contrast sensitivity for low spatial frequencies when stimuli drifted at 5 to 10 Hz; this applies both for people with normal vision and those with CFL. In the periphery, it is easier to see lines that are oriented parallel with respect to the visual field meridian. We have shown that this directional bias is present for both resolution and detection tasks in the periphery, even when the asymmetric optical errors are minimized. For accurate evaluation of peripheral vision, we therefore recommend using gratings that are oriented oblique to the visual  field meridian. The directional bias may have implications in how peripheral image quality affects myopia progression. Another proof that peripheral vision can influence central visual function is the fact that, when the stimulus extent was increased beyond the fovea, the blur in the stimulus was less noticeable.
Denna forskning handlar om att utvärdera synen i periferin. Vår perifera syn är ovärderlig i det dagliga livet. Målsättningen med denna avhandling är dels att utveckla metoder speciellt lämpade för perifer synutvärdering och dels att mäta hur olika synfunktioner varierar över synfältet. Resultaten har tillämpning både inom synrehabilitering för personer med centraltsynfältsbortfall och inom närsynthetsforskning. Adaptiv psykofysisk metodologi baserad på Bayesiansk statistik användes vid all utvärdering av det perifera seendet. Vi implementerade en rutin för tidseffektiv mätning av perifer kontrastkänslighet och verifierade den ut till 30° i synfältet. Den perifera synen utvärderades för olika egenskaper hos objektet: skärpa, rörelse, riktning och utbredning. Skärpan kontrollerades med hjälp av adaptiv optik och/eller glasögonkorrektion speciellt anpassad för den perifera synvinkeln. Vi fann att många periferasynfunktioner förbättras av optisk korrektion, särskilt för personer med centralt synfältsbortfall. Vi hittade även förbättringar i periferkontrastkänslighet för låga ortsfrekvenser när objektet modulerades med hastigheter mellan 5 och 10 Hz, vilket gäller både normalseende och personer med centralt synfältsbortfall. I periferin är det lättare att se linjer som är orienterade parallellt med synfältsmeridianen. Vi har visat att denna riktningsbias gäller både för upplösning och detektion i periferin, även när de asymmetriska optiska felen minimeras. För bästa mätnoggrannhet rekommenderar vi därför att använda randmönster som ligger snett relativt synfältsmeridianen. Denna riktningsbias skulle även kunna påverka hur den perifera bildkvalitén inverkar på utvecklingen av närsynthet. Ytterligare ett bevis för att perifer syn kan påverka den centrala synfunktionen är att, när objektets utbredning ökades, uppfattade personen det som mindre suddigt.

QC 20160826

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Workers chronically exposed to a variety of organic solvents may suffer from changes in color vision and contrast sensitivity (CS). However, few studies have investigated whether there are sex-related differences in these changes, one of the factors that can change the toxicokinetics of solvents. Hence, the aim of this study was to determine whether there would be differences between women and men exposed in terms of their chromatic and achromatic visual psychophysical responses. A total of 44 individuals, Control Group total (CGt; n = 22) and Study Group total (SGt; n = 22) participated in the experiment, subdivided into the following groups: Study Group men (SGm): 11 men exposed to solvents (Age, M = 30.18, SD = 6.48; Education level, M = 9.73, SD = 2.10; Work duration, M = 6.53, SD = 4.38); Study Group women (SGw): 11 women exposed to solvents (Age, M = 26.91, SD = 5.86; Education level, M = 10, 36, SD = 0.92; Work duration, M = 4.70, SD = 3.53); Control Group men (CGm): 11 unexposed men (Age, M = 26.73, SD = 6.5; Education level, M = 9.73; SD = 1.8); Control Group women (CGm): 11 unexposed women (Age, M = 26.55, SD = 6.5; Education level, M = 10.45; SD = 1.51). The project was approved by the Ethics Committee of the Health Sciences Center (SCC) at the Federal University of Paraíba (UFPB), with CAAE registry number 21350113.9.0000.5188. Initially the participants underwent a screening step, with the following inclusion criteria, among others: a 20/20 or corrected visual acuity (evaluated via optotypes and Rasquin testing) and no dyschromatopsia (evaluated using Ishirara Test). Assessment of color perception was performed using the D15 desaturated Lanthony test (D15d) and the Cambridge Colour Test (CCT). The evaluation was performed by CS stimulation using sinusoidal gratings with a vertical spatial frequency of 0.2, 0.5, 1.0, 2.0, 5.0, 10, and 16 cycles per degree (cpd) of visual angle. Furthermore, an assessment of body composition from an examination of bioimpedance. The data were analyzed using the SPSS software package, version 21. First, the overall results between the SGt group (n = 22) and CGt group (n = 22) were compared, and were subsequently compared by sex (n = 11). The results showed that the study group (SGt) (Mdn = 1.18; M = 1.31, SD = 0.32) had a significantly higher ICC (U = 128, p = 0.01) than the CGt (Mdn = 1.09; M = 1.10, SD = 0.26), while there were no significant differences between solvent-exposed men and women (U = 51.0, p = 0.53). In CCT testing (Trivector Protocol), the SGt had a length corresponding to the vector protan axis (Mdn = 50.00; M = 54.00, SD = 16.42), and was significantly higher (U = 133.50, p = 0, 01) than the combined CGt group (Mdn = 40.00; M = 42.59, SD = 16.42), while according to the ellipse protocol, the SGt (Mdn = 981.15; M = 8086.81 ; SD = 22787.81) had a significantly higher ellipse area in A3 (U = 158.00, p = 0.04) compared to the CGt (Mdn = 657.30; M = 781.75, SD = 528.68), but men and women showed no significant differences in both CCT protocols (p > 0,05). The results of the CS showed that the SGt had lower CS in the following frequencies: 0.2 (U = 116,500, p = 0.003); 0.5 (U = 117.00, p = 0.003); 5.0 (U = 149.50, p = 0.03) and 10 cpd (U = 150.00, p = 0.03) compared to the CGt. The SGm (U = 25.0, p = 0.02) had significantly higher CS than SGm at the 0.5 cpd frequency value. The correlational analyses showed that among SGw, the diameter values of circles equivalent to the A1 and A2 ellipse areas retained a significant correlation with MCM: ρ = -0.68; p = 0.02 and ρ = -0.83; p = 0.01, respectively. Among SGw, the diameter value of the circle equivalent to the A2 area was negatively correlated with fat mass: ρ = -0.67; p = 0.02, in other words a greater amount of fatty tissue was correlated with a lower error trend in the red-green opponency axis, in addition, the diameter value of the circle equivalent to the A3 area had a positive correlation with MCM: ρ = 0.61; p = 0.04, i.e. a greater amount of MCM was correlated with a greater tendency to error in the color opponency axis. In short, the data on color vision and the SC obtained by solvent-exposed women and men found no strong evidence of possible differences between the sexes. However, the associations of psychophysiological measurements with the body measurements seem to indicate that fat can act as a protective factor of the organism against the effects of solvents, since fatty tissues may retain a proportion of solvents. In this regard, women could be less affected by solvents by having, on average, a larger proportion of adipose tissue than men.
Trabalhadores expostos de forma crônica à mistura de solventes orgânicos podem sofrer alterações na visão de cores e na sensibilidade ao contraste (SC). Entretanto, poucos estudos investigaram se há diferenças entre os sexos, um dos fatores que podem alterar a toxicocinética dos solventes. Diante disto, o objetivo do presente estudo foi verificar se haveria diferença entre mulheres e homens expostos quanto as respostas psicofísicas visuais cromáticas e acromáticas. Participaram 44 pessoas, Grupo de Estudo total (GEt; n = 22) e Grupo Controle total (GCt; n = 22) que formaram os seguintes grupos: Grupo de Estudo Homens (GEh): 11 homens expostos (Idade M = 30,18; DP = 6,48; Escolaridade M = 9,73; DP = 2,10; Tempo de serviço M = 6,53; DP = 4,38); Grupo de Estudo Mulheres (GEh): 11 mulheres expostas (Idade M = 26,91; DP = 5,86; Escolaridade M = 10, 36; DP = 0,92; Tempo de serviço M = 4,70; DP = 3,53); Grupo Controle Homens (GCh): 11 homens não expostos (Idade M = 26,73; DP = 6,5; Escolaridade M = 9,73; DP = 1,8); Grupo Controle Mulheres (GCm): 11 mulheres não expostas (Idade M = 26,55; DP = 6,5; Escolaridade M = 10,45; DP = 1,51). O projeto foi aprovado pelo Comitê de Ética do Centro de Ciências da Saúde (CCS) da Universidade Federal da Paraíba (UFPB), com número de CAAE: 21350113.9.0000.5188. Inicialmente os participantes realizaram uma de triagem, permanecendo aqueles que, entre outros critérios, apresentaram acuidade visual 20/20 ou corrigida (Optotipos E de Rasquin) e ausência de discromatopsias congênitas (Teste de Ishirara). A avaliação da percepção cromática foi realizada por meio dos testes D15 Dessaturado de Lanthony (D15d) e Cambridge Colour Test (CCT). A avaliação da SC foi realizada com estímulos de grades senoidais verticais de frequências espaciais de 0,2; 0,5; 1,0; 2,0; 5,0; 10 e 16 cpg de ângulo visual. Ainda foi realizada uma avaliação da composição corporal a partir de um exame de biompedância. Os dados foram analisados por meio do software SPSS, versão 21. Primeiramente, foram comparados os resultados entre o GEt (n = 22) e o GCt (n = 22), em seguida os resultados foram comparados por sexo (n = 11). Os resultados mostraram que o GEt apresentou ICC (Mdn = 1,18; M = 1,31; DP = 0,32) significativamente maior (U = 128; p = 0,01) ao GC (Mdn = 1,09; M = 1,10; DP = 0,26), ao passo que entre mulheres e homens expostos não houve diferenças (U = 51,0; p = 0,53). Com relação ao CCT, Protocolo Trivector, o GEt apresentou comprimento correspondente ao vetor do eixo protan (Mdn = 50,00; M = 54,00; DP = 16,42) significativamente maior (U = 133,50; p = 0,01) que o GC (Mdn = 40,00; M = 42,59; DP = 16,42), já no Protocolo Elipse, o GEt obteve área da elipse A3 (Mdn = 981,15; M = 8086,81; DP = 22787,81) significativamente maior (U = 158,00; p = 0,04) em relação ao GCt (Mdn = 657,30; M = 781,75; DP = 528,68), mas homens e mulheres não apresentaram diferenças em ambos os protocolos do CCT (p > 0,05).. Os resultados da SC mostraram que o GEt apresentou SC menor nas frequências: 0,2 (U = 116,50; p = 0,003); 0,5 (U = 117,00; p = 0,003); 5,0 (U = 149,50; p = 0,03) e 10 cpg (U = 150,00; p = 0,03) comparado ao GCt. O GEm obtive SC significativamente maior (U = 26,0; p 0,02) que o GEh na frequência 0,5 cpg. As análises correlacionais evidenciaram que entre o GEh, os valores dos diâmetros dos círculos equivalentes as áreas das elipses A1 e A2 mantiveram correlação com a MCM: = -0,68; p = 0,02 e = -0,83; p = 0,01, respectivamente. Já entre o GEm o valor do diâmetro do círculo equivalente a área A2 apresentou correlação negativa com a massa de gordura: = -0,67; p = 0,02, ou seja quanto mais gordura, menor tendência de erro no eixo de oponência de cor vermelho-verde, e ainda o valor do diâmetro do círculo equivalente a área A3 obteve correlação positiva com a MCM: = 0,61; p = 0,04, isto é quanto maior a quantidade de MCM, maior tendência de erro no eixo de oponência de cor. Em suma, os dados relativos à visão de cores e a SC obtidos por mulheres e homens expostos não encontraram fortes evidências de possíveis diferenças entre os sexos. Entretanto, as associações das medidas psicofísicas com as medidas corporais parecem indicar que a gordura pode atuar como um fator de proteção do organismo contra os efeitos dos solventes, já que tecidos gordurosos podem reter produto. Nesta perspectiva, as mulheres poderiam ser menos afetadas por apresentarem quantidade maior de tecido adiposo.

