Dissertations / Theses on the topic 'Higher order aberration'

The depth of focus (DOF) can be defined as the variation in image distance of a lens or an optical system which can be tolerated without incurring an objectionable lack of sharpness of focus. The DOF of the human eye serves a mechanism of blur tolerance. As long as the target image remains within the depth of focus in the image space, the eye will still perceive the image as being clear. A large DOF is especially important for presbyopic patients with partial or complete loss of accommodation (presbyopia), since this helps them to obtain an acceptable retinal image when viewing a target moving through a range of near to intermediate distances. The aim of this research was to investigate the DOF of the human eye and its association with the natural wavefront aberrations, and how higher order aberrations (HOAs) can be used to expand the DOF, in particular by inducing spherical aberrations ( 0 4 Z and 0 6 Z ). The depth of focus of the human eye can be measured using a variety of subjective and objective methods. Subjective measurements based on a Badal optical system have been widely adopted, through which the retinal image size can be kept constant. In such measurements, the subject.s tested eye is normally cyclopleged. Objective methods without the need of cycloplegia are also used, where the eye.s accommodative response is continuously monitored. Generally, the DOF measured by subjective methods are slightly larger than those measured objectively. In recent years, methods have also been developed to estimate DOF from retinal image quality metrics (IQMs) derived from the ocular wavefront aberrations. In such methods, the DOF is defined as the range of defocus error that degrades the retinal image quality calculated from the IQMs to a certain level of the possible maximum value. In this study, the effect of different amounts of HOAs on the DOF was theoretically evaluated by modelling and comparing the DOF of subjects from four different clinical groups, including young emmetropes (20 subjects), young myopes (19 subjects), presbyopes (32 subjects) and keratoconics (35 subjects). A novel IQM-based through-focus algorithm was developed to theoretically predict the DOF of subjects with their natural HOAs. Additional primary spherical aberration ( 0 4 Z ) was also induced in the wavefronts of myopes and presbyopes to simulate the effect of myopic refractive correction (e.g. LASIK) and presbyopic correction (e.g. progressive power IOL) on the subject.s DOF. Larger amounts of HOAs were found to lead to greater values of predicted DOF. The introduction of primary spherical aberration was found to provide moderate increase of DOF while slightly deteriorating the image quality at the same time. The predicted DOF was also affected by the IQMs and the threshold level adopted. We then investigated the influence of the chosen threshold level of the IQMs on the predicted DOF, and how it relates to the subjectively measured DOF. The subjective DOF was measured in a group of 17 normal subjects, and we used through-focus visual Strehl ratio based on optical transfer function (VSOTF) derived from their wavefront aberrations as the IQM to estimate the DOF. The results allowed comparison of the subjective DOF with the estimated DOF and determination of a threshold level for DOF estimation. Significant correlation was found between the subject.s estimated threshold level for the estimated DOF and HOA RMS (Pearson.s r=0.88, p<0.001). The linear correlation can be used to estimate the threshold level for each individual subject, subsequently leading to a method for estimating individual.s DOF from a single measurement of their wavefront aberrations. A subsequent study was conducted to investigate the DOF of keratoconic subjects. Significant increases of the level of HOAs, including spherical aberration, coma and trefoil, can be observed in keratoconic eyes. This population of subjects provides an opportunity to study the influence of these HOAs on DOF. It was also expected that the asymmetric aberrations (coma and trefoil) in the keratoconic eye could interact with defocus to cause regional blur of the target. A dual-Badal-channel optical system with a star-pattern target was used to measure the subjective DOF in 10 keratoconic eyes and compared to those from a group of 10 normal subjects. The DOF measured in keratoconic eyes was significantly larger than that in normal eyes. However there was not a strong correlation between the large amount of HOA RMS and DOF in keratoconic eyes. Among all HOA terms, spherical aberration was found to be the only HOA that helped to significantly increase the DOF in the studied keratoconic subjects. Through the first three studies, a comprehensive understanding of DOF and its association to the HOAs in the human eye had been achieved. An adaptive optics system was then designed and constructed. The system was capable of measuring and altering the wavefront aberrations in the subject.s eye and measuring the resulting DOF under the influence of different combination of HOAs. Using the AO system, we investigated the concept of extending the DOF through optimized combinations of 0 4 Z and 0 6 Z . Systematic introduction of a targeted amount of both 0 4 Z and 0 6 Z was found to significantly improve the DOF of healthy subjects. The use of wavefront combinations of 0 4 Z and 0 6 Z with opposite signs can further expand the DOF, rather than using 0 4 Z or 0 6 Z alone. The optimal wavefront combinations to expand the DOF were estimated using the ratio of increase in DOF and loss of retinal image quality defined by VSOTF. In the experiment, the optimal combinations of 0 4 Z and 0 6 Z were found to provide a better balance of DOF expansion and relatively smaller decreases in VA. Therefore, the optimal combinations of 0 4 Z and 0 6 Z provides a more efficient method to expand the DOF rather than 0 4 Z or 0 6 Z alone. This PhD research has shown that there is a positive correlation between the DOF and the eye.s wavefront aberrations. More aberrated eyes generally have a larger DOF. The association of DOF and the natural HOAs in normal subjects can be quantified, which allows the estimation of DOF directly from the ocular wavefront aberration. Among the Zernike HOA terms, spherical aberrations ( 0 4 Z and 0 6 Z ) were found to improve the DOF. Certain combinations of 0 4 Z and 0 6 Z provide a more effective method to expand DOF than using 0 4 Z or 0 6 Z alone, and this could be useful in the optimal design of presbyopic optical corrections such as multifocal contact lenses, intraocular lenses and laser corneal surgeries.

Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.

Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
Full Text

The reduction in visual performance typically found in keratoconic patients is believed to be associated with large magnitudes of uncorrected irregular astigmatism and higher-order aberrations (HOAs). Previous studies indicate that correcting HOAs in keratoconus patients may result in an improvement in visual performance. This thesis explores the correction of HOAs using standard sphero-cylindrical and customised aberration-controlling soft contact lenses in 22 patients with keratoconus. The findings of this work may be useful from a clinical perspective, as some keratoconic patients cannot tolerate rigid gas-permeable (RGP) contact lenses and have few alternatives, excluding surgical intervention, for vision correction. This thesis firstly describes a series of preliminary studies conducted to improve our current understanding of the HOAs manifested in keratoconus. The results of these investigations suggested that alterations in aberrations, due to changes in accommodation or variations in the pre-corneal tear film post-blink, were unlikely to hinder the correction of HOAs for keratoconic patients. Equally, it was ascertained that subjective refraction data provided significantly better visual acuity compared to objective, aberrometry-derived refractions for patients with keratoconus. The findings also show that both lower-order aberrations (LOAs) and HOAs displayed a larger degree of variability in keratoconic eyes compared to those previously reported for visually-normal subjects. Furthermore, significant increases in 3rd-order coma root mean square aberrations were found after temporarily suspending RGP contact lens wear for 16 keratoconic patients. The results of two clinical studies suggested that standard sphero-cylindrical soft lenses can, to some extent, mask HOAs in keratoconic patients; however, the visual performances achieved were found to be poorer compared to RGP lenses. Equally, the results showed that RGP lenses provide superior visual performances compared to customised, aberration-controlling lenses, in spite of the customised lenses providing comparable reductions in uncorrected HOAs. The inducement of superfluous HOAs and LOAs, through customised contact lens translations and rotations, were modelled using MatLab (version 7.6.0.324; The Mathworks, Natick, MA, US). The results confirmed that minimising the decentration of aberration-controlling contact lenses, to less than 5 degrees of rotation and less than 0.50 mm of translation, will help to achieve an optimal correction of HOAs. However, more stringent criteria were required for LOAs, where rotational displacements should be reduced to less than 3 degrees and translational displacements should be limited to less than 0.10 mm. In conclusion, the correction of HOAs for patients with keratoconus is possible using customised, aberration-controlling soft contact lenses; however, several factors will govern their success, including the repeatability and accuracy of HOA measurements for these irregular corneas, and the stability of the customised lenses on-eye.

Since adaptive optics was first used to correct the monochromatic aberrations of the eye over a decade ago there has been considerable interest in correcting the ocular aberrations beyond defocus and astigmatism. In order to understand the prospective benefits of correcting these higher-order aberrations it is important to study their effect on visual performance. From a clinical perspective it is important to know how different types of aberration can affect visual performance so that wavefront measurements can be better understood. Visual performance is determined by a combination of optical and neural factors. It is important to consider how degradations in the optical quality of the eye can impact the neural processes involved in visual tasks such as object recognition. In this thesis we present a study of the effects of three types of aberration, defocus, coma and secondary astigmatism, on letter recognition and reading performance. In the course of this work we also characterise the repeatability of the Zywave aberrometer, which we used to measure our subjects' ocular wavefronts. We use stimuli that have these aberrations applied in their rendering to examine the differences between these aberrations and how they differ with respect to the visual task. We find that secondary astigmatism causes the largest impairment to both letter recognition and reading performance, followed by defocus. Coma causes comparatively smaller degradations to performance but its effect is different depending on the visual task. We can predict the reduction in performance based on a simple cross-correlation model of letter confusability. The relationship between these predictions and the experimental results are the same for all three aberrations, in the case of single letter recognition. In reading however, the relationship is different for coma. We suggest that coma causes lateral masking effects and may additionally disrupt the planning of eye movements. Coma slows reading, but does not specifically impair word identification whereas defocus and secondary astigmatism do. We attribute disruptions in word identification to the dramatic effects defocus and secondary astigmatism have on the form of a letter.

