Dissertations / Theses on the topic 'Peripheral Refraction'

The aim of the present project was to analyse the link between peripheral posture, optics, optics and refractive error progression. Preliminary studies were conducted to ensure that peripheral aberrometry is valid for further analysis. The repeatability of the IRX-3 for peripheral aberrometry was asgood as for central measurements and the recalculation of elliptical pupils did not seem to be necessary for measurements up to 20 degrees eccentricity. Higher order aberration measurements werecomparable to other studies. Eye and head movements as well as working distance did not differ significantly between myopes and non-myopes. However, there was some evidence, that forward bending of the head during reading increases in association with higher refractive error progression rates. The link between central higher order aberrations and refractive error development was analysed by comparing higher order aberrations between isometropes and anisometropes. This analysisdid not show any significant association of higher order aberrations on the development, as no major differences were found between the two groups. For central vision, changes in biometric parameters during accommodation were analysed. It was found that biometric parameters change similarly in myopes and non-myopes. Peripheral accommodation was found to differ between myopes and emmetropes indicating that there might be an influence of peripheral refraction on myopisation. However, associationbetween peripheral refraction or peripheral aberrations and refractive error progression were not significant. The reason for this observation might be the low refractive error progression (0.04± 0.29 D in myopes and -0.12 ± 0.38 D in emmetropes) during one year in the study population.

Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.

Myopia is a refractive condition and develops because either the optical power of the eye is abnormally great or the eye is abnormally long, the optical consequences being that the focal length of the eye is too short for the physical length of the eye. The increase in axial length has been shown to match closely the dioptric error of the eye, in that a lmm increase in axial length usually generates 2 to 3D of myopia. The most common form of myopia is early-onset myopia (EO M) which occurs between 6 to 14 years of age. The second most common form of myopia is late-onset myopia (LOM) which emerges in late teens or early twenties, at a time when the eye should have ceased growing. The prevalence of LOM is increasing and research has indicated a link with excessive and sustained nearwork. The aim of this thesis was to examine the ocular biometric correlates associated with LOM and EOM development and progression. Biometric data was recorded on SO subjects, aged 16 to 26 years. The group was divided into 26 emmetropic subjects and 24 myopic subjects. Keratometry, corneal topography, ultrasonography, lens shape, central and peripheral refractive error, ocular blood flow and assessment of accommodation were measured on three occasions during an ISmonth to 2-year longitudinal study. Retinal contours were derived using a specially derived computer program. The thesis shows that myopia progression is related to an increase in vitreous chamber depth, a finding which supports previous work. The myopes exhibited hyperopic relative peripheral refractive error (PRE) and the emmetropes exhibited myopic relative PRE. Myopes demonstrated a prolate retinal shape and the retina became more prolate with myopia progression. The results show that a longitudinal, rather than equatorial, increase in the posterior segment is the principal structural correlate of myopia. Retinal shape, relative PRE and the ratio of axial length to corneal curvature have been indicated, in this thesis, as predictive factors for myopia onset and development. Data from this thesis demonstrates that myopia progression in the LOM group is the result of an increase in anterior segment power, owing to an increase in lens thickness, in conjunction with posterior segment elongation. Myopia progression in the EOM group is the product of a long posterior segment, which over-compensates for a weak anterior segment power. The weak anterior segment power in the EOM group is related to a combination of crystalline lens thinning and surface flattening. The results presented in this thesis confirm that posterior segment elongation is the main structural correlate in both EOM and LOM progression. The techniques and computer programs employed in the thesis are reproducible and robust providing a valuable framework for further myopia research and assessment of predictive factors.

The development of refractive errors remains of scientific and clinical interest down to the present day. This applies in particular to myopia which at higher levels is associated with an increased risk of ocular disease. In urban areas of Asia the prevalence of myopia has increased over the last few decades such that numbers have reached epidemic proportions. Multidisciplinary research efforts on the aetiology of myopia are ongoing. Among those the role of the retinal periphery in myopia has seen renewed interest in the past decade. This thesis describes a 4-year longitudinal study of refractive development in children and young adults that aimed to investigate factors associated with refractive error progression, particularly the relationship of central refraction with peripheral refractive state and ocular shape. For this project 140 subjects between 5 and 20 years were recruited. Their history and activities were assessed using a questionnaire. Non-cycloplegic central and peripheral (250 temporal) refraction as well as accuracy of accommodation were determined with the Shin-Nippon NVision-K 5001 autorefractor. Ocular dimensions were quantified with the Zeiss IOLMaster. This included peripheral ocular length measurements (190 superior, inferior, temporal, nasal) to infer ocular shape. Additionally amplitude of accommodation, dissociated heterophoria, visual acuity, contrast sensitivity, body height and pupillary distance were also determined.