O presente estudo investigou a função visual de pacientes com diabetes tipo 1 atletas e sedentários através de testes psicofísicos e eletrofisiológicos computadorizados de última geração. O objetivo foi investigar possíveis efeitos do exercício físico nas funções visuais. Materiais e Métodos: 33 pacientes com diabetes tipo 1, divididos em dois grupos experimentais: diabético atleta (n = 15; idade = 33,33 ± 6,78; tempo de doença =16,19 ± 6,63) e diabéticos sedentário (n = 18 idade = 28,94 ± 6,04; tempo de doença = 15,92 ± 8,46) e 40 sujeitos controles: controle atleta (n = 20; idade = 32,0 ± 5,61) e controle sedentário ( n = 20; idade = 27,05 5,60 ) foram submetidos a exames de: visão de cores e sensibilidade ao contraste Cambridge Colour Test - CCT; eletroretinograma por padrão reverso PERG e análises laboratoriais para quantificar óxido nítrico e endotelina por quimioluminescência e ELISA. As comparações entre os grupos foram feitas através de teste não paramétrico (Teste Kruskal-Wallis). Resultados: O grupo Diabético apresentou perdas significativas na amplitude do PERG, na discriminação de cores no eixo protan, área da elipse e nas frequências espaciais avaliadas da função da sensibilidade ao contraste, além de disfunção dos fatores endoteliais comparado ao grupo Controle. O grupo diabético atleta apresentou concentração maior de óxido nítrico comparado ao grupo Diabético sedentário. Não foram encontradas correlações entre os fatores endoteliais e as funções visuais. Conclusão: foram encontradas perdas funcionais na avaliação psicofísica e eletrofisiológica de pacientes com diabetes tipo 1. Os achados deste estudo confirmam a hipótese de que as perdas visuais sejam de origem neural pós - receptoral. Aumento na concentração de óxido nítrico encontrado em pacientes diabéticos atletas, confirmam os achados da literatura de que o exercício físico é capaz de aumentar a biodisponibilidade deste fator endotelial. Entretanto esse aumento de biodisponibilidade não se refletiu em recuperação das perdas nas funções visuais, uma vez que não houve correlação entre as alterações dos fatores endoteliais e os resultados da avaliação visual. A conclusão, em resumo, é de que o exercício físico não promoveu proteção dos danos visuais verificados em pacientes diabéticos
The study compared visual functions of sedentary and athlete patients with type 1 diabetes, and respective controls, using computerized psychophysical and electrophysiological tests. Materials and Methods: 33 Patients with type 1 diabetes, divided into two experimental groups: athlete diabetics (n = 15; age = 33.33 ± 6.78; rate of disease = 16.19 ± 6.63) and sedentary diabetics ( n = 18 age = 28.94 ± 6.04; rate of disease = 15.92 ± 8.46) and 40 control subjects: athlete control (n = 20; age = 32.0 ± 5.61) and sedentary control (n = 20; age = 27.05 5.60) were subjected to tests of: color vision and contrast sensitivity - Cambridge Colour Test - CCT; pattern electroretinogram (PERG) and laboratorial analysis of nitric oxide and endothelin using chemiluminescence and ELISA. The comparisons between groups were made through the nonparametric (Kruskal-Wallis test). Results: compared the control group, the diabetic group showed significant losses (1) in color discrimination in the protan axis and in ellipse area (2) in several spatial frequencies of the luminance spatial contrast sensitivity function; (3) a reduction in PERG amplitude and (4) dysfunction of endothelial factors. The athlete diabetic group showed increased concentration of nitric oxide compared to the sedentary diabetic group. No correlations were found between the endothelial factors and visual functions. Conclusion: losses in psychophysical and electrophysiological functions were found in patients with type 1 diabetes. The findings support the hypothesis that visual losses are due to the post-receptoral pathways. Increased nitric oxide concentration found in athlete diabetic patients, confirm the findings of the literature that physical exercise can increase the bioavailability this endothelial factor. However this increase in bioavailability was not reflected in the recovery of losses in visual functions, since there was no correlation between changes in endothelial factors and results of visual assessment. In conclusion, the exercise did not promote protection against visual losses due to diabetes

O Diabetes Melitus (DM) é uma doença crônica que compromete vários aspectos da saúde. Uma das complicações mais prevalentes associada à DM é a retinopatia diabética (RD), que produz perdas visuais em várias funções, podendo levar à cegueira. Essas perdas são detectáveis mesmo antes do aparecimento de sinais de retinopatia diabética e sua detecção pode servir para melhor monitoramento, prevenção e tratamento da RD. Utilizando testes psicofísicos e eletrofisiológicos computadorizados de última geração, o presente projeto investiga a discriminação de cores, sensibilidade ao contraste e o padrão das respostas eletrofisiológicas do eletrorretinograma multifocal (mfERG) em vinte pacientes (Idade=28,20 DP = 7,12) com Diabetes Mellitus tipo 1 sem sinais clínicos de retinopatia comparando-os com vinte sujeitos controle (Idade = 28,29 anos DP = 5,03) sem diabetes, ou outras doenças. A discriminação de cores foi avaliada pelo CCT (Cambridge Colour Test) para a discriminação de cores, e a sensibilidade ao contraste programa Metropsis (Cambridge Research System, Ltd), utilizando grades senoidais verticais em sete freqüências espaciais (0,2; 0,5; 1; 2; 5; 10 ; 20 cpg) A função eletrofisiológica da retina foi avaliada pelo eletrorretinograma multifocal (mfERG). A comparação dos dados entre grupos foi feita por ANOVA. No CCT, no protocolo Trivector, os limiares de discriminação cromática dos pacientes foram significativamente mais elevados que os do grupo controle em todos os eixos protan (p = 0,026), deutan (p= 0,012) e tritan (p = 0,001) e no protocolo das elipses a área de discriminação foi significativamente maior que a dos controles (p = 0,002), com elipses próximas de círculos indicando perdas de discriminação difusas. A sensibilidade ao contraste também mostrou-se reduzida, com diferença significativa nas frequências espaciais 0,2 (p = 0,037) e 5 (p = 0,004) cpg. No mfERG, o grupo DM apresentou tempo implícito significativamente maior em N1 0º (p = 0,03) e N2 5º (p = 0,04) e amplitude reduzida em N2 20º (p = 0,04) e 25º (p = 0,02). Concluímos que o grupo de pacientes com diabetes tipo 1 estudado, apresenta perdas comportamentais e eletrofisiológicas de função visual, mesmo na ausência de retinopatia, Estes achados confirmam resultados da literatura obtidos com outros testes
Diabetes Mellitus (DM) is a chronic disease that compromises different aspects of human health and at different times during its progression.. One of the most prevalent complications associated with DM is diabetic retinopathy (DR), which produces losses in different visual functions and can result in blindness. The visual losses can be detected prior to the development of DR and can lead to improvements in the control, prevention and treatment of DR. The present work investigates the color discrimination, contrast sensitivity and the electrophysiological responses patterns of the multifocal electroretinogram (mfERG) using the latest generation of psychophysical and electrophysiological tests in twenty patients (age=28.20; SD=7.12) with Diabetes Mellitus type 1 without DR compared to twenty subjects (age=28.29; SD=5.03) without diabetes and ocular disease. The color discrimination was performed through CCT (Cambridge Colour Test) and contrast sensitivity by Metropsis software (Cambridge Research System, Ltd) using vertical sine wave gratings in seven spatial frequencies (0.2; 0.5; 1; 2; 5; 10; 20 cpd). The retinal electrophysiological function was evaluated with mfERG. The data comparison among groups was performed with ANOVA test. In the Trivector protocol of CCT the diabetic patients showed differences in all axes protan (p = 0,026), deutan (p = 0,012) and tritan (p = 0,001); in the elipses protocol there was a diffuse loss in the patients discrimination (p = 0,002). The contrast sensitivity was reduced in the diabetic group, in particular to the spatial frequencies of 0.2 (p = 0,037) and 5 (p = 0,004)cpd. The results of mfERG from the DM group showed an implicit time bigger in N1 0º (p = 0,03) and N2 5º (p = 0,04) (0º) compared to the control group and a reduced amplitude of N2 20º (p = 0,04) e 25º (p = 0,02). In conclusion, the patients with diabetes type 1 present with behavioral and electrophysiological visual losses, however, they do not show retinopathy. These findings confirm previous results shown in the literature from other tests