This thesis describes a set of experiments investigating the impact of the higher-order aberrations of the eye on contrast sensitivity. The principal aim is to investigate if asymmetric blur induced by the aberrations of the eye can produce orientation selective effects. Orientation in contrast sensitivity testing has been largely ignored as it has been thought that the oblique effect, the preference for vertical and horizontal stimuli over obliques, was entirely neural in origin. Studies measuring the oblique effect were conducted using diffraction-limited pupils yet in larger pupils the higher order aberrations have an increasing impact on visual performance. These aberrations can be circularly asymmetric and so this raises the possibility that they may influence orientation selectivity when the pupil is large. The second aim of the study is to investigate orientation selective contrast sensitivity in refractive surgery patients.

Background Down's syndrome CDS) is the most common cause of learning disability in humans. Studies have described deficits in visual performance in DS that cannot be explained by ocular pathology, refractive errors, attentional or behavioural factors. Structural differences in the optics of the DS eye have been reported. It has also been previously reported that visual performance in DS is significantly improved when the optics of the eye are by-passed, suggesting an underlying optical defect. This thesis investigates whether optical quality is reduced in children with DS and how an optical deficit might influence their visual function. Methods Forty-four children with DS and 211 age-matched typically developing children participated in the main study. Optical quality was quantified by the measurement of higher order aberrations. Ocular structure and shape were also assessed to explore their influence on higher order aberrations and optical quality. Higher order aberrations were compared with visual performance measures of high and low contrast recognition acuity, grating resolution acuity and accommodative function. Higher order aberrations were also analysed for a large group of typically developing white Northern Irish children to explore the influences of age and refractive error on these measurements. Results & Conclusions The data demonstrated that: • Children with DS have greater levels of higher order aberrations and poorer optical quality than typically developing children. These differences were not attributable to greater levels of ametropia or premature aging in DS. • The data suggest multiple limitations of visual function in children with DS including optical and neural factors. • Neural adaptation and compensation of retinal image blur may be lacking or less efficient in DS resulting in poorer visual performance. • Negative spherical aberration found in the children with DS may indicate that differences in crystalline lens shape may restrict accommodative ability.

The outcome of higher order aberrations (HOAs) prior to, and following, age-related cataract extraction and intra-ocular lens (IOL) implantation was explored using placido disc skiaoscopy aberrometry. Ninety-nine individuals (median age 73.0, IQR 67.0, 80.5) underwent comprehensive ophthalmic examination including contrast sensitivity, endothelial cell imaging and aberrometry (Nidek OPD ARK-10000) at approximately 4 weeks pre-operatively (median 3.9, IQR 2.9, 4.8) 10 weeks (median 7.1, IQR 5.64, 11.71) (67 individuals) and 80 weeks (median 85.1, IQR 80.0, 89.6) (41 individuals) post-operatively. Linear relationships between thirteen demographical, functional and structural variables and each of three components, Total (TC), Corneal (CC) and Internal (IC), for each of eight HOAs, were separately explored, using Analysis of Variance, for each examination and for the pre- and post-operative differences, respectively. The TC and IC of all HOAs decreased post-operatively (p≤68%). Preoperatively, the TC and IC of the Total HOA decreased as the spherical equivalent (SE) became less negative (both p<0.001, R2=0.56 and 0.53). Both components of the Total HOA also decreased as the difference in SE between baseline and each follow-up became less negative (all p≤0.008, R2=0.45-0.61); the magnitude of the reduction varied between IOL type (p≤0.008). The IC of the Tilt, T.Sph and HiAstig HOAs increased with increase in severity of posterior subcapsular (p=0.018), of cortical (p=0.013) and of combined nuclear colour and cortical cataract (p=0.003), respectively. The relationship between cataract type and severity and reduction in post-operative HOA was not statistically significant at either follow-up examination. Slight associations, presumably due to post-operative corneal oedema, were present between increase in CCs of five HOAs and decreasing endothelial cell density at the first follow-up, only, (all p≤0.030, R2=0.09-0.14). Pre-operative TCs and ICs were larger, respectively, than those of 22 individuals with ‘less severe’ cataract and post-operatively than those of 49 individuals with clear media, obtained from retrospective data.

Derivation of analytical refraction, propagation and reflection equations for Higher Order Aberrations of wavefronts From literature the analytical calculation of Lower Order Aberrations (LOA) of a wavefront after refraction, propagation and reflection is well-known, it is for local Power and Astigmatism performed by the Coddington equation for refraction and reflection and the classical vertex correction formula for propagation. However, equivalent analytical equations for Higher Order aberrations (HOA) do not exist. Since HOA play an increasingly important role in many fields of optics, e.g. ophthalmic optics, it is the purpose of this study to extend the analytical Generalized Coddington Equation and the analytical Transfer Equation, which deals with second order aberration, to the case of HOA (e.g. Coma and Spherical Aberration). This is achieved by local power series expansions. The purpose of this PhD was to extend the analytical Generalized Coddington Equation and the analytical Transfer Equation, which deals with Lower Order Aberrations (power and astigmatism), to the case of Higher Order Aberrations (e.g. Coma and Spherical Aberration). In summary, with the novel results presented here, it is now possible to calculate analytically the aberrations of an outgoing wavefront directly from the aberrations of the incoming wavefront and the refractive or reflective surface and the aberrations of a propagated wavefront directly from the aberrations of the original wavefront containing both low-order and high-order aberrations.