The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.

Peripheral (out-to-the-side) vision is important for general mobility and tasks such as driving. This study evaluated appropriateness of testing methods used to measure peripheral optics and visual performance. Peripheral optics measurements depended on the instrument used to measure them. The choice of either head or eye movements to set up peripheral optics measurements was not critical, even when contact lenses were worn. The nature of targets, in terms of size and abrupt or gradual loss of contrast near the edge, affected peripheral detection. To measure peripheral contrast detection accurately in the presence of blur, fine spatial frequency sampling was required.

This thesis proposes a method to evaluate and quantify in a precise way the peripheral refraction induced by an ophthalmic lens. The motivation for this work stems from the progression of myopia and its possible causes; two of them are particularly key for this PhD: (a) Peripheral refraction of the eye may have an important role in the progression of myopia and (b) ophthalmic lenses are the compensating element more used in children and teenagers. These two elements fully justify the need for a reliable method to quantify the induced peripheral refraction by an ophthalmic lens. This method is based on two pillars: first, it must accurately assess the design of the ophthalmic lens and, second, it should consider what peripheral refractive pattern is acting, that is, without compensating element. The proposed method takes the advantages provided by the ray tracing strategies used in the classic design of ophthalmic lenses but applying them in parallel with amendments to evaluate the peripheral refraction. Thus, the simple scheme used in the classic design of ophthalmic lenses containing a remote sphere and a small aperture at the center of rotation of the eye becomes a scheme where the retina conjugate surface (RCS) and the nodal point of the eye play equivalent roles. In our case, the reference for ray tracing is the nodal point of the eye and the reference for measuring the induced peripheral refraction is the RCS. Ray tracing is based on a finite ray tracing (FRT) from the image space to the object space and on a generalized ray tracing (GRT) from object space to image space. Both have been implemented in a Matlab program and validated to provide a powerful tool for our purpose. GRT allows a quick and accurate assessment of the oblique astigmatism, ie the tangential and sagittal focal lens, in wide field of view considering accurately the lens design. This considers that each ray has a small wavefront associated traveling perpendicular to it. By GRT we are able to know how the wavefront shape changes when is propagated and refracted. Therefore, it is mandatory to have a locally description of the geometry of both the wavefront and the refractive surface at the point where the ray arrives to the refractive surface. This local description is determined by the normal and by the principal curvatures and directions of these surfaces at the point of interest; they can be obtained from a parametric description of the surface and then using Gaussian fundamental forms. This ray tracing procedure has been developed for the general case of any geometry to the surfaces of the ophthalmic lens and has been detailed for the case of an astigmatic lens. For calculating the induced peripheral refraction, a surface is modeled reflecting the peripheral refractive initial values before entering the lens; this is the aforementioned RCS. Two methods have been proposed to model this RCS. One is based on the trends observed in the different studies and uses three-dimensional surfaces power vectors associated with peripheral refraction. The second method uses experimental measurements obtained along four meridians of the retina to interpolate a surface. The expression of these surfaces by power vectors can easily be combined with the results obtained by tracing rays through the lens for the calculation of the induced peripheral refraction. We present in this manuscript some specific examples of how variations on the lens geometry modified the induced peripheral refraction. This opens up the possibility of custom designs ophthalmic lenses to prevent the progression of myopia.
Esta Tesis tiene como objetivo la propuesta de un método para la evaluación cuantitativa de la refracción periférica inducida en el ojo de un paciente por una lente oftálmica. La motivación del trabajo radica en la importancia de este fenómeno en el progresión de la miopía y sus causas. La existencia de una refracción periférica hipermetrópica se ha relacionado directamente con la progresión de la miopía, y las lentes oftálmicas son el elemento compensador preferenteen niños y adolescentes, los sujetos más relevantes en cuanto al control de la progresión de l amiopía, en sí misma y como antesala d eotros problemas oculares más graves. Hasta la realización de esta Tesis no existía un método preciso, próximo a los métodos convencionales del diseño de lentes oftálmicas, que permitiera el cálculo de la refracción periférica inducida por la lente oftálmica y el análisi de los diseños de lente utilizados. Dicho diseño debe considerar tanto los efectos asociados a a óptica y la geometría del ojo, como al propio diseño de la lente compensadora. El método que se propone sigue una metodologia próxima a la del diseño convencional de lentes oftálmicas, sustituyendo el rol del centro de rotación del ojo por el de su punto nodal, y el rol de la esfera del remoto por lo qque se ha denominado la superfície conjugada de la retina (RCS, de retinal conjugate surface, en el texto). Con este enfoque se han implementado algoritmos detallados de trazado de rayos finito y generalizado que permiten el trazado detallado de rayos en un conjunto de direcciones alrededor de la fóvea. Los algoritmos de trazado generalizado permiten el análisis de lentes oftálmicas de manera más eficiente que el trazado intensivo típico del software de diseño óptico, utilizando el concepto de trazado de frente d eonda, que analiza las deformaciones del frente de onda que acompaña a un rayo principal. Dichos algoritmos se han implementado y validado para un conjunto de lentes oftálmicas de diferentes geometrías en un software científico estándard (Matlab(R)) como parte de los trabajos desarrollados en esta Tesis. Mediante el uso de los algoritmos descritos es posible calcular la superficie refractada que induceuna lente oftálmica. A continuación se hen desarrollado modelos teóricos y experimentales para la RCS que permiten tener en cuanta la variabilidad de patrones de refracción periférica existente, y se ha propuesto el uso de vectores de potencia (M J0 y J45) para el cálculo de la refracción periférica inducida por la lente, mediante la combinación de la superficie refractada por la lente y la modelada para una determinada RCS. Se presentan casos para lentes esféricas, asféricas y astigmáticas, para ojos miopes y emétropes, y en condiciones de infra y sobre refracción, mostrando la potencialidad del método propuesto para diseñar lentes que compensen simultáneamente la refracción foveal y la periférica, que mediante el método propuesto podrán optimizarse simultáneamente.