Mesmo antes do estabelecimento de retinopatia detectável no exame clínico, a visão de cores e a sensibilidade ao contraste podem estar afetadas (Dean e cols., 1997; Kurtenbach e cols., 1999). Os déficits sensoriais têm sido atribuídos a alterações vasculares e da função de fotorreceptores (Greenstein e cols., 2000; Lieth e cols., 2000). Contudo, poucas conclusões acerca dos mecanismos fisiopatológicos têm sido obtidas. Este trabalho teve por objetivo identificar - em pacientes diabéticos tipo 2 com fundo de olho normal - possíveis alterações na visão de cores e sensibilidade ao contraste cromático e acromático e correlacionar os prejuízos sensoriais com a função eletrofisiológica da retina. A avaliação sensorial foi feita utilizando o Teste de Cores de Cambridge e o teste de sensibilidade ao contraste Psycho (Ventura e cols., 2003a, Ventura e cols., no prelo) e a função eletrofisiológica foi avaliada usando o eletrorretinograma de campo total (ERG). Os resultados dos pacientes diabéticos (n= 40; idade= 56 anos ± 9 e tempo de diabetes= 7 anos ± 9) foram comparados aos de grupos equiparado por idade. O limiar de discriminação de cores no eixo protan foi superior ao limite normal em 50% dos pacientes, no eixo deutan em 37% e tritan em 28%. A sensibilidade ao contraste cromático nos eixo vermelho/verde e azul/amarelo dos pacientes entre as freqüências espaciais de 0,2 a 2 cpg foi em média 10 dB menor que a dos pacientes, enquanto que na função de sensibilidade ao contraste acromático entre as freqüências espaciais de 0,3 a 20 cpg, a sensibilidade dos pacientes foi apenas 6 dB menor que a dos controles. No ERG, os componentes mais alterados foram os relacionados à atividade da retina interna. A amplitude da onda-b na resposta de bastonetes e dos potenciais oscilatórios foi inferior aos limites normais para 24% e 39% dos pacientes, respectivamente, e as latências correspondentes foram mais lentas em 45% e 76% dos pacientes. A perda da discriminação de cores dos pacientes teve padrão difuso; contrariando relatos anteriores de que a diabete provoca defeito da visão de cores no eixo tritan. Os resultados de sensibilidade ao contraste mostraram que o processamento cromático foi claramente mais afetado que os sistemas relacionados ao processamento acromático. Os dados do ERG indicaram haver alteração da atividade da retina interna. Estes achados confirmam e ampliam dados anteriores e sua aplicação clínica pode mudar o conceito de retinopatia diabética.
Before the establishment of retinopathy detectable in the ophthalmologic examination, color vision and contrast sensitivity may be altered in diabetic patients. (Dean e cols., 1997; Kurtenbach e cols., 1999). The sensory deficits have been attributed to vascular alterations and to (Greenstein e cols., 2000; Lieth e cols., 2000). However, there are no definite conclusions about the pathological mechanisms involved in the vision losses. The objective of this work was to identify in patients with type 2 diabetes and normal fundus, possible alterations in color vision and chromatic and achromatic contrast sensitivity, and to correlate the sensory losses with the electrophysiological function of the retina. The psychophysical evaluation was made using the computerized Cambridge Colour Test and PSYCHO contrast sensitivity test. (Ventura e cols., 2003a, Ventura e cols., in press). Electrophysiological function was assessed using the full field electroretinogram (ERG). Patient\'s results (n= 40; age= 56 years ± 9 time of diabetes= 7 years ± 9) with results obtained with age-matched controls. The color discrimination threshold was higher than the normal limit in 50% of the patients in the protan axis, in 37% in the deutan axis and in 28% in the tritan axis. Chromatic contrast sensitivity in both the red/green and the blue yellow axes showed a loss of about 10 dB in patients as compared to controls throughout the frequencies tested (0.2 to 2cpd). In the achromatic contrast sensitivity function the loss found in patients was smaller, of about 6 dB throughout the frequency range tested (3 to 20 cpd). In the ERG b-wave and in the oscillatory potentials the amplitudes were smaller, respectively, in 24% and 39% of the patients compared to controls. The corresponding latencies were longer in 45% and 76% of the patients. The pattern of color discrimination losses of the patients indicates that there is a diffuse loss of color vision, as opposed to most previous results indicating that tritan losses. The contrast sensitivity results showed that the chromatic pathways were more affected than the achromatic pathways. The alterations found in the full field ERG are suggestive of inner retina losses. The present findings confirm and extend previous reports. Their clinical application may change the concept of diabetic retinopathy.

Background: Previous research has shown that cataracts and cataract surgery impact upon driving and vision performance. The research on driving has primarily relied upon self-reported performance measures or simulation techniques to determine the results. Many studies have also shown visual function, including visual acuity, contrast sensitivity and disability glare, to improve following cataract surgery. Limitations of these studies are that (a) patients self-perception may not reflect actual driving performance, (b) simulation studies make inferences about real world driving performance and ( c) studies in clinical settings lack real world applications. Aims: To investigate the effect of cataract surgery on actual driving and vision performance. Subjects: Sixteen subjects (mean age 71.31±8.53 yrs) who underwent bilateral cataract surgery and 16 control subjects (mean age 66.31 ± 7.00 yrs) who had VA 6/7.5 or better and an absence of eye disease participated in the study. All subjects held a current drivers license. Methods: Vision and driving performance were measured before and after cataract surgery in the first and second eye of the cataract subjects. Driving performance was measured under day-time conditions on a closed road circuit as described by Wood and Troutbeck, (1994), measures included, road sign recognition, course time, road obstacle detection, reaction time, reversing, lane-keeping, gap perceptions and manoeuvring. Self-reported driving performance was measured using the Activities of Daily Vision Scale (ADVS) described by Mangione et al. (1992). Vision measures included, visual acuity, contrast and glare sensitivity. The control group completed the same series of trials with similar times between testing sessions. Results: Significant improvements (p < 0.05) in driving performance measures were shown after bilateral cataract surgery, including the number of road signs seen, driving course time and the number of low contrast road obstacles seen and avoided. Visual performance improved significantly after bilateral cataract surgery for binocular visual acuity and contrast sensitivity with and without disability glare measured by the Brightness Acuity Tester. Patient's self-perceptions of vision and quality of life as measured by the ADVS also displayed similar improvements. Conclusions: Bilateral cataract surgery significantly improved driving and vision performance. This was also reflected by patient's self-perceptions of their performance.

This study is a thesis for the Master of Science degree in Media Technology and Engineering at the Department of Science and Technology, Linkoping University. It was accomplished from November 2002 to May 2003.

Objective image quality measures play an important role in various image processing applications. In this paper quality measures applied on halftoned images are aimed to be in focus. Digital halftoning is the process of generating a pattern of binary pixels that create the illusion of a continuous- tone image. Algorithms built on this technique produce results of very different quality and characteristics. To evaluate and improve their performance, it is important to have robust and reliable image quality measures. This literature survey is to give a general description in digital halftoning and halftone image quality methods.