For more than a century it has been known that the eye is not a perfect optical system, but rather a system that suffers from aberrations beyond conventional prescriptive descriptions of defocus and astigmatism. Whereas traditional refraction attempts to describe the error of the eye with only two parameters, namely sphere and cylinder, measurements of wavefront aberrations depict the optical error with many more parameters. What remains questionable is the impact these additional parameters have on visual function. Some authors have argued that higher-order aberrations have a considerable effect on visual function and in certain cases this effect is significant enough to induce amblyopia. This has been referred to as ‘higher-order aberration-associated amblyopia’. In such cases, correction of higher-order aberrations would not restore visual function. Others have reported that patients with binocular asymmetric aberrations display an associated unilateral decrease in visual acuity and, if the decline in acuity results from the aberrations alone, such subjects may have been erroneously diagnosed as amblyopes. In these cases, correction of higher-order aberrations would restore visual function. This refractive entity has been termed ‘aberropia’. In order to investigate these hypotheses, the distribution of higher-order aberrations in strabismic, anisometropic and idiopathic amblyopes, and in a group of visual normals, was analysed both before and after wavefront-guided laser refractive correction. The results show: (i) there is no significant asymmetry in higher-order aberrations between amblyopic and fixing eyes prior to laser refractive treatment; (ii) the mean magnitude of higher-order aberrations is similar within the amblyopic and visually normal populations; (iii) a significant improvement in visual acuity can be realised for adult amblyopic patients utilising wavefront-guided laser refractive surgery and a modest increase in contrast sensitivity was observed for the amblyopic eye of anisometropes following treatment (iv) an overall trend towards increased higher-order aberrations following wavefront-guided laser refractive treatment was observed for both visually normal and amblyopic eyes. In conclusion, while the data do not provide any direct evidence for the concepts of either ‘aberropia’ or ‘higher-order aberration-associated amblyopia’, it is clear that gains in visual acuity and contrast sensitivity may be realised following laser refractive treatment of the amblyopic adult eye. Possible mechanisms by which these gains are realised are discussed.

Myopia (short-sightedness) arises in childhood due to excessive eye growth and is linked with near work activities. However the underlying mechanisms remain unclear. This thesis examined the short-term optical and structural changes in the eyes of children while focusing at close reading distances and identified important differences between myopic and non-myopic children. The prevalence of myopia is increasing globally, particularly in South-East Asia, and these findings provide new insights into potential mechanisms linking near work and the development and progression of myopia during childhood.

The 2010 National Education Technology Plan steadily replaces paper textbooks with study materials on computers. One risk of increased computer usage is increased Computer Vision Syndrome (CVS) symptoms. I researched multiple studies to analyze the effects of computer use on dry eye and eye strain and how these symptoms can progress to musculoskeletal pain, headaches, decreased quality of life, loss of confidence and even anxiety and depression. Currently, there is not much data on tablet use so I propose two future experiments to determine if tablets can also cause CVS ocular symptoms.

Blur adaptation is the improvement of visual and perceptual performance with time following viewing of a blurred target. It is possible to generate blurred images with two different methods – source and observer methods. This study compared blur adaption with source and observer methods for combinations of defocus and higher-order aberrations. Participants adapted to a blurred natural scene for 1 minute and performed a visual acuity task with tumbling Es. Negligible blur adaption was noticed for both source and observer methods. A longer adapting period might be necessary to achieve significant improvement in visual acuity following blur adaptation.

Retinal photoreceptor directionality of human eye refers to the fact that, for a normal and healthy human eye, visual sensitivity is greatest for light entering near the centre of the eye pupil and the response falls off from this peak roughly symmetrically across the pupil. This is also known as the Stiles-Crawford effect (SCE). It is achieved by the directionality of retinal cones that act like waveguides. It has a positive effect on human vision since the optical aberrations of the eye normally increase in the pupil periphery. The measured SCE is used in clinical cases to indicate the stage and degree of various retinal abnormalities. Directionality of human cones is traditionally measured either by psychophysical or reflectometric methods; several other methods have also been proposed for measuring and modelling the cone directionality. Cone directionality and aberrations of the eye are widely varied from subject to subject. It has been suggested that they are actively controlled and there may also exist a natural relationship between the directionality and aberrations. But the current methods to accurately measure the cone directionality are difficult and time consuming. In this research, we developed a mathematical model of the cone directionality based on the measured monochromatic aberrations of the human eye. We show that cone directionality can be modelled using a two-dimensional Gaussian function whose parameters vary according to the measured monochromatic aberrations of the eye. Our modelling is based on a hypothesis that cones directionality is optimised so that the resulting retinal image quality is maximised. This methodology can also be used in automatic image enhancement systems for correcting higher-order aberrations. The modelling of the SCE of the human eye as a Gaussian function has been demonstrated. The optimisation process that we developed has been used to optimise ten different eyes, which all have significant amount of higher order aberrations. It has shown significant improvement in the corresponding Point Spread Functions. The proposed methodology could be used for cost-effective image enhancement in optical systems, which suffer from higher-order monochromatic aberrations. Currently such systems have to be corrected with adaptive optics.