Purpose: To study ???on??? and ???off-axis??? wavefront aberration of eyes of children and to determine the relationship with refractive error development. Methods: On and off-axis ocular aberrations of cyclopleged eyes of children (mostly 12 year olds) were measured and compared to data obtained from a group of mostly 6 year old children. Only data from the right eyes were analysed (pupil diameter=5 mm) and categorised into refractive error groups based on ???M???. Differences in ???on??? and ???off-axis??? aberrations between refractive and ethnic groups were analysed using univariate and multivariate analyses of variance with adjustment for multiple comparisons. Off-axis refraction was analysed using skiagrams and mean relative spherical equivalent. Results: Data from 1,636 12 year old children (mean age 12.6 ?? 0.4 years) was analysed. Lower order aberrations were the largest and higher order aberrations contributed to only 25% of the wavefront. There were no differences in the amount of total higher orders between refractive groups. Of the individual higher orders, spherical aberration was greater in hyperopic eyes (0.07 ?? 0.06 ??m) in comparison to emmetropic and myopic eyes (0.05 ?? 0.04 ??m and 0.05 ?? 0.04 ??m) (p<0.001). Myopic eyes had more positive values of Z(3,-1) (p<0.05). Similar results were obtained for the 1,364 6 year old children (mean age 6.7 ??? 0.4 years). Despite East Asian children being more myopic than other ethnic groups (p<0.01), there were no differences in higher orders except for low hyperopic East Asian eyes presenting with higher levels of positive spherical aberrations (p<0.001). When compared to the fovea, off-axis myopic eyes had hyperopia (0.55 to 1.66 D) and emmetropes and hyperopes had myopia (0.10 to -2.00 D). Astigmatism and defocus were the dominant off-axis aberrations. The magnitude of higher order aberrations (mostly 3rd orders) increased with eccentricity but was similar across refractive error groups. Conclusions: Myopic eyes do not have abnormal or excessive levels of on and off-axis higher order aberrations but had patterns of off-axis refraction that may be associated with progression. Considerable inter-subject variability in higher order aberrations was seen for all refractive groups. However, their magnitude was small and suggests that any impact on the optical quality of the eye is negligible.

Orthokeratology (OK) contact lenses have shown propensity for slowing down the worsening of myopia in children and young adults, with only some understanding of the mechanism. This thesis examined eye muscle coordination and focussing in OK contact lens wear; outcomes were consistent with a lower myopia progression risk and improved visual comfort compared to standard spectacles and soft contact lenses. These findings have relevance for patient acceptance, clinical management protocols and understanding OK's optical impact on the visual system of the young myope.

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.

