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The main purpose of this thesis is to create and validate a visual acuity model with experimentally obtained aberrations of human eyes. The other motivation is to come up with a methodology to objectively predict the potential benefits of photorefractive procedures such as customized corrections and presbyopic LASIK treatments. A computational model of visual performance was implemented in MATLAB based on a template matching technique. Normalized correlation was used as a pattern matching algorithm. This simulation describes an ideal observer limited by optics, neural filtering, and neural noise. Experimental data in this analysis were the eye’s visual acuity (VA) and 15 modes of Zernike aberration coefficients obtained from 3 to 6 year old children (N=20; mean age= 4.2; best corrected VA= 0 (in log MAR units)) using the Welch Allyn Suresight instrument. The model inputs were Sloan Letters and the output was VA. The images of Sloan letters were created at LogMAR values from -0.6 to 0.7 in steps of 0.05. Ten different alphabet images, each in ten sizes, were examined in this model. For each simulated observer the results at six noise levels (white Gaussian noise) and three levels of threshold (probability of the correct answer for the visual acuity) were analyzed to estimate the minimum RMS error between the visual acuity of model results and experimental result.

The main purpose of this thesis is to create and validate a visual acuity model with experimentally obtained aberrations of human eyes. The other motivation is to come up with a methodology to objectively predict the potential benefits of photorefractive procedures such as customized corrections and presbyopic LASIK treatments. A computational model of visual performance was implemented in MATLAB based on a template matching technique. Normalized correlation was used as a pattern matching algorithm. This simulation describes an ideal observer limited by optics, neural filtering, and neural noise. Experimental data in this analysis were the eye’s visual acuity (VA) and 15 modes of Zernike aberration coefficients obtained from 3 to 6 year old children (N=20; mean age= 4.2; best corrected VA= 0 (in log MAR units)) using the Welch Allyn Suresight instrument. The model inputs were Sloan Letters and the output was VA. The images of Sloan letters were created at LogMAR values from -0.6 to 0.7 in steps of 0.05. Ten different alphabet images, each in ten sizes, were examined in this model. For each simulated observer the results at six noise levels (white Gaussian noise) and three levels of threshold (probability of the correct answer for the visual acuity) were analyzed to estimate the minimum RMS error between the visual acuity of model results and experimental result.

Diss.--Biologie moléculaire--Göteborg--Göteborg university, 2002. / Bibliogr. p. 40-47.

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

Developments in nanotechnology and material science have produced optical materials with astonishing properties. Theory and experimentation have demonstrated that, among other properties, the law of refraction is reversed at an interface between a naturally occurring material and these so-called metamaterials. As the technology advances metamaterials have the potential to vastly impact the field of optical science.In this study we provide a foundation for future work in the area of geometric optics and lens design with metamaterials. The concept of negative refraction is extended to derive a comprehensive set of first-order imaging principles as well as an exhaustive aberration theory to 4th order. Results demonstrate congruence with the classical theory; however, negative refraction introduces a host of novel properties. In terms of aberration theory, metamaterials present the lens designer with increased flexibility. A singlet can be bent to produce either positive or negative spherical aberration (regardless of its focal length), its contribution to coma can become independent of its conjugate factor, and its field curvature takes on the opposite sign of its focal power. This is shown to be advantageous in some designs such as a finite conjugate relay lens; however, in a wider field of view landscape lens we demonstrate a metamaterial's aberration properties may be detrimental.This study presents the first comprehensive investigation of metamaterial lenses using industry standard lens design software. A formal design study evaluates the performance of doublet and triplet lenses operating at F/5 with a 100 mm focal length, a 20° half field of view, and specific geometric constraints. Computer aided optimization and performance evaluation provide experimental controls to remove designer-induced bias from the results. Positive-index lenses provide benchmarks for comparison to metamaterial systems subjected to identical design constraints. We find that idiosyncrasies in a metamaterial lens' aberration content can be exploited to produce imaging systems that are superior to their conventional counterparts. However, in some circumstances the reduced low-order aberration content in a metamaterial lens reduces the effectiveness of aberration balancing and stop shifting. Through a series of design experiments the relative advantages and challenges of using metamaterials in lens design are revealed.