Transcranial random noise stimulation (tRNS) is a recent neuro-modulation technique whose effects at both behavioural and neural level are still debated. In the first experiment the well-known phenomenon of motion aftereffect (MAE) was exploited in order to investigate the effects of high- versus low-frequency tRNS on motion adaptation and recovery. 36 Participants were asked to evaluate the MAE duration following the exposure of a circular rotating and expanding grating for 30 seconds, while being stimulated with either Sham or tRNS across different blocks. Different groups were administered with either high- or low-frequency tRNS. Stimulation sites were bilateral V5/MT, early visual areas or frontal areas. Results demonstrated that, whereas no effects on MAE duration were produced by stimulation of early visual areas or frontal areas, high-frequency tRNS over area V5/MT caused a significant decrease in MAE duration whereas low-frequency tRNS (over the same area) caused a significant corresponding increase in MAE duration. These data indicate that high- versus low-frequency tRNS has opposite effects on the unbalance, created by adaptation, between neurons tuned to opposite motion directions, and thus on neuronal excitability. Following repeated practice on a visual task, perceptual learning (PL) produces a long lasting improvement of visual functions such as an increase of visual acuity (VA) and contrast sensitivity (CS) both in participants with amblyopia and refractive defects. This improvement has been observed with contrast detection tasks in the presence of lateral masking (contrast detection of a central Gabor stimulus flanked by two high contrast Gabors), known to bring about an increase of lateral interactions between detectors in early cortical pathways. Improvement has also been revealed in the absence of flankers in healthy individuals and those with amblyopia. In the second experiment, a single Gabor PL regime (in the absence of lateral masking) was investigated in a group of participants with mild myopia. This study seeks to understand whether a perceptual training regime really needs to be based on lateral interactions in cases where poor vision is not due to cortical dysfunctions, such as in myopia. 10 participants with mild myopia (max -2D) were recruited. The participants carried out an 8-week behavioural training using a single Gabor PL paradigm, completing a total of 24 sessions. Results indicate that training using a single Gabor protocol results in a VA improvement of 0.16 logMAR. The present study supports the idea that, in the absence of cortical deficits, such as in myopia, some sort of compensatory mechanism can take place at the cortical level by means of PL, resulting in more effective processing of the received blurred input. However, with respect to training based on lateral masking, here we found that improvement of visual functions was smaller and limited to VA. This might suggest that trainings based on lateral masking, able to modify the strength of facilitatory and inhibitory lateral interactions, could be more effective for an optimal recovery of blurred vision. It has recently been suggested how PL can be boosted by concurrent high-frequency tRNS (hf-tRNS). It has also been shown how PL can generalize and produce an improvement of visual functions in participants with mild refractive defects. By using three different groups of participants, with 10 participants in each group (single-blind study), the third experiment tested the efficacy of a short (8 sessions) single Gabor contrast-detection training with concurrent hf-tRNS in comparison with the same training combined with Sham stimulation or hf-tRNS with no concurrent training, in improving VA and CS of individuals with uncorrected mild myopia. Results show that a short training with a contrast detection task is able to improve VA and CS only if coupled with hf-tRNS, whereas no effect on VA and marginal effects on CS are seen with the sole administration of hf-tRNS. The results support the idea that, by boosting the rate of PL via the modulation of neuronal plasticity, hf-tRNS can be successfully used to reduce the duration of perceptual trainings while, at the same time, increasing their efficacy in producing PL and generalization to improved VA and CS in individuals with uncorrected mild myopia. A final experiment extended the aforementioned results onto patients with a cortical visual deficit. Amblyopia is a visual disorder due to an abnormal pattern of functional connectivity of the visual cortex and characterized by several visual deficits of spatial vision including impairments of VA and of the contrast sensitivity function (CSF). Despite being a developmental disorder caused by reduced visual stimulation during early life (critical period), several studies have shown that extensive visual perceptual training can improve VA and CS in people with amblyopia even in adulthood. In this study, a much shorter perceptual training regime was assessed with respect to the standard PL trainings, in association with hf-tRNS in comparison to the perceptual training combined with Sham stimulation, whether it was able to improve visual functions in a group of adult participants with amblyopia. Results demonstrated that, in comparison with previous studies where a large number sessions with a similar training regime were used, here just eight sessions of training in contrast detection under lateral masking conditions combined with hf-tRNS, were able to substantially improve VA and CS in adults with amblyopia. In conclusion, this thesis investigates the use and efficacy of tRNS with and without PL on visual cortical excitability and plasticity, in the context of visual functioning.
La stimolazione transcranica a rumore casuale (transcranial random noise stimulation - tRNS) è una tecnica neuromodulatoria recente i cui effetti a livello comportamentale e neurale sono ancora dibattuti. Con il primo esperimento è stato utilizzato l’effetto postumo di movimento, denominato altresì motion aftereffect (MAE), per indagare gli effetti della tRNS ad alta e a bassa frequenza sull’adattamento al movimento e sul suo recupero. A trentasei partecipanti è stato chiesto di valutare la durata del MAE evocato dalla visione di un reticolo con movimento di rotazione ed espansione per 20 secondi, contemporaneamente alla tRNS o ad una stimolazione fittizia (Sham), somministrate in diversi blocchi. A gruppi di partecipanti diversi è stata somministrata la tRNS ad alta o a bassa frequenza. I siti di stimolazione potevano essere l’area V5/MT bilateralmente, le cortecce visive precoci o le aree frontali. I risultati hanno mostrato che, mentre non è stata trovata nessuna variazione con la stimolazione delle aree visive precoci o delle aree frontali, la tRNS ad alta frequenza sull’area V5/MT ha determinato una riduzione significativa della durata del MAE mentre la tRNS a bassa frequenza (sulla stessa area V5/MT) ha provocato un corrispondente incremento della durata del MAE. Questi dati indicano che la tRNS ad alta e a bassa frequenza hanno effetti opposti sullo squilibrio, creato dall’adattamento, tra neuroni che rispondono a direzioni di movimento opposte, e quindi effetti opposti sull’eccitabilità neuronale. Questi dati indicano che la tRNS ad alta e a bassa frequenza ha effetti opposti sullo squilibrio, creato dall’adattamento, tra neuroni che rispondono a direzioni di movimento opposte, e quindi effetti opposti sull’eccitabilità neuronale. Attraverso un training ripetuto con un determinato compito visivo, l’apprendimento percettivo (perceptual learning – PL) produce un miglioramento duraturo di funzioni visive quali un incremento dell’acuità visiva (AV) e della sensibilità al contrasto (SC) in partecipanti con ambliopia o con difetti refrattivi. Tale miglioramento è stato osservato attraverso l’utilizzo di un training di detezione di contrasto in presenza di flankers (mascheramento laterale), che permette di ottenere un potenziamento delle interazioni laterali tra detettori ai primi livelli di elaborazione visiva corticale. Un simile miglioramento è stato osservato anche in assenza di flankers, sia in partecipanti sani che in partecipanti con ambliopia. Nel secondo studio è stato investigato l’effetto di un training con Gabor singoli (in assenza quindi di mascheramento laterale) in un gruppo di partecipanti con miopia lieve. Con questo studio si è cercato di capire se, per ottenere un miglioramento delle funzioni visive, un training percettivo debba essere necessariamente basato sulle interazioni laterali nel caso in cui una visione sfocata sia dovuta a una disfunzione non corticale come la miopia. 10 partecipanti con miopia lieve (sino a -2D) hanno partecipato ad un training comportamentale di 8 settimane (per un totale di 24 sessioni) utilizzando un compito di detezione di contrasto di Gabor singoli. I risultati mostrano un miglioramento in AV, in assenza di correzione ottica, di 0.16 LogMAR, suggerendo che, pur in assenza di deficit corticali, un meccanismo di compensazione possa aver luogo a livello corticale attraverso il PL, ottenendo perciò un’elaborazione più efficace dall’immagine sfocata in ingresso. Tuttavia, rispetto al training basato sul mascheramento laterale, in questo studio abbiamo trovato un miglioramento delle funzioni visive più contenuto e limitato alla AV. Questo può suggerire come il training basato sul mascheramento laterale, capace di modificare la forza delle interazioni laterali facilitatorie e inibitorie, possa essere più efficace per un recupero ottimale della visione sfocata. E’ stato suggerito di recente come il PL possa essere potenziato dalla contemporanea somministrazione di tRNS ad alta frequenza. D’altro canto, è stato anche mostrato come il PL possa generalizzare e causare un miglioramento delle funzioni visive in partecipanti con difetti refrattivi lievi. Utilizzando tre diversi gruppi di partecipanti con 10 partecipanti per gruppo (disegno sperimentale in cieco), con il terzo esperimento si è voluto testare l’efficacia di un breve (8 sessioni) training di detezione di contrasto con Gabor singoli, con contemporanea somministrazione di tRNS ad alta frequenza, confrontata con lo stesso training con contemporanea somministrazione di stimolazione fittizia (Sham), e con tRNS ad alta frequenza in assenza di training comportamentale, nel miglioramento di AV e SC di partecipanti con miopia lieve non corretta. I risultati mostrano che un breve training di detezione di contrasto è in grado di migliorare AV e SC solo se unito a contemporanea tRNS ad alta frequenza, mentre nessun sostanziale miglioramento è stato osservato con la sola somministrazione della tRNS. Questi risultati supportano l’idea che, potenziando la velocità del PL attraverso la modulazione della plasticità neurale, la tRNS ad alta frequenza può essere utilizzata con successo per ridurre la durata dei training percettivi, aumentando allo stesso tempo l’efficacia nel produrre PL e generalizzazione (miglioramento di AV e SC) in individui con miopia lieve non corretta. Un ultimo esperimento ha permesso di estendere i summenzionati risultati su pazienti con deficit visivo di natura corticale. L’ambliopia è un disturbo visivo dovuto ad un pattern di connettività funzionale abnormale della corteccia visiva, caratterizzato da diversi deficit in visione spaziale tra cui in AV e in SC. Pur essendo un disturbo dello sviluppo causato da stimolazione visiva ridotta o alterata durante l’infanzia (periodo critico), diversi studi hanno mostrato come training percettivi visivi possano migliorare AV e SC in individui con ambliopia anche in età adulta. In questo studio, è stata valutata l’efficacia di un training percettivo molto più breve rispetto alle durate standard (associato alla tRNS ad alta frequenza rispetto allo stesso training unito a stimolazione Sham), nel miglioramento delle funzioni visive di un gruppo di partecipanti adulti con ambliopia. I risultati hanno mostrato che 8 sessioni di training di detezione di contrasto con mascheramento laterale, unito a tRNS ad alta frequenza, permettono un sostanziale miglioramento di AV e SC in partecipanti adulti con amblyopia. In conclusione, in questo elaborato si è voluto testare l’efficacia della tRNS con e senza PL sull’eccitabilità e la plasticità della corteccia visiva, nel contesto dei meccanismi delle funzioni visive.