La cirugía refractiva corneal corrige los errores refractivos modificando la curvatura de la córnea. Después de la cirugía de la miopía con técnica LASIK, se ha observado un aplanamiento central inesperado de origen biomecánico y un encurvamiento periférico. El objetivo de este trabajo fue estudiar la relación entre ambos fenómenos y otros parámetros oculares. Se realizó un estudio retrospectivo de una serie quirúrgica, utilizando las topografías tangenciales diferenciales. El encurvamiento se caracterizó mediante tres parámetros: incremento de potencia, diámetro de la zona de mayor valor (anillo) y ángulo del gradiente periférico. Un estudio prospectivo analizó su presencia post-ablación en cuatro tipos de modelos esféricos experimentales sin respuesta biomecánica. El encurvamiento periférico se situó entre la zona óptica y la zona de transición, con un ligero desplazamiento lateral debido al ángulo kappa. No se halló correlación con el aplanamiento central inesperado. Tiene una correlación positiva y significativa con el gradiente teórico y con la edad. En los modelos experimentales, se presentó un anillo de encurvamiento periférico
Corneal refractive surgery corrects refractive errors by modifying the corneal curvature. After myopia surgery with LASIK, a central unexpected flattening of biomechanical origin and a peripheral steepening have been observed. The aim of this work was to study the relation between both facts and other ocular parameters. A retrospective study of a surgical series was done using the tangential differential topography. Steepening was characterized by three parameters: increase of power, diameter of the zone of major value (ring) and the angle of the peripheral gradient. A prospective study analyzed post-ablation peripheral steepening in four types of spherical experimental models without biomechanical response. The peripheral steepening was placed between the optical zone and the transition zone, with a light lateral displacement due to angle kappa values. No correlation with the central unexpected flattening was found, whereas it has a positive and significant correlation with the theoretical gradient and with the age. In the experimental models, a ring of peripheral steepening was present.

碩士
中山醫學大學
視光學系碩士班
105
Myopia has now become a global public health issue. In Taiwan, the prevalence of myopia in children has been up to more than 80%. In many other countries, the prevalence of myopia and high myopia is rising at an alarming rate as well, with significant increases in the risks for vision impairment from pathological conditions associated with high myopia, including macular degeneration, cataract and glaucoma. With the increase in myopia, the risk of visual disability also increased To date, the following have been used for myopia control: medication, (such as Atropine eye drops), spectacles, contact lens and orthokeratology. Research involving many animal species has demonstrated that refractive condition plays a role in vision development, while the imaging position of peripheral retina has tremendous influence on myopia progression. Thus, a myopia control strategy taking into account the peripheral refraction is likely to be more effective. The purpose of this study is, using ASAP optical software, to create a spectacle lens model which is able to change peripheral refractive condition, and to analyze the image and the luminous flux in the retina. The potentials of the procedure is presented as the three design examples of -2.50D, -5.00D and -7.50D. The results show that this spectacle lens model is able to change peripheral refractive errors and, in the future, may be used to reduce progression of myopia.

碩士
中山醫學大學
生物醫學科學學系碩士班
103
Purpose: To compare the patterns of relative peripheral refractions, astigmatic refractions and peripheral accommodative between myopic children who are currently on atropine treatment for controlling their myopia progression and those who don’t use atropine. Methods: Chinese children (n =209) aged 7 to 12 years participated in the study, of which 106 subjects were classified into the atropine group and 103 subjects were in the non-atropine group. According to their refractive errors, the subjects were also classified into three groups: emmetropes (SE: +0.50 to -0.50 D), low myopes (SE: -0.50 to -3.00 D) and moderate myopes (SE: -3.00 to -6.00 D). The central and peripheral refractions along the horizontal meridian (for both nasal and temporal fields) within30 degrees were measured at 4 m and 33 cm Results: There were no statistically significant differences between the three refractive groups in the nasal and temporal retina for the spherical equivalent (SE) and astigmatism. The atropine group showed significant relative myopia in the temporal 30ﾟ field in spherical equivalent for the emmetropic group (P=0.01). In low myopic children, the atropine group had significant relative myopia in the nasal 30ﾟand temporal 30ﾟfield in spherical equivalent (P=0.047, P=0.021), and it is also observed at nasal 20ﾟ and 30ﾟin spherical equivalent and J45 astigmatism temporal field for the moderate myopic group(P=0.023, P=0.008, P=0.007). Atropine group showed significant relative myopia in the J45 astigmatism temporal 30ﾟfield and SE for the emmetropic group (P=0.011). In low myopic children, the atropine group had significant relative myopia in the J45 astigmatism temporal field (P=0.001), and it is also observed at nasal 20ﾟ and 30ﾟ field in spherical equivalent for the moderate myopic group (P=0.012, P=0.013). The atropine group showed significant relative accommodative lag in the temporal 30ﾟfield in peripheral accommodation for the emmetropic group (P=0.009). The accommodative response, the atropine group had significant relative myopia in the nasal 30ﾟ field in low myopic eye(P=0.044). Conclusions: Significant differences between with and without atropine groups in relative peripheral refraction were found for emmetropic, low myopic and moderate myopic eyes. The present findings suggest that the eyes which received atropine may be less prolate and thus help explain the mechanism of myopia progression control in myopic children. Atropine can cause accommodative lag in emmetropic and low myopic.