The primary distinction between an ordinary optical system and one which is both unobscured and reflective is that the elements of the latter must be tilted or decentered with respect to one another. In general, this results in an optical system which has no axis of rotational symmetry, and therefore the classical aberration theory of symmetric systems is no longer applicable. Furthermore, the image becomes anamorphic and keystone distorted, due to the relative tilt between the object and the optical surfaces. The first part of this work is the development of a semi-analytic treatment of the properties (through third order) of systems possessing large tilts and decentrations. The Gaussian properties of both the image and pupil are described in terms of tilt, decentration, magnification, keystone distortion, and anamorphic distortion parameters. In computing these parameters, it is important to take into account the transferred components of the parameters, which are due to the Gaussian properties of the preceding surfaces. The third order properties are computed using the fact that each optical surface, together with its associated entrance pupil, form an optical subsystem which possesses an axis of approximate symmetry. About this axis, the aberration contributions of that surface may be described in the classical wave aberration expansion. The coefficients in this expansion may be corrected for the non-circular appearance of both the object and pupil, using the parametric description of their Gaussian form. the aberration fields due to the various surface contributions are then combined vectorally to yield the resultant aberration field in the image plane. The vector theory is applied to the analysis of several optical systems, and the accuracy of the theory verified by comparison with raytrace data. As a demonstration of the usefulness of the theory to an optical designer, a three mirror unobscured system was designed using a methodology derived from the theory. At each step, the design options are explained, and the probable results are discussed. The residual aberrations of the resulting system are studied, and the selection of another design starting point is discussed from the point of view of the theory.

The impact of uncoordinated growth of the optical components of the eye may stimulate different levels of monochromatic aberrations in the growing eyes of the children. This thesis aimed to examine the impact of age, visual acuity and refractive error on higher order aberrations as well as to determine the relationship between them. Hartman Shack images taken with the Welch Allyn® SureSight Autorefractor were calibrated in order to determine the Zernike coefficients up to the 8th order for a pupil diameter of 5mm. The MATLAB code proposed by Thibos et al that follows the standard for reporting the optical aberrations of the eye was the basis of code written for this study. Modification was required to suit the specific needs of the Welch Allyn® SureSight Autorefractor. After calibration the lower order aberrations could then be compared with the results from cyclopledged retinoscopy. RMS values of aberrations and Strehl ratios were computed to examine the optical performance of the eye. A total of 834 Hartmann-Shack images of 436 children (mean age 3.94± 0.94 years, range 3 to 6 years) were examined in this study (right eyes 436; left eyes 398).The sample had a mean (± STD) spherical equivalent of 1.19 ± 0.59D, a mean with-the-rule astigmatism (J0) of 0.055 ± 0.22D, and a mean oblique astigmatism (J45) of 0.01±0.14D. Visual acuity varied from 6/6 to 6/18. Moderate mirror symmetry was found between the eyes. Like refractive error, higher order aberrations declined with age in this sample. There was an impact of higher order aberrations on refractive error. Significantly higher ocular aberrations were found in the higher hyperopic group (SE>+2.0D) compared to emmetropic (-0.5<SE<+0.5D) and low hyperopic groups (+0.5<SE<+2.0D). The Strehl ratio was significantly lower in the high hyperopic group. Higher Strehl ratios were observed for better acuity groups but the average Strehl ratios among the different visual acuity groups were not statistically significant. In conclusion, there was an impact of age on the ocular aberrations. A wider range of age from birth to adolescence is required for further investigation. This could be indirectly influenced by the age related changes in refractive error as the correlation between refractive error and the higher order aberrations were significant. This finding also concludes that Strehl Ratio alone is not capable of perfectly describing the visual acuity of the eye; other metrics such as the neural transfer function and neural noise are necessary to describe the resultant visual performance of the eye.