A number of studies have investigated various visual functions of visually impaired subjects and how their visual functions relate to the subjects' ability to travel in their environment. Most studies have shown that visual field and contrast sensitivity are the most important visual factors in determining how well visually impaired subjects travel in their environment. From the outcome of the studies, some aspects of vision are known to play important roles in mobility performance of visually impaired subjects. However, in all these studies, researchers have used visually impaired subjects with differing degrees of mobility skills. The mobility performance measured in previous studies may differ among subjects depending on the level of their mobility skills rather than differences in visual function. One of the main factors which may affect subjects' mobility skills is whether or not they have had orientation and mobility (O&M) training. Anecdotal evidence reported by mobility instructors and visually impaired clients suggests that O&M instruction does improve independent travel skills. In view of the limitations of previous studies, the current study attempted to determine the effect of O&M training on vision and mobility performance of visually impaired adults. Vision and mobility performance of a group of visually impaired subjects were examined before and after O&M training. As the same group of subjects were investigated, the effects of other factors which influenced their mobility skills may be controlled. Based on the best predictors of mobility performance, vision criteria for O&M training referral were recommended. Methods. Vision and mobility performance of 2 groups of visually impaired subjects with various ocular diseases were assessed: the experimental group T who were referred and received mobility training and the control group NT with no previous mobility training and were not referred for training. Visual performances were measured binocularly as high and low contrast visual acuities, letter and edge contrast sensitivities and kinetic visual fields. The subjects' mobility performance was measured on an indoor mobility course: 1) walking efficiency was assessed as percentage preferred walking speed (PPWS) 2) mobility incidents were assessed as errors made during travel on the course. Vision and mobility performances were measured before training and approximately 4 weeks after completion of training for group T whilst group NT was assessed at two visits with a similar time period between visits as for group T. A questionnaire was administered to each group at both visits and six months after the second visit. Results. Walking efficiency of group T improved with short-term practice immediately following O&M training but there was no improvement due to long-term practice or training. On the other hand, there was no improvement in error score either due to practice or training immediately after O&M training. Error score of all subjects improved as a result of prior experience. Self-reported mobility performance did not improve immediately after O&M training but improved six months after training. Stepwise multiple regression analysis showed that visual field was a significant predictor before and after O&M training; it accounted for 20.4 percent and 31.2 percent of the variance in PPWS and error score respectively before training whilst accounting for 20.0 percent and 16.8 percent of the variance in PPWS and error score respectively after training. Stepwise multiple regression analysis of groups T and NT together showed that LCV A and inferior remaining visual field were best predictors of PPWS and error score respectively; PPWS began to deteriorate when LCVA was 6/150 or worse whilst error score began to decline when inferior remaining visual field was 45 degrees radius or less (between the field extent of 225 and 315 degrees). Conclusions. Mobility performance of visually impaired adults may be improved following O&M training, however, further research needs to be conducted to ascertain the level of improvement in performance over time. Visual field was shown to play a significant role in mobility performance of visually impaired adults regardless whether or not they have had O&M training, however, further research is required to ascertain the role of LCV A in walking efficiency. Tentative criteria for O&M training referral were recommended: LCVA 61150 or worse and/or inferior remaining binocular visual field of 45 degrees or less using the target IV 4 E. However, further research is needed to ascertain if these criteria are applicable to other visually impaired groups.

Differences in orientation and mobility of people with different types of visual impairment have received little attention in the literature. Typically, studies have assessed the mobility performance of either a heterogenous group of subjects with low vision (ie. mixed ocular diseases) or a homogenous group of subjects with a particular eye disease (E§ Retinitis Pigmentosa: RP). There have been few investigations of both mobility performance and vision determinants of mobility in subjects with central visual field (VF) loss. Similarly, mobility performance and its relationship with vision of subjects with contrasting types of VF loss have not been systematically investigated. The work described in this thesis aims to provide a better understanding in these areas. The first study compared the vision and mobility performance of subjects with central VF loss, modelled through Age-related Macular Degeneration (ARMD), and subjects of similar age with normal vision. Elderly subjects with ARMD, when considered as a homogenous group, had no more difficulty with mobility than the normal vision subjects. This was true for both the efficiency (speed) and safety (errors) aspects of mobility performance. The height and luminance of objects did not affect the number of errors made by central VF loss subjects. The sub-group of central VF loss subjects with an absolute binocular scotoma had significantly more difficulty with mobility than the normally sighted subjects. The significance of a binocular scotoma was further demonstrated through the results of the vision determinants of mobility performance. VF measures, relating directly or indirectly to the presence or size of a binocular scotoma, emerged as the best predictors of mobility performance. The second study compared the vision and mobility performance of subjects with peripheral VF loss, modelled through RP, and subjects of similar age with normal vision. Peripheral VF loss subjects had significantly impaired mobility compared to normal vision subjects. This was evident in both the efficiency (speed) and safety (errors) aspects of mobility performance. In particular, the peripheral VF loss subjects found low luminance and inferiorly- and superiorly-placed objects hazardous while navigating through the mobility course. Residual VF measures related to the central 10° radius VF zone emerged as significant predictors of mobility performance. The third study compared the vision and mobility performance of subjects with central and peripheral VF loss. The results of this study showed that, unlike central VF loss, peripheral VF loss was associated with decreased mobility performance. Peripheral VF loss subjects, despite being younger, walked significantly slower and made mo~e errors than the central VF loss subjects. Other differences in mobility performance between the contrasting VF loss groups included the impact of object luminance and position. Similarities in performance included the benefits of familiarity with the course and the degradation of performance under conditions of glare and reduced illumination. Again the importance of the central 10° radius VF for mobility was shown, these VF measures being the best predictors of mobility performance for both VF loss groups. Another aim of this work was to develop and assess the effectiveness of VF scoring based on cortical magnification. Despite the fact that these methods of VF scoring emphasise the central VF, which was shown to be a significant predictor of mobility performance, these methods did not emerge as better determinants of mobility performance than conventional VF scoring methods. This may be a consequence of the available equations and measurement errors associated with kinetic VF measurement. The work described in this thesis provides an improved understanding of the mobility performance and its relationship with vision in low vision subjects with contrasting types of VF loss. The results of these experiments lead to recommendations relating to the vision assessment and referral criteria of low vision patients. Since many determinants of mobility performance related to the central 10° radius VF zone, future work should aim to improve VF measurement and scoring methods including scoring techniques based on cortical magnification, where central VF areas are given prominence. Other future studies should evaluate the vision and mobility performance of low vision subjects with a greater number of forms of VF loss to extend on the work reported in this thesis.

Concern about falling (CF) is a significant health issue among older people, leading to activity restriction, physical decline, and increased falls risk. Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss among older people, yet little is known about CF in this population. High levels of CF were demonstrated among those with AMD, predicted by reduced visual function, and other physical and psychological factors. Over a 12-month period, CF increased, more so than in general older populations. These results provide an important basis for developing interventions to manage excessive CF, promote activity participation and reduce falls risk.