碩士
中山醫學大學
視光學系碩士班
105
Purpose To investigate the changes in relative peripheral refractive error (RPRE) with and without the intervention of accommodation. Methods The 19 subjects aged 18 to 30 years participated in this study, including 11 emmetropia eyes (spherical equivalent > -1.00 D) and 23 myopia eyes (SE≤ -1.00 D). Peripheral refractions were analyzed from the central to 25° for the temporal and nasal retina at both distance and near. To quantify the changes in relative peripheral refraction under accommodation, conventional sphero-cylindrical refractive error was converted into power vectors M (spherical equivalent), J0, and J45 for data analysis. Results When accommodation was used, there was an increasing trend in RPRE(M) for all the angles and significant differences were found at N25 (p = 0.001), N10 (p = 0.033), T10 (p = 0.034), T15 (p = 0.001), T20 (p < 0.0005), T25 (p < 0.0005). For J0, RPRE was also increased, which suggested that it changed from against-the-rule into with-the-rule astigmatism at N25 (p < 0.0005), N20 (p < 0.0005), N15 (p < 0.0005), N10 (p < 0.0005), T15 (p = 0.001), T20 (p < 0.0005), T25 (p < 0.0005). Conclusion The relative peripheral refractive errors changed under accommodation condition. It shifted from relative myopia to relative hyperopia for the temporal retina, and also from against-the-rule astigmatism to with-the-rule astigmatism. These results may help explain the association between relative peripheral refraction, accommodation and myopia development.

PhD Thesis in Sciences - Specialty in Physics
Myopia affects approximately 25% of the World population, being a public health concern due to the socioeconomic impact and to the risk of vision loss related to other co-morbidities. If current trends continue, half the world’s population (almost 5 billion) will be short-sighted in just over three decades, with one-fifth of those expected to have a significantly increased risk of blindness. Clinical evidence from animal models and human clinical trials seems to indicate that the peripheral refraction pattern plays an important role in the regulation of eye growth. Lower progression rates have been reported over the last years in myopic children wearing orthokeratology (ortho-k) or special design contact lenses, when compared with those wearing traditional ophthalmic lenses. To date, the only justification for this effect seems to lie in the significant myopization effect induced by these alternative forms of correction beyond the foveal area, but despite the moderate results obtained researcher’s still lack knowledge of the exact mechanism behind this effect and why does it work better in some subjects than others. In this thesis a frame work was developed to model the possible impact of the eye’s posterior shape and the optical changes produced by ortho-k in myopia progression. Optical modeling and biometric eye length measures were used to calculate the retinal contour in 55 myopic subjects, with an accuracy of tenths of a micron. The results show that there is large inter-subject variability in the shape of the posterior pole, even among subjects with similar refractive errors. An exhaustive characterization of the ortho-k cornea was also conducted to analyze the main morphological, topographical and optical changes induced by these treatments and their possible implications in the peripheral refractive error and accommodative response. The results suggest that the reported effects in the retention of eye growth, supposedly due to the peripheral myopization produced by ortho-k treatments, might be dependent on pupil size. Optical quality analysis revealed that although the increase in positive spherical aberration is the main cause of the loss of retinal image quality in the unaccommodated eye after ortho-k, it also seems to have a positive effect, as it extends the depth of field of the eye and may contribute to a better image quality in subjects with accommodative lag during high contrast near vision tasks.
A actual prevalência mundial da Miopia (25%) é já considerada um problema de saúde pública devido ao impacto sócio-económico e ao risco de perda de visão relacionada com outras co-morbidades. Se as tendências actuais se mantiverem, metade da população mundial (quase 5 mil milhões) será míope daqui a pouco mais de três décadas, e cerca de um quinto deverá ter um aumento significativo do risco de cegueira. Evidências clínicas baseadas em modelos animais e ensaios clínicos com pacientes humanos parecem indicar que o padrão da refracção periférica desempenha um papel importante na regulação do crescimento axial do olho. Níveis mais baixos de progressão têm sido reportados ao longo dos últimos anos em grupos de crianças míopes corrigidas com ortoqueratologia (orto-k) ou lentes de contacto com geometrias especiais, em comparação grupos de controle compensados com lentes oftálmicas tradicionais. Até à data, a única justificação plausível para estes resultados parece residir no efeito miopização periférica induzido por essas formas alternativas de correção para além da área foveal, mas apesar dos resultados moderados obtidos ainda falta conhecimento do exacto mecanismo por trás deste efeito e porque o efeito é maior em alguns indivíduos que em outros. Nesta tese foi desenvolvido um quadro de trabalho com o objectivo de modelizar o possível impacto da forma do polo posterior do olho e a das alterações estruturais induzidas pela ortoqueratologia na progressão da miopia. O contorno da retina de 55 indivíduos míopes foi calculado com recurso a modelização óptica e medidas biométricas do comprimento do olho, com uma precisão de décimos de micras. Os resultados demonstram que existe uma grande variabilidade inter-individual na forma do pólo posterior do olho, mesmo entre indivíduos com erros refractivos semelhantes. Foi também realizada uma caracterização exaustiva da córnea pós orto-k, com o objectivo de analisar as principais alterações morfológicas, topográficas e ópticas induzidas por estes tratamentos e as suas possíveis implicações no erro refractivo periférico, assim na resposta acomodativa. Os resultados sugerem que os relatos de uma menor taxa de progressão da miopia em olhos tratados com ortok, supostamente devido à miopização periférica produzida por estes tratamentos, pode ser dependente do tamanho da pupila. A análise da qualidade óptica revelou que, embora o aumento da aberração esférica positiva após orto-k seja a principal causa da diminuição da qualidade da imagem retiniana no olho desacomodado, também aparenta ter um efeito positivo na extensão da profundidade de campo, o que poderá contribui para um aumento da qualidade da imagem retiniana em indivíduos com atraso acomodativo durante tarefas de alto contraste em visão próxima.