碩士
國立臺灣大學
臨床醫學研究所
94
Laser refractive surgery is performed by using Ar-F excimer laser to disrupt the inter-molecular bonding of corneal tissue and ablate the cornea, thereby changing the curvature and refractive power of anterior corneal surface. However, as soon as the spherical and cylindrical refractive errors are corrected by laser, higher-order aberrations of anterior corneal surface also result. This is due to the irregular change of anterior corneal surface by wound healing process or the laser treatment itself. The surgical and mechanical techniques of laser refractive surgery have been processing during the past decade. Photorefractive keratectomy (PRK) was preformed in the past, whereas laser in situ keratomileusis (LASIK) is used most often at present time. The laser beams also evolve from broad beams to flying spots and mixed spots. Since the laser refractive surgery itself induces the higher order aberrations of anterior corneal surface, these different surgical techniques and machines attribute differently to the higher-order aberration (HOA). In this study, we calculate the HOAs of anterior corneal surface by computerized corneal topography and calculating software. We then analyze the affecting factors of HOA changes after surgery, including surgical techniques (PRK vs. LASIK), laser machines (Summit Apex Plus, Allegretto Wave, Bausch & Lomb Technolas 217z, and VISX S4), age, attempted sphere correction, attempted cylinder correction, optic zone size, and transitional zone size. Besides, we use questionnaires to evaluate the visual quality and the extent of satisfaction of patients, and analyze the relationships with corneal surface HOA changes. As the result shows, all HOAs increased significantly after surgery by various techniques and machines. LASIK induced more trivial HOAs (the 5th and 6th orders) after surgery than PRK did. The diopters of spherical equivalent corrected were highly correlated with surgical-induced HOA changes. Patients with older ages had less HOA changes. The larger the treatment zone sizes (including optic zones and transitional zones), the less the surgical-induced HOA changes. Some flying-spot machines induced less coma-like aberrations, while no obvious differences of spherical-like aberrations and total HOAs between broad-beam machines and flying-spot ones were noted. The visual quality and the extent of satisfaction of patients correlated most strongly with spherical-like aberrations, then with total HOAs, and then with coma-like aberrations. In the future, we can try to improve the surgical techniques and the preciseness of laser machines according to these results. We hope our efforts can contribute to more perfect visions of future patients!

No
We measured the wavefront aberrations of the eyes of five subjects with a Shack-Hartmann sensor sampling at 21.2 Hz and decomposed the measurements into Zernike aberration terms up to and including the fifth radial order. Coherence function analysis was used to determine the common frequency components between the aberrations within subjects. We found the results to be highly subject dependent. The coherence values were typically <0.4. Possible reasons for this are discussed. Coherence function analysis is a useful tool that can be used in future investigations to determine correlations between the aberration dynamics of the eye and other physiological mechanisms.

碩士
臺灣大學
臨床醫學研究所
95
With the advances in surgical instruments, IOL design and material, IOL delivery system and surgical technique, the small cornea incision cataract surgery with implantation of IOL have become a successful procedure that provides fast visual rehabilitation and minimum surgical complications. However, improvement of postoperative visual acuity is not the only concern today but also the visual quality and functional vision. Therefore, eliminating optical aberrations,especially high-order aberrations（HOAs）is one way to achieve the goal. The optical aberrations are mainly from two parts of the eye, cornea and lens. Both corneal and lenticular HOAs increase during the aging process, therefore affect the functional vision. Though the opacified lens is replaced by a crystal clear optics during the cataract surgery, the disturbance of the compensatory effect of nature lens to positive corneal spherical aberration has been made by the conventional spherical intraocular lens. Therefore a new IOL design with aspherical anterior surface was developed during recent years, which generate negative spherical aberrations to compensate for corneal aberration, in order to improve functional visions for cataract patients. In this study, we use corneal topography and wavefront aberrometer to analyze corneal and total ocular high-order aberrations. In addition, we use contrast sensitivity and contrast acuity as indicators of visual function and try to investigate: 1) the impact of aging on corneal and total ocular HOAs 2) the change of HOAs after the cataract surgery 3) to compare intraindividually the HOAs and functional vision between implantation of spherical and aspherical IOLs. The results reveal that: Corneal HOAs, including total 3rd, total 4th, total 5th order, coma and primary spherical aberrations, have minimal changes with increase of age. After the small incision clear cornea cataract surgery with , the corneal HOAs increase minimally, but the total ocular HOAs increase significantly compare to normal phakic eyes, especially the total 4th –order and primary spherical aberrations. Compare to conventional spherical IOLs, implantation of aspherical IOLs indeed reduce the ocular spherical aberrations. As for the functional vision, we don’t see significant improvement of aspherical IOLs over conventional spherical IOLs. We speculated that patients with smaller pupil size may not gain the visual benefit provided by the aspherical IOLs. Aberrations affect vision differently, further investigation for customized IOLs, with ranges of aberrations corrected to suit individual needs, may be needed.