PURPOSE: This thesis presents the results of a prospective, double-blind and randomized clinical trial conducted at the Hospital de Sant Pau i la Santa Creu ofBarcelona.lts main objective was to assess and compare visual qualityofpatients implanted with different designs of multifocal intraocular lenses (MIOLs), as well as a monofocallens as control group. METHOD : The MIOLs used in the studywere the refractive ReZoom NXG, with add power of +3.00D, the aspheric hybrid (apodized diffractive-refractive) AcrySof ReSTOR SN6AD1, with add power of +3.00D, the spherical hybrid (apodized diffractive-refractive) AcrySof ReSTOR SN60D3, with add power of +4.00D and the aspheric diffractive Tecnis ZMAOO, with add power of +4.00D. The monofocallens was the aspheric Tecnis ZA9003. All clinical measurements were conducted under best post-operative optical correction. One and three months after the intervention visual acuity (VA) was as ses sed at far (VF), intermediate (60 cm) (VI) and near (33 and 40 cm), (VN) distances. The SIFFI-MAVtest, which is the standard test in this type of clinical trials , was used for VF and the test ofthe Departament de Treball de la Generalitat de Catalunya for VN. At three months patients were administered two questionnaires to investigate subjective qualityofvision and qualityoflife and at six months contras!sens itivity (CS) and stereoacuity were assessed. Contras!sensitivity was explored at distance under photopic, mesopic and mesopic with glare conditions with the CSV-1000 and at near in photopic conditions with the VCTS 6000 test. Two tests were employed to meas ure stereoacuity: the polarized Titmus test and the anaglyphic TNO. RESULTS: No statistically significan!differences (p>0.05) were found in VF amongst the MIOL under study. For VI, the ReZoom , SN6AD1 and Tecnis offered the bes!performance, without differences amongst them . M. 33 cm, the best VN was obtained with the aspheric MIOLs, withoutdifferences amongstthem , and at40 cm, the bestVN was obtained with the monofocallens . Regarding CS at far, no differences were found amongst the MIOLs under any of the illum ination conditions. Alnear, the aspheric lenses offered the best results in terms of CS. However, the best CS at any distance and illumination was obtained with the monofocallens . No difference was found amongst the MIOLs in stereoacuity as meas ured with the Titmus test, although with the TNO test the refractive ReZoom offered the best outcome. In terms of subjective visual quality, patients im planted with MIOLs reported good vis ion with and without best optical correction at all distances , al so presenting with spectacle independence at all distances . Photic phenom ena were found to occur in patients im planted with MIOLs , albeit less in apodized designs . Patient satisfaction with MIOL designs was high and they did not report any problems when conducting daily activities . With the monofocallens there was less spectacle independence, less occurrence of photic phenomena and good visual satisfaction. CONCLUSION: the present findings may assist practitioners when selecting the best intraocular lens design for each patient, particularlythose with high visual demands at VP and VI.
En esta tesis se presentan los resultados de un ensayo clínico prospectivo, randomizado y doble ciego realizado en el Hospital de Sant Pau i la Santa Creu de Barcelona. Su objetivo principal fue evaluar la calidad visual de pacientes implantados con diferentes diseños de lentes intraoculares multifocales (MIOL), comparándolos entre sí y con una lente intraocular monofocal como control. MÉTODO: Las lentes multifocales utilizadas fueron la refractiva ReZoom NXG con adición de +3.00D, la asférica híbrida (difractiva apodizada-refractiva) AcrySof ReSTOR SN6AD1 con adición de +3.00D, la esférica híbrida (difractiva apodizada-refractiva) AcrySof ReSTOR SN60D3 con adición de +4.00D y la asférica difractiva Tecnis ZMAOO con adición de +4.00D. Como lente control monofocal asférica Tecnis Monofocal ZA9003. Todas las medidas clínicas fueron realizadas con la mejor corrección óptica postoperatoria. Tanto al mes como a los tres meses de la intervención se analizó la agudeza visual (AV), en visión lejana (VL), intermedia (60 cm) (VI) y próxima (33 y40 cm) (VP). Para ello se utilizó el sistema estandarizado para estudio clínicos SIFFI-MAV para VL y el test del Departament de Treball de la Generalitat de Catalunya para VP. A los tres meses se pasó a todos los pacientes dos cuestionarios para evaluar la calidad visual subjetiva y la calidad de vida ya los seis meses se estudió la sensibilidad al contraste (SC) y la estereoagudeza. Respecto a la SC se evaluó en visión lejana bajos tres condiciones de iluminación, fotópica, mesópica y mesópica con deslumbramiento con el test CSV-1000, y en visión próxima en condiciones fotópicas con el test VCTS 6000. En lo que concierne a la visión estereoscópica, se analizó con dos tipos de test, uno polarizado, el Titmus, y otro anaglífico, el TNO. RESULTADOS: El análisis de los resultados determinó que no existían diferencias estadísticamente significativas (p>0.05) en la AV de VL entre las diferentes lentes del estudio. Para Vilas MIOL que proporcionan mejor AV son la ReZoom, SN6AD1 y Tecnis, sin existir diferencias entre ellas. Para la distancia de 33 cm las MIOL asféricas son las que proporcionan mejor sin existir diferencias estadísticamente significativas entre ellas, y para 40 cm con la lente SN6AD1 se obtiene mejor AV. Sin embargo, tanto a 33 cm como a 40 cm la lente que proporciona mejor AV es la monofocal, anteponiendo la correspondiente adición. Los resultados de la SC en visión lejana no mostraron diferencias estadísticamente significativas entre las MIOL bajo ningún tipo de iluminación. Para VP las MIOL que obtuvieron mejor sensibilidad al contraste fueron las dos lentes asféricas. Sin embargo, la lente monofocal fue la que mostró mejor SC tanto en VL como en VP. En lo que concierne a la AV estereoscópica no se hallaron diferencias entre las MIOL con el test Titmus, pero sí con el TNO, a favor de la MIOL refractiva ReZoom. Desde el punto de vista de la calidad visual subjetiva, los pacientes implantados con MIOL manifiestan que su visión tanto con la mejor corrección óptica como sin ella era buena a todas las distancias y presentaban independencia de gafas también a todas las distancias. Los fenómenos disfóticos se hallan principalmente en las MIOL, aunque menos con las lentes apodizadas. La satisfacción de los pacientes con las MIOL es alta y no manifestaban dificultades para realizar las actividades de la vida cotidiana. Con la lente monofocal hay menor independencia de gafas, escasa frecuencia de fenómenos disfóticos y alta satisfacción visual con el implante. CONCLUSIÓN: los presentes resultados pueden contribuir a la decisión del tipo de lente intraocular más adecuado para cada paciente, especialmente aquellos con altas demandas visuales en VP y VI

O albinismo e uma alteracao genetica rara que compromete a producao de melanina. As alteracoes clinicas consistem na falta de pigmentacao da pele, cabelo e pelos. Apresenta alteracoes oftalmologicas importantes, que comprometem a acuidade visual de forma severa, na grande maioria dos casos. As alteracoes oftalmologicas sao, ametropias, nistagmo, rarefacao do epitelio pigmentado da iris e da retina, hipoplasia foveal e decussacao anomala do nervo optico. Este estudo foi dividido em tres diferentes partes com os seguintes objetivos principais: Parte 1: Analise comparativa entre o grau de transparencia da iris (GTI), o grau de transparencia da retina (GTR) e a espessura da regiao macular com a acuidade visual nos pacientes com albinismo. Parte 2: Teste de sensibilidade ao contraste espacial de luminancia e ofuscamento com lentes de contato filtrantes em ambientes claros e escuros. Parte 3: Avaliacao da visao de cores, utilizando\\se o teste de Pranchas de Ishihara e o Cambridge Color Test (CCT). Material\' e\' Métodos: Participaram do estudo 121 individuos albinos, com idade media de 31,18 (} 15,47) anos, o que totalizou 242 olhos. Os participantes foram divididos em diferentes grupos nas tres partes do estudo, alguns participaram de uma ou mais partes. Na primeira parte os participantes foram submetidos a consulta oftalmologica, classificacao do grau de transparencia da iris e da retina em uma nova classificacao baseada em quatro diferentes graus de transparencia, alem de avaliacao foveal pelo exame de Tomografia de Coerencia Optica (OCT). Na segunda parte, os participantes foram submetidos ao teste de contraste computadorizado, utilizando lentes de contato filtrante e transparentes, em ambientes claros e escuros. Nesta etapa foi avaliada a influencia da lente filtrante na sensibilidade de contraste visual dos individuos com albinismo. Na terceira parte, os participantes foram submetidos aos testes de Pranchas de Ishihara e de Cambridge Colour Test (CCT), para avaliacao da visao de cores nos pacientes albinos. Resultados: Os resultados foram os seguintes: Parte\'1: A correlacao entre AV logMAR e GTI foi positiva (+0,569) e significativa (p<0,001). A correlacao entre AV logMAR e GTR foi positiva (+0,531) e significativa (p<0,001). A correlacao entre AV logMAR e a espessura macular nao foi significativa (p=0,105). A correlacao entre GTI e GTR foi positiva (+ 0,627) e significativa (p<0,001). A correlacao entre espessura macular e GTI nao foi significativa (p=0,397). A correlacao entre espessura macular e GTR nao foi significativa (p=0,458). Parte 2: Houve melhora estatisticamente significante da sensibilidade ao contraste com as lentes filtrantes em relacao as lentes transparentes no ambiente de ofuscamento (claro), na frequencia de 0,3 cpg, 0,6 cpg e 1,0 cpg (ciclos por grau). Nao houve melhora significante nas frequencia 2,0 cpg e 4,0 cpg. Nao houve melhora estatisticamente significante da sensibilidade ao contraste de lentes filtrantes em relacao as lentes transparentes no ambiente escuro (penumbra) em nenhuma das frequencias espaciais estudadas. Parte\' 3: Todos os individuos com albinismo nao apresentaram nenhuma alteracao de visao de cores no teste de Pranchas de Ishihara. O CCT demonstrou piora no limiar de deteccao de cores significativa nos eixos protan (p=0,021) e deutan (p=0,017), mas nao houve diferenca no eixo tritan (p=0,212). Os testes estatisticos sugerem que uma amostra maior seja estudada para validacao dos resultados
Albinism is a rare genetic alteration that compromises the production of melanine in all body tissues. The clinical alterations are the lack of pigment in the skin and hair. It presents important ophthalmological changes that compromise the visual acuity, in most cases. The ophthalmological changes are: ametropia, nystagmus, iris pigmented epithelium rarefaction, retina pigmented epithelium rarefaction, foveal hipoplasia and abnormal optic nerve decussation. This study has been divided in three different parts and had the following main objectives: Part 1, comparative analysis of the iris transparency degree (ITD), the retina transparency degree (RTD) and macular thickness with the visual acuity in albino patients. Part 2: Spatial contrast sensitivity test of luminance and outshine wearing contact lenses with filters in light and dark environments. Part 3: color vision evaluation using the Ishihara Test and the Cambridge Color Test (CCT). For the study 121 individuals with albinism were included with an average of 31,18 years old } 15,47, a total of 242 eyes. The participants were divided in different groups in the three parts of the study, some participated in one or more parts. In the first part the participants have been through an ophthalmological exam, classification of the iris transparency degree (ITD) and the retinal transparency degree (RTD) by a new classification based in 4 different degrees of transparency. Foveal evaluation by the Optic Coherence Tomography exam (OCT) was made in the first part of this study. In the second part, the participants have been submitted to the computerized contrast test, using filtered and transparent contact lenses in light and dark environments. In this part the influence of the filtering lenses in the visual contrast sensitivity in the albinism patients has been evaluated. In the third part, the participants have been submitted to Ishihara Test and Cambridge Color Test in order to evaluate the color vision in albino patients. The results are as follows: Part\' 1: the correlation between visual acuity in Logarithm of the Minimum Angle of Resolution (logMAR) and ITD was positive (+0,569) and significant (p<0,001). The correlation between visual acuity in logMAR and RTD was positive (+0,531) and significant (p<0,001). The correlation between visual acuity in logMAR and the macular thickness was not significant (p=0,105). The correlation between ITD and RTD was positive (+ 0,627) and significant (p<0,001). The correlation between the macular thickness and the ITD was not significant (p=0,397). The correlation between the macular thickness and the RTD was not significant (p=0,458). Part\'2: There has been a statistically significant improvement of the contrast sensitivity wearing the filtering lenses in relation to the transparent ones in bright environment, in the frequencies of 0,3 cycles per degree (cpd), 0,6 cpd and 1,0 cpd. There has been no significant improvement in the frequencies 2,0 cpd and 4,0 cpd. There has been no statistically significant improvement in contrast sensitivity wearing the filtering lenses in relation to the transparent one in the dark environment (shadow) in any of the spatial frequencies studied. Part\' 3: all albinism patients did not present any color vision change in the Ishihara Test. The CCT has shown a worsening in the color detection threshold in the protan axis (p=0,021) and deutan axis (p=0,017), but there has been no difference in the tritan axis (p=0,212). The statistic tests show that a bigger sample is recommended to confirm part 3 results