PhD Thesis in Optometry and Vision Sciences
Myopia is becoming a public health concern, with well documented evidence of rapid increasing prevalence in Asia, Europe and the United States of America. Further concerns arise from the fact that myopia onset takes place at an earlier age and progresses over a superior number of years, resulting in higher degrees of myopia in adulthood thus presenting an increased risk of visual loss related with severe eye disease. Over the past 10 years, contact lenses have become an essential device in the strategies to control myopia progression and there is now evidence that different contact lens designs are effective in slowing-down myopia progression. Considering that such lenses have the potential to change the pattern of peripheral refraction and the depth of focus, the present thesis was developed with the aims of investigating the effect of different contact lens devices in the patter of axial and peripheral refractive error in young adults and their effect in the accommodative function. The methods used included axial and peripheral refractive evaluation with an open field autorefractor; a system linked to autorefractometer to dynamic refractive data collection allowing to measure accommodative response and pupil size; a Hartmann-Shack (H-S) aberrometer was also used to determine axial optical aberrations and also a manufactured system linked to H-S to provide peripheral aberrations measurement. We performed 7 trials involving 308 healthy non-myopic and myopic subjects. Results show myopic shift at peripheral refractive pattern of myopic eyes by wearing dominant design MFCL. Peripheral ocular aberrations in eyes fitted with MFCL also were modified; the trend was to increase, depending of design but mainly spherical aberration and coma. Accommodative function of unaided young eyes revealed LAG, mainly at higher accommodative demand. The accommodative facility and accuracy were not significantly modified by wear of MFCL independently of design. Comparison between methods of measuring peripheral refraction revealed that there were no differences between measurements using eye rotation or head rotation with and without MFCL; also were comparable measurements by using an open-field autorefractometer or an adapted H-S aberrometer. The main conclusions were that peripheral refraction and peripheral aberrations could be modified differently by different design of MFCL. Accuracy and amount of accommodation not changed by wear of neither design of MFCL tested.
A miopia é considerada um problema de saúde pública, mostrando evidências bem documentadas de prevalência na Asia, Europa e Estados Unidos da América. A razão de se levantar maior preocupação no aparecimento da miopia em idades precoces resulta do facto de havendo progressão durante um maior período de tempo a miopia ira ser mais alta na idade adulta, o que resulta em risco de perda severa da visão. Nos últimos 10 anos, as lentes de contacto têm mostrado ser um dispositivo essencial na perspetiva de controlo da progressão da miopia, havendo atualmente várias evidências de eficácia, dependendo do tipo de lente. Considerando que as lentes de contacto representam potencial para alterar o padrão de refração periférica (RP) e profundidade de foco, esta tese foi desenvolvida com os objetivos de investigar o efeito de diferentes tipos de lentes de contacto no padrão refrativo axial e periférico assim como avaliar o seu efeito na função acomodativa. Os métodos usados incluem a avaliação axial e periférica através de um autorefractómetro de campo aberto; um sistema acoplado ao autorefractómetro construído para permitir a medida dinâmica da refração permitindo a automática medida da função acomodativa e do diâmetro pupilar; um aberrómetro Hartmann-Shack (H-S) para determinar as aberrações axiais; assim como um dispositivo experimental acoplado ao H-S que permitiu a determinação das aberrações periféricas. Foram realizados 7 estudos envolvendo 308 indivíduos saudáveis míopes e não-míopes. Os resultados mostram miopização periférica nos olhos adaptados com lente de contacto multifocal (LCMF) de desenho dominante. As aberrações oculares periféricas avaliadas em olhos adaptados com LCMF também revelaram alterações; a tendência foi no sentido do aumento, dependendo do desenho óptico, principalmente aberração esférica e coma. A função acomodativa em olhos jovens sem LC manifestou LAG, principalmente para as vergências mais reduzidas. A resposta acomodativa e a sua precisão não se alteraram com o uso LCMF, independentemente do desenho óptico. Realizaram-se também comparações entre métodos de avaliação da RP, verificando-se que as medidas realizadas através da rotação da cabeça ou dos olhos são comparáveis, com e sem LCMF; assim como as medidas realizadas através do autorefractómetro de campo aberto ou aberrómetro H-S adaptado. As principais conclusões são que a RP e as aberrações periféricas podem ser alteradas com LCMF, dependendo do desenho. A função acomodativa não se mostrou variar com o uso de diferentes desenhos de LCMF.