碩士
高雄醫學大學
醫學研究所
97
2. Abstract 2.1. Purpose: To investigate the influence of myopia, refractive factors and age on corneal or ocular aberrations and the changes in contrast sensitivity. 2.2. Methods: A total of 82 eyes of 52 subjects were evaluated, using Wavelight Topolyzer and Wavelight Analyzer.Other measurements included age, contrast sensitivity functions, intraocular pressure, keratometry readings, axial length, basic secretion tests, central cornea thickness, manifest and cycloplegic refraction. We analyzed the association of higher-order aberrations between cornea and globe, and the differences among other ocular parameters. 2.3. Results: The data showed that ocular aberration C8 (r=0.272，p<0.05) and C18 (r=0.300，p<0.01) increased with tear volume. Ocular aberration C11 increased with axial length (r=-0.297，p<0.01). Both corneal (r=0.574，p<0.05) and ocular (r=0.919，p<0.01) C7 showed positive correlations with corneal thickness in participants aged older than 40. Ocular C17 (r=0.257，p<0.05)increased with higher vertical keratometry values, and horizontal keratometry values was associated with total-higher order aberrations (RMSh)(r=0.267，p<0.05). Myopia diopter affects ocular C7 (r=0.262，p<0.05) which influences contrast sensitivity function at 18 cpd (r=-0.245，p<0.05).Ocular C8 increased with age (r=0.106，p<0.01), but had no association with contrast sensitivity. 2.4. Conclusion: Corneal and ocular aberrations are different for many ocular factors such as refractive errors, axial length, corneal thickness, keratometry, tear volume and age.Ocular aberration C8 and C18 increased with tear volume. Ocular aberration C11 showed positive correlation with axial length.Both corneal and ocular aberration C7 showed positive correlations with corneal thickness.Higher vertical corneal k-value was associated with ocular aberration C17,and higher horizontal corneal k-value was associated with total higher- order ocular aberrations (RMSh). Higher myopia was associated with increasing ocular aberration C7 and reduced contrast sensitivity in 18 cpd.Older age was associated with higher ocular aberration C8, but C8 did not interfere with contrast sensitivity at any spatial frequency indepdently.

Wavefront-guided (WFG) laser in situ keratomileusis (LASIK) differs from conventional surgery by applying a refined algorithm for tissue removal, based on information from preoperative wavefront aberration data. Since the introduction of this technology, there have been few investigations comprehensively reporting outcomes, particularly for hyperopic treatments. This thesis aimed to determine the impact of myopic and hyperopic WFG LASIK on visual acuity, contrast sensitivity, higher order aberrations and subjective ratings, as well as determine the relationship between these outcome measures. Bilateral WFG LASIK was performed on 324 myopic eyes (162 subjects) and 62 hyperopic eyes (31 subjects). High contrast (HC) and low contrast (LC) best-corrected visual acuity (BCVA) and contrast sensitivity were assessed using ETDRS charts and vertical sinusoidal gratings, respectively. Higher order ocular aberrations were measured using a Shack-Hartmann wavefront sensor and analyzed across a 5.0 mm pupil. Subjective ratings were assessed using a closed-ended categorical questionnaire. Assessments were conducted prior to surgery and at three and six months postoperatively. WFG LASIK had minimal impact on BCVA and contrast sensitivity; however there was an impact on the magnitude and profile of higher order aberrations, which differed between the myopic and hyperopic groups. There was a greater increase in higher order aberrations for the hyperopic group, who also had a tendency to have lower visual outcomes and worse subjective ratings. Despite these results, there were no associations between subjective ratings and higher order aberrations, LC BCVA or contrast sensitivity for both groups and a clear understanding of the relationship between these outcome measures was not apparent. Factor analysis revealed a variety of factors that contributed to the outcome measures for this data set, with the three main factors being: subjective ratings, vision and optical quality. In conclusion, WFG LASIK had excellent outcomes in terms of visual acuity, contrast sensitivity, and subjective ratings, despite an increase in higher order aberrations compared with those found prior to surgery. Hyperopic outcomes were slightly worse than myopic outcomes. Further investigation is required to determine the impact of higher order aberrations on visual acuity, contrast sensitivity and subjective ratings, as well as the relationship between these measures.