Dentre as células ganglionares da retina existe uma pequena população de células que contem melanopsina e respondem diretamente à luz. Estas são as células ganglionares intrinsecamente fotossensíveis (ipRGCs), cujas funções são principalmente não visuais. Dentre as funções não visuais das ipRGCs sua influência na resposta pupilar dependente da luz foi o objeto central desta tese. Tanto a retina interna, através das ipRGCs, quanto a retina externa, através dos bastonetes e cones, fornecem uma informação neural que regula a resposta pupilar à luz (RPL). Este estudo avaliou a integridade das ipRGCs através do RPL em pacientes com glaucoma primário de ângulo aberto (GPAA), leve, moderado e avançado, e em pacientes com síndrome da apnéia obstrutiva do sono (SAOS), moderada e grave. Também foi avaliada a discriminação cromática e a sensibilidade ao contraste espacial de luminância (SC), a perimetria visual e a espessura da retina avaliada por tomografia de coerência óptica (OCT). Foram avaliados 98 participantes: 45 pacientes com GPAA ( 27, 18; idade média = 65,84 + 10,20), 28 pacientes com SAOS ( 14, 14; idade média = 52,93 + 7,13), e 25 controles ( 17, 8; idade média = 54,27 + 8,88). Após o exame oftalmológico foram avaliadas a SC de grades e a discriminação de cores através do Cambridge Colour Test (CCT). A avaliação do RPL foi feita apresentando-se flashes de 470 e 640 nm, de 1s de duração, em 7 luminâncias desde -3 até 2.4 log cd/m2 em um Ganzfeld Q450 SC (Roland Consult). O RPL foi registrado pelo sistema de eye tracker View Point System (Arrington Research Inc.). Os testes foram realizados em ambos os olhos, de forma monocular e no escuro. Para a comparação dos dados entre os grupos, utilizou-se um modelo de equações de estimação generalizada (GEE), para correção da dependência entre os dois olhos. O RPL dos pacientes com GPAA moderado e avançado apresentou redução significativa na amplitude do pico, dependente da severidade do glaucoma, nas diferentes luminâncias tanto para 470 nm quanto para 640 nm, evidenciando redução das contribuições dos cones e bastonetes ao RPL. As contribuições das ipRGCs ao RPL (avaliadas pela amplitude da resposta sustentada entre 6-8 s) foram também significativamente menores em GPAA moderado e avançado. No estado inicial do GPAA as contribuições das ipRGCs para o RPL encontram-se preservadas. No entanto, o GPAA parece afetar o processamento espacial desde o inicio da doença. Nos pacientes com GPAA leve foi observada uma perda acentuada nas faixas baixas de frequência espacial, compatível com prejuízo seletivo das células ganglionares do tipo M. A SC de pacientes com GPAA moderado e avançado mostrou perdas nas faixas baixas e altas de frequência espacial, apontando um prejuízo nas vias parvo- e margnocelulares. Uma perda significativa da discriminação de cores no eixo azul-amarelo foi observada em todos os estágios do GPAA. O RPL nos pacientes com SAOS está parcialmente preservado, não obstante, as respostas da amplitude do pico para o flash de 470 nm diminuem conforme aumenta a severidade da SAOS. As contribuições dos fotorreceptores da retina externa ao RPL, foram significativamente menores em algumas das luminâncias. Não foram observadas diferenças significativas de SC ou discriminação de cores nos pacientes com SAOS. Em conclusão, no estágio moderado e avançado do glaucoma tanto as contribuições das ipRGCs ao RPL quanto as vias M e P, se encontram mais afetadas do que no inicio do GPAA, quando a via parvocelular e as contribuições das ipRGCs ao RPL parecem estar mais preservadas
Among the retina ganglion cells there are a small population of cells containing melanopsin and which respond directly to light. They are the intrinsically photosensitive ganglion cells (ipRGCs), whose functions are mainly non-visual. Among these non-visual functions of the ipRGCs, their influence on the pupillary response as a function of light was the central subject of this thesis. Both the inner retina through the ipRGCs and the outer retina through the rods and cones, provide neural information that regulates the pupillary light response (PLR) to light. This study evaluated the integrity of ipRGCs through PLR in patients with Primary Open Angle Glaucoma (POAG), mild, moderate and advanced, and in patients with Obstructive Sleep Apnea Syndrome (OSAS), moderate and severe. We evaluated also the color discrimination and achromatic spatial contrast sensitivity (CS), visual perimetry and retinal thickness evaluated by Optical Coherence Tomography (OCT). 98 participants were evaluated, 45 patients with POAG ( 27 18; mean age = 65.84 + 10.20), 28 with OSAS ( 14 14; mean age = 52.93 + 7.13) and 25 controls ( 17 8; mean age = 54.27 + 8.88). After the ophthalmological exam it was evaluated the contrast sensitivity and color discrimination measures using the Cambridge Colour Test (CCT). Pupil responses were elicited by Ganzfeld (Q450 SC, Roland Consult) presentation of 1-sec flashes of 470- and 640-nm at 7 luminance from -3 to 2.4 log cd/m2. PLR was measured with the eye tracker system View Point (Arrington Research Inc.). The tests were performed monocularly, on both eyes, in a darkened room. In order to compare data across groups, we used a General Estimating Equations (GEE) to adjust for within subject inter-eye correlations. Patients with moderate and advanced POAG had a significantly decreased PLR that depends on the severity of the glaucoma, for both the 470- and 640-nm stimuli, making evident the reduction of the contributions of the cones and rods to the PLR. The contributions of ipRGCs to PLR (assessed by the amplitude of the sustained response between 6 8 sec) were also significantly lower in patients with moderate and advanced POAG. In the initial and mild stages of POAG the contribution of ipRGCs to the PLR is preserved. However, POAG appears to affect spatial processing from the early stages of the disease. Mild-POAG patients showed a marked loss in the low spatial frequency bands, compatible with selective loss of magnocellular ganglion cells. The CS of patients with moderate and advanced POAG showed losses at both low and high spatial frequencies, suggesting a loss in both parvo- and margnocellular channels. A significant loss of color discrimination along the blue-yellow axis was observed in all stages of POAG. The PLR in patients with OSAS is partially preserved, however the peak amplitude responses for the 470-nm flash decreased with increased severity of OSAS. The contributions of the photoreceptors of the outer retina to the PLR were significantly lower at some of the luminance. Significant differences in CS or color discrimination were not observed in patients with OSAS. In conclusion, in moderate and advanced stages of glaucoma, both the contributions of ipRGCs to PLR as well as the M- and P channels, were found more affected than at the beginning of POAG, in contrast the parvocellular channel and the contributions of ipRGCs on the PLR would be more preserved