AIM: The aim of the study was to determine, objectively and non-invasively, whether changes in accommodative demand modify differentially the peripheral refraction in emmetropic and myopic human eyes. METHODS: Forty subjects (19 male, 21 female) aged 20-30 years (mean 22.7 (SD 2.8) years), 21 emmetropes (mean spherical equivalent refractive error (MSE) -0.13 (SD 0.29) D) and 19 myopes (MSE -2.95 (SD 1.76) D) participated in the study. Ametropia was corrected with soft contact lenses (etafilcon A, 58% water content). Subjects viewed monocularly a stationary, high contrast (85%) Maltese cross at 0.0, 1.0, 2.0 and 3.0 D of accommodative demand and at 0, 10, 20 and 30 degrees field angle (nasal and temporal) through a +3.0 D Badal optical system. Static recordings of the accommodation response were obtained for each accommodative level, at each field angle, with an objective, open-view, infrared optometer. RESULTS: Peripheral mean spherical equivalent (M) data showed that the emmetropic cohort exhibited relative myopic shifts into the periphery, while the myopic group showed hypermetropic shifts. Increasing accommodative demand did not alter the peripheral refractive profile in either the temporal (p = 0.25) or nasal (p = 0.07) periphery with no differential accommodative effect between refractive groups in either the temporal (p = 0.77) or nasal (p = 0.73) field. Significant shifts in the J(0) astigmatic component were seen in the temporal (p<0.0005) and nasal (p<0.0005) fields with increasing eccentricity. Interaction effects between eccentricity and accommodative demand illustrated that increasing accommodative demand significantly altered the peripheral refractive profile in the temporal J(0) astigmatic component (p<0.0005). The nasal periphery, however, failed to show such an effect (p = 0.65). CONCLUSIONS: Alterations in peripheral refraction augmented by changes in ocular accommodation are relatively unaffected by refractive error for young, healthy human eyes.

碩士
中山醫學大學
生物醫學科學學系碩士班
104
Purpose: This study aims to determine whether the relative peripheral refractive errors and the shape of retina by high-resolution three-dimensional magnetic resonance imaging in high myopia. Methods: Sixteen young adults with high myopia (over＞6.00 D) and nineteen emmetropic ( +0.50 to -0.50 D) young adults were investigated. An open-field auto-refractor was used to measure on- and off-axis refractions in horizontal meridian every 3° out to 30° in nasal and temporal retina, and in vertical meridian every 3° out to 12° in superior and inferior retinal. Axial ocular dimensions were measured by A-scan ultrasonography. Axial (horizontal through middle of eye), sagittal (vertical through axis) and tangential (horizontal through axis) sections were taken with a magnetic resonance imaging. Result: High myopic subjects had greater relative hyperopia in the periphery 30° temporal (+2.48 ± 0.90 D),30° nasal (+2.68 ± 1.16 D), 9° Superior (+0.64 ± 0.58 D) and 12° Inferior (+0.65 ± 0.63 D), indicating a prolate ocular shape (longer axial length than equatorial diameter), compared with relative peripheral myopia and an oblate shape (broader equatorial diameter than axial length) for emmetropes 30° temporal (-1.64 ± 0.42 D)and 30° nasal(-1.39 ± 0.44 D), 9° Superior (- 0.55 ± 0.27D) and 12° Inferior (-0.860 ± 0.29 D) .High myopic eyes showed much larger in all three dimensions, but more so in length (26.15 ± 1.05 mm) than in height (24.59 ± 0.87 mm) and more so in height than in width (24.41 ± 1.21mm). Emmetropic eyes showed the similar in three dimensions (height is 23.58 ± 0.61 mm, length is 23.40 ± 0.68 mm, and width is 23.19 ± 0.90 mm). In high myopic groups, the curvature of retina showed a significant negative correlation with the relative peripheral refraction(Temporal：Pearson r = -0.459；P＞0.01；Nasal：Pearson r = -0.277；P = 0.011；Superior：Pearson r = -0.066；P = 0.679；Inferior：Pearson r = -0.260；P = 0.096). Conclusions: In this study, the emmetropic groups showed relative peripheral myopic refrction and oblate ocular shape；The high myopic groups showed relative peripheral hyperopic refraction and prolate ocular shape. In high myopic eyes are negative correlation with the curvature of retina and relative peripheral refraction.