碩士
中臺科技大學
醫學工程暨材料研究所
104
Purpose: In order to analysis the photography from the space accurately, NASA has invented a new technology called wavefront. Because the new technology has been used on Optometry widely recent year, different wavefront aberrometers have been designed and applied on clinic. Although the visual acuity improves after LASIK, visual quality becomes worse because of the increase of wavefront aberration. Visual quality is multifactorial which is not only decided by the prescription of diopter but also many other factors so that we should pay more attention to the study of the application of wavefront aberration and know all of aberrations of human eyes correctly which can help the clinical application. Here, we study different aberrometers on correlation between the high-order aberrations and the low-oder aberrations. Methods: In total,32 adults (64 eyes) including 15 females and 17 males whose average age is 31.41±3.82(from 24 to 38), average spherical diopter is -3.92±3.01D and average astigmatism is -1.07±0.98D by using NIDEK OPD SCAN III and HUVITZ 8000A aberraometor and each system was measured three times. Then we analyzed data by paired-samples T, correlation analysis and repeat measure (Bonferroni correction). Results: There is no difference between HUVITZ aberrometor and subjective refraction in low-order aberrations by using paired-samples T, but it has a significant difference from HUVITZ 8000A. According to the statistical analysis about high-order, there is just a postive correlation between NIDEK OPD SCAN III and HUVITZ 8000A aberraomteor in tile clover aberration and verical coma aberration, and has negative correlation between spherical aberration and horizontal clover, and no difference in horizontal coma aberration. Conclusion: There is high correlation between NEDIK OPD SCAN III and HUVITZ 8000A aberraometor when testing the high-order aberrations. However we must pay more attention to the difference about the astigmatism axial and diopter testing by aberraometor and overrefraction. Although NEDIK OPD SCAN III and HUVITZ 8000A aberraometor are lastest phoropter, they still need a large number of clinical sample so that they will have high reliability on testing high-order aberration. Key word: wavefront, high-order aberration, NEDIK OPD SCAN III, HUVITZ 8000A

碩士
中山醫學大學
生物醫學科學學系碩士班
102
Laser in situ keratomileusis (LASIK) is one of the common ways to improve myopia. Producing a high quality corneal flap is the key to a successful LASIK, where complications usually take place thus affecting the visual quality. Different instruments and methods used would create different corneal flaps. In the past corneal flaps were produced using Mechanical Microleratome, but Femtosecond Laser has slowly took over Mechanical Microleratome recently. Therefore, this study was to evaluate the visual quality and dry eye after LASIK surgery by the means of IntraLase FS60 femtosecond laser, Technolas 520F femtosecond laser, Ziemer FEMTO LDV femtosecond laser and Microkeratome to create corneal flap. This retrospective study, seventy eyes of 36 patients underwent LASIK where IntraLase FS60 femtosecond laser were performed on twenty-three eyes of 11 patients, Technolas 520F femtosecond laser were performed on nineteen eyes of 10 patients, Ziemer FEMTO LDV femtosecond laser were performed on sixteen eyes of 9 patients, and Microkeratome were performed on twelve eyes of 6 patients. All eyes were examined with wavefront analysis and with the use of VISX STAR S4 Excimer Laser System (VISX Inc., Santa Clara, USA) to carry out the excimer laser ablation. All patients had undergone clinical examination 6 months prior to the surgery and 6 months after the surgery which includes Visual Acuity, Spherical refraction, Astigmatism, Spherical Equivalent (SE), Contrast Sensitivity, High Order Aberrations (HOAs), tear secretion and corneal sensation. The results show there were no significant difference between Uncorrected Distance Visual Acuity (UDVA), Corrected Distance Visual Acuity (CDVA), Spherical refraction, Astigmatism, SE, and Schirmer’s tear secretion 6 months after the surgery (all P > 0.05). Contrast sensitivity part, only 6 cpd in mesopic that Femtec group were significantly lower than others (P< 0.05). For the all HOAs, Femtec group were significantly higher than the Ziemer group (P < 0.05) ; for the Coma aberration, Femtec group were also higher than the IntraLase group, Ziemer group, MK group (all P < 0.05); for Spherical aberration, Ziemer group were higher than IntraLase group and MK group (all P < 0.05); for RMS3, Femtec group are higher than IntraLase group, Ziemer group, MK group (all P < 0.05) ; as for Trefoil aberration there are no significant difference between the RMS4, RMS5 and RMS6 group (all P > 0.05 ). For corneal sensation, Femtec group were significantly lower than others. (all P < 0.05). According to the results that there are no significant difference in the visual acuity and refractive errors with the use of different instruments to create corneal flap 6 months after surgery. However, there is a significant worse in the HOA with the use of Technolas 520F femtosecond laser to create corneal flap compare to the other instruments.