Purpose: There is little agreement on the age at which visual acuity (VA) and contrast sensitivity (CS) become adult-like. The ultimate purpose of this thesis was to determine whether VA and CS are adult-like at the age of 6-8 or 9-12 years by using both objective and subjective methods in the same individuals. The objective method (sweep visually evoked potentials [sVEP]) has many parameters that may affect the measurement of VA or CS and previously these had not been studied systematically, especially in children. Therefore, a second purpose was to study the effects of these parameters on VA and contrast thresholds and to determine the parameters that give the most repeatable measurements and the greatest number of viable readings in children, to be compared to previous data obtained in adults. Methods: The effect of five criteria (C0-C4) for choosing the endpoint for the regression line fitting and three luminance levels (25, 50, and 100 cd/m2) on the sVEP VA and contrast thresholds (at 1 and 8 cpd) was investigated in six 6-8 year old children. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. C0 was derived from the sVEP software (PowerDiva), C1 used the best fit by eye to determine the range over which the regression line was fitted, C2 used the data point between signal peak and the last data point with an SNR ≥ 1, C3 was similar to C2 but was defined so that the threshold should be within the sweep range, and C4 was similar to C2 except that the SNR should not fall below one at any point within the range used for the regression line fitting. The effects of two electrode placements, three temporal frequencies (6, 7.5, and 10 Hz), sweep direction (low to high and high to low), presence or absence of a fixation target, three stimulus areas (6, 4, and 2° for VA and 15, 10, and 6° for contrast thresholds) and three sweep durations (10, 15, and 20 sec) on VA and contrast thresholds (at 1, 4, or 8 cpd) measured with sVEP were also investigated in six 6-8 year-old children and six adults with normal vision. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. The sVEP parameters that were found to give the best threshold measurements were employed in a cross sectional study of the development of VA and CS. In this study the objective sVEP technique and two psychophysical techniques were used. The psychophysical techniques were comprised of a two-alternative forced choice (2AFC) staircase for measuring VA and contrast thresholds and signal detection theory (SDT) for measuring contrast threshold. Crowded and uncrowded logMAR VA were also measured with a Bailey-Lovie logMAR chart. The study included three age groups (6-8, 9-12 year olds and adults). The criterion employed by each age group as indicated by the SDT was compared. Results: There was a significant effect of the criterion for choosing the endpoint for the regression line fitting (p < 0.05) on all the measures and a significant effect of luminance (p = 0.036) on contrast threshold at 1 cpd. Criterion C2 (in which the range for the regression line fit was defined to include all the data between the signal peak and the last data point [furthest from the peak] with an SNR ≥ 1) consistently gave more viable readings and better thresholds (i.e. higher VA and lower contrast thresholds) than the other criteria. Also C2 was the best criterion in terms of repeatability in children, and repeatability and validity in adults (Yadav et al., 2009). The luminance of 25 cd/m2 gave higher contrast thresholds than 50 or 100 cd/m2. There was a significant effect of temporal frequency on the number of viable readings for VA (p < 0.0001) and for contrast thresholds (p = 0.0001), with more viable readings at 7.5 Hz than at either 6 or 10 Hz. The adults gave more readings with the fixation target than without it (p = 0.04) for contrast threshold at 1 cpd. The smallest stimulus area used gave rise to fewer viable readings in both adults and children (p = 0.022 for VA and 0.0001 for contrast threshold). The other parameters (electrode placement, sweep direction and sweep duration) did not result in significant differences. There was a significant effect of age on crowded (p = 0.0001) and uncrowded (p < 0.0001) VA. The 6-8 year olds gave poorer VA than the 9-12 year olds or adults for both crowded and uncrowded VA. For the grating VA (sVEP and 2AFC staircase) there was a significant effect of age (p = 0.002). The 6-8 year olds had poorer VA than the 9-12 year olds or adults. For contrast threshold at 1 cpd, a significant effect of age was found for the 2AFC (p = 0.008) and SDT (p = 0.0003). The 6-8 year olds gave poorer contrast thresholds than adults with each procedure. For contrast thresholds at 8 cpd, there was a significant effect of age with the 2AFC staircase (p = 0.036). The 6-8 year olds gave poorer contrast thresholds than the 9-12 year olds. For SDT, there was a significant effect of age on criterion (p < 0.05), with adults being more likely to say “no” in the yes-no SDT procedure than both the 6-8 year olds and the 9-12 year olds for contrast threshold at 1 cpd. Adults were also more likely to say “no” than the 9-12 year olds for contrast thresholds at 8 cpd. Conclusions: This thesis has shown that VA and CS are not adult-like until the age of 9-12 years by these measures and that children do show differences in criterion compared to adults in psychophysical testing. This difference in criterion indicates the use of SDT or force-choice procedures to avoid this problem in any psychophysical developmental study. It has also shown that criterion for choosing the endpoint for the regression line fitting in the sVEP technique has the greatest effect on VA and contrast thresholds measurements and viable readings, while the other sVEP parameters have little effect on the thresholds.

The natural world is filled with perfectly working, functional systems that are robust, accurate, and adaptable; this work takes favour with the aforesaid and presents a biologically inspired approach to computer vision; in particular on the subjects of image reconstruction, contrast enhancement and object recognition. The first half of this thesis takes an exploratory approach, on the example of image reconstruction, towards the understanding of the visual pathway from retina to the primary visual cortex (V1), investigating redundancy reduction, information preservation and contrast enhancement. The retina having approximately 130 million cells, is forced to discriminate with the incoming information. Programmed for concision, the primate eye encodes information with sparsity, yet remains information preserving by encoding only contrast. By reconstructing an image from its contrast map pairs using gradient descent least squares error minimization, this work has shown that information is preserved across the optic nerve channel despite sparsification of the input image presented on the photoreceptors. By mimicking the irregularities of the eye's receptive fields, it has been shown that the neural architecture along the visual pathway is robust and fault tolerant against irregularities - a general characteristic of the entire nervous system. Using non-linear and asymmetric gain control with the on-and off-centre contrast map pairs, it has been shown that the mean luminance of an image can be controlled and the aforesaid reconstruction can be used for straightforward enhancement; thus reducing contrast enhancement to a scaling operation over the contrast domain. This has further been successfully applied to colour image contrast enhancement using a number of different models, including the neuro-physiologically proven representation of colour opponency, in the form of colour opponent contrast maps. With the above work serving as a pre-processing stage, the second half of the thesis approaches the subject of object recognition; improving upon prior work in Sparse Representation Classification (SRC). Sparseness is a key feature of the brain's internal representation whereby it achieves its robustness and adaptability. This work replaces the mean square error measure for similarity comparison of images with a perceptually compatible structural error measure, as well as the conventional sparsifiers with a genetic algorithm of the original SRC algorithm. This has resulted in an improved recognition rate - owed in large part to a more effective similarity comparison and improved sparseness of the solution. The approaches to the troika of reconstruction, contrast enhancement and object recognition strengthen both premise and belief that biologically inspired vision is dually meritorious and warrants greater appreciation and study by the Computer Vision community at large; not to be discounted as is often done. The hope is this work proves a seed for future endeavours.

Yes
Adults with amblyopia ('lazy eye'), long-standing strabismus (ocular misalignment) or both typically do not experience visual symptoms because the signal from weaker eye is given less weight than the signal from its fellow. Here we examine the contribution of the weaker eye of individuals with strabismus and amblyopia with both eyes open and with the deviating eye in its anomalous motor position. The task consisted of a blue-on-yellow detection task along a horizontal line across the central 50 degrees of the visual field. We compare the results obtained in ten individuals with strabismic amblyopia with ten visual normals. At each field location in each participant, we examined how the sensitivity exhibited under binocular conditions compared with sensitivity from four predictions, (i) a model of binocular summation, (ii) the average of the monocular sensitivities, (iii) dominant-eye sensitivity or (iv) non-dominant-eye sensitivity. The proportion of field locations for which the binocular summation model provided the best description of binocular sensitivity was similar in normals (50.6%) and amblyopes (48.2%). Average monocular sensitivity matched binocular sensitivity in 14.1% of amblyopes' field locations compared to 8.8% of normals'. Dominant-eye sensitivity explained sensitivity at 27.1% of field locations in amblyopes but 21.2% in normals. Non-dominant-eye sensitivity explained sensitivity at 10.6% of field locations in amblyopes but 19.4% in normals. Binocular summation provided the best description of the sensitivity profile in 6/10 amblyopes compared to 7/10 of normals. In three amblyopes, dominant-eye sensitivity most closely reflected binocular sensitivity (compared to two normals) and in the remaining amblyope, binocular sensitivity approximated to an average of the monocular sensitivities. Our results suggest a strong positive contribution in habitual viewing from the non-dominant eye in strabismic amblyopes. This is consistent with evidence from other sources that binocular mechanisms are frequently intact in strabismic and amblyopic individuals.

Indiana University-Purdue University Indianapolis (IUPUI)
Alzheimer’s disease (AD) is the most common age-related neurodegenerative disease. Many researchers believe that an effective AD treatment will prevent the development of disease rather than treat the disease after a diagnosis. Therefore, the development of tools to detect AD-related pathology in early stages is an important goal. In this report, MRI-based markers of neurodegeneration are explored as biomarkers of AD. In the first chapter, the sensitivity of cross-sectional MRI biomarkers to neurodegenerative changes is evaluated in AD patients and in patients with a diagnosis of mild cognitive impairment (MCI), a prodromal stage of AD. The results in Chapter 1 suggest that cross-sectional MRI biomarkers effectively measure neurodegeneration in AD and MCI patients and are sensitive to atrophic changes in patients who convert from MCI to AD up to 1 year before clinical conversion. Chapter 2 investigates longitudinal MRI-based measures of neurodegeneration as biomarkers of AD. In Chapter 2a, measures of brain atrophy rate in a cohort of AD and MCI patients are evaluated; whereas in Chapter 2b, these measures are assessed in a pre-MCI stage, namely older adults with cognitive complaints (CC) but no significant deficits. The results from Chapter 2 suggest that dynamic MRI-based measures of neurodegeneration are sensitive biomarkers for measuring progressive atrophy associated with the development of AD. In the final chapter, a novel biomarker for AD, visual contrast sensitivity, was evaluated. The results demonstrated contrast sensitivity impairments in AD and MCI patients, as well as slightly in CC participants. Impaired contrast sensitivity was also shown to be significantly associated with known markers of AD, including cognitive impairments and temporal lobe atrophy on MRI-based measures. The results of Chapter 3 support contrast sensitivity as a potential novel biomarker for AD and suggest that future studies are warranted. Overall, the results of this report support MRI-based measures of neurodegeneration as effective biomarkers for AD, even in early clinical and preclinical disease stages. Future therapeutic trials may consider utilizing these measures to evaluate potential treatment efficacy and mechanism of action, as well as for sample enrichment with patients most likely to rapidly progress towards AD.