碩士
國立中正大學
光機電整合工程研究所
106
Myopia is considered an urgent public health problem due to the impact of the global population and the burden of visual disability. An estimated 1.5 billion people were affected in 2010. Myopia is the most common cause of permanent visual impairment and is expected to increase by nearly 5 billion by 2050. Based on the peripheral refractive theory, this study designed a contact lens that can change the peripheral refraction of the retina,and established a measurement system that can measure the refractive state of the eyeball. The ASAP optical simulation software was used to analyze the retina under different refractive conditions. The image, together with the optimization, calculates the refractive power vector as the basis for correcting the effect. The purpose of this study is to cause relative myopia or peripheral hyperopia to control the growth of the axial growth of the eye to control the development of myopia. According to the results, the fourth-order spherical aberration peripheral refractive lens model constructed in this study is used, which has a good corrective effect on myopia control. Keywords: peripheral refraction, lens design, myopia control

碩士
逢甲大學
電機工程學系
104
This paper proposes a multi-layer structure of RGP contact lenses design for peripheral refractive error correction of myopia. The structure is a combination of free-form、even-aspherical and biconic surface. This article describes contact lenses design procedure to correct visual aberration, such as defocus、coma and astigmatism, from the 〖30〗^° temporal side to the 〖30〗^° nasal side. Compared to a conventional contact lens, our design can simultaneously correct the defocus on central field and peripheral field on the retina. It expands the clear visual scope and avoids the further deterioration of myopia. The greatest feature of this design is that we combine three layers together. The first surface is biconic for correcting astigmatism, the second is even-aspherical for correcting high-order aberrations, and the third surface is of free-form to correct off-axis defocus at retina, the last surface is spherical with a radius of curvature matching the front surface of cornea. This design provides more flexibility and optimizable parameters to correct high order aberrations, while correcting the defocus on peripheral field. Thus achieve a better visual image quality, finally field at 0°、±10°、±20°、±30° which cutoff frequency is sequentially 110lp/mm, 35lp/mm, 20lp/mm and 15lp/mm of MTF values have reached 0.3.

碩士
中山醫學大學
生物醫學科學學系碩士班
101
Purpose: To determine and analyze the relative peripheral refractive error (RPRE) in the myopization of elementary school students in Taiwan. Methods: 395 healthy Grades 1 to 6 (from 7-12 years of age) students with no ocular diseases participated in the study. The refractive error ranged from +2.00 to -9.00 D with an astigmatism of ≦ 2.00 D and the best corrected visual acuity, ≧20/20. Open-field auto-refraction was conducted with the visual target located at 6m in the central/foveal position and also horizontally relative to the fovea, at 10o, 20o, and 30o, both nasally and temporally. Statistical analysis was performed between the Grades and also among the refractive groups - the latter divided into hyperopia, emmetropia, mild myopia (up to -0.50D), moderate myopia (-2.01 to -4.00D), and high myopia (worse than -4.01D). Results: The spherical equivalent (SE) of the RPRE showed significant difference between the Grades (F=78.833, p<0.001), most notably that between the 5th and the 6th Grades, but no difference was noted between the two genders or the extent of astigmatism (either J0 or J45). The SE of the RPRE was also significantly different between each refractive group, and between different retinal positions. The latter indicated, temporally: T10o: F= 18.814, p <0.001; T20o: F = 24.048, p <0.001; and T30o: F = 26.994, p <0.001; and nasally: N10o: F = 10.769, p <0.001; N20o: F = 8.351, p <0.001; and N30o: F = 17.597, p <0.001 , and the most pronounce change was from T20 o to T30 o. In addition, the RPRE of the hyperopic group exhibited myopic refractive patterns, while the myopic groups, hyperopic refractive patterns. Conclusions: Our study has demonstrated that the RPRE on the temporal side had more variability than the nasal side. This result is opposite to previous findings by others. In terms of myopization, the interaction of both developmental and peripheral variables would appear to decide the outcome of the RPR error. This information can form the basis for the future design of optimal myopic correction.