碩士
中山醫學大學
生物醫學科學學系碩士班
103
Background and Purpose: Apart from manifest refractive error, the quality of vision is affected by various factors. With the capability of analyzing most of the aberration in the eye, wavefront sensor has been widely used in many aspects of ophthalmic application. However, there were few analytical studies done regarding high-order aberration and its influencing factors. The purpose of this study is to analyze the distribution of ocular high-order aberration and to investigate its relationship with various physiological properties in Taiwanese adults. This retrospective study will help to better understand the effect of high-order aberration on human visual quality. Material and Method: This retrospective study data was obtained from 312 patients who underwent a comprehensive ocular-visual evaluation as a routine procedure prior to refractive laser surgery from the year 2008 to 2012. The age of the population ranged from 20 to 56.The spherical component of their manifest refraction ranged from -1.50D through -10.50 D. The cylinder component of the manifest refraction was less than -3.50 D.To obtain research data included basic information, auto- refractor measurement (TOPCON Auto Kerato-Refractometer KR-8900), subjective refraction, pupil size (in daylight and darkroom), Wavefront scan: AMO WaveScan WaveFront™ System (wavescan mode),corneal thickness, and tear test result.Data analysis: Statistical analysis was conducted using Statistical Package for Social Science (SPSS, PASW Statistics 18 SPSS18).Repeated-measures one way analysis of variance (One way ANOVA) was performed to examine the statistical significance of variations in aberrations between various groups. We were also used Independent-Samples t Test, Partial Correlation, and linear regression to compare groups and post hoc to check the correlation.Results:Our results showed the scotopic pupil size is significantly correlated with spherical aberration (r=0.154, F=0.007),coma (r=0.201, F=0.000), and trefoil (r=0.240, F=0.000). Spherical aberration and spherical equivalent are significantly correlated.(r=0.219, P=0.001).Spherical aberration increases with age, and they are positively correlated(r=0.193, F=0.002).Coma and astigmatism are significantly positively correlated(r=0.278, F=0.000).Trefoil and astigmatism are significantly correlated(r=-0.138, F=0.020). The spherical aberrations are different between genders. Spherical aberration is found to be higher in patients wearing RGP vs. Soft contact lens previously. Conclusion:Based on our result, the scotopic pupil size is significantly correlated to coma, trefoil and spherical aberration; therefore it has a great impact on the total higher-order aberration. Significant positive correlation was also found between spherical aberration and age, this suggests the compensation mechanism of spherical aberration between cornea and crystalline lens reduces with age. Although statistically we found many ocular physiological factors to be significantly correlated with higher-order aberrations, more research is needed to confirm the relationship. This project allows us to analyze the distribution of higher-order aberrations among Taiwanese adults and hopefully to identify its influencing factors and the effect on visual quality.

碩士
國防醫學院
航太醫學研究所
95
Introduction: It has long been appreciated that vision is limited by both optical and neural factors, but that only optical factors can be easily and effectively corrected for. Chief among these optical factors are spherical refractive error and astigmatism. Recent advances in wavefront technique make it possible to reduce postoperative order aberrations (HOAs) via modern refractive surgery such as wavefront guided laser in situ keratomileusis (WG LASIK). The goal of this research is to clarify an important question that has implications for both clinical and applied vision in aviation. “How important is iris registration and femtosecond laser (Intralase) technology in postoperative HOAs after WG LASIK?” Purpose: (1) To quantify the cyclotorsion occurring between upright sitting (measurement) position and supine (surgical) position in Taiwanese. (2) To compare the HOAs change after WG LASIK with iris registration (IR) and without iris registration (NIR) system. (3) To compare HOAs change after WG LASIK using a corneal flap with Moria microkenatome (M2) group and Intralase group based on the Hartmann-Shack wavefront aberrometer. Methods: (1) To determine the amount of cyclotorsion of eyeball between the measurement and surgery in 105 eyes (54 patients). (2) Twenty-eight eyes from 14 patients (refraction range -2.50D~-7.50D) treated by W G LASIK with IR group (12 eyes) or NIR group (16 eyes). Root-mean-square (RMS) of coma-like aberration, spherical aberration, total 3rd to 6th order HOAs were compared between the two groups. (3) M2 group (18 eyes) and Intralase group (12 eyes) whose degrees of myopia were-1.00 to –8.00 diopters (D) were treated with W G LASIK. Root-mean-square (RMS) of coma-like aberration, spherical aberration, total 3rd to 6th order HOAs were compared between the two groups. Result: (1) For all 105 eyes, mean ± standard deviation (SD) cyclotorsional deviation was 2.6 ± 2.0 degrees (right eye 2.4 ± 3.8 degrees counterclockwise, left eye 2.7 ± 2.9 degrees clockwise). (2)Compared with preoperative aberrations, both IR and NIR group showed postoperative decreased of total aberration (p<0.01) and increased of HOAs, vertical coma, and spherical aberration (p<0.01). Compared with NIR group, significant reduction of HOAs, vertical coma, and spherical aberration was observed in IR group. (3) There were no significant differences in RMS of coma-like aberration, spherical aberration, total 3rd to 6th order HOAs between M2 and Intralase group. Conclusions: (1) The difference of cyclotorsional eye movement was assessed significantly in the transition from seated to supine position with IR technology. (2) The WG LASIK with IR system significantly decreased postoperative induction of the amount of HOAs, vertical coma, and spherical aberration. (3) Although postoperative visual acuity improved significantly in Intralase group, there was no significant difference in all items of HOAs between the M2 group and Intralase group. Further study of multiple variants affecting postoperative HOAs after Intralase flap creation is mandatory. In summary, our study demonstrated that using IR system is essential element for reduction of postoperative HOAs after WG LASIK.