L'objectif de ces travaux était de tester la capacité d'une simulation numérique à prédire la vision subjective, dans différents conditions d'aberrations comparables aux optiques multifocales. Nous avons tout d'abord qualifié la vision subjective par la profondeur de champ, définie comme la zone de vision considérée comme acceptable par les sujets. Le calcul de critères de qualité d'image (i.e. simulation numérique) ne permettait pas de prédire la profondeur de champ (r² < 0.35). Le calcul d'images simulées, qui, contrairement aux critères de qualité d'image, demandait une réponse des sujets, a permis de démontrer que le modèle d'œil permettait de rendre compte de l'optique, mais pas de l'acceptabilité d'une cible par les sujets. Face au manque de finesse de la prédiction de ce critère de vision subjective, nous avons évalué la qualité de vision de façon continue : les sujets avaient pour tâche de noter des images sur une échelle de gradation. Les sujets notaient ainsi leur vision à différentes proximités et dans différentes conditions d'aberration. La prédiction de la vision subjective par ce critère était plus précise (r² = 0.92). Cependant, cette corrélation tendait à diminuer pour les qualités d'image très faibles. Il semblerait donc que la prédiction de la vision subjective passerait par l'utilisation de différents critères de qualité d'image, permettant de qualifier aussi bien une bonne qu'une mauvaise qualité de vision.

Thesis--University of Turku, 1984. / At head of title: From the Institute of Dentistry and the Institute of Biomedicine, University of Turku. Extra t.p. with thesis statement inserted. Also published in: Proceedings of the Finnish Dental Society, Vol. 80, 1984, Suppl. V. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 117-143).

In this dissertation fully general conditions are presented to correct linear and quadratic field dependent aberrations that do not use any symmetry. They accurately predict the change in imaging aberrations in the presence of lower order field dependent aberrations. The definitions of the image, object, and coordinate system are completely arbitrary. These conditions are derived using a differential operator on the scalar wavefront function. The relationships are verified using ray trace simulations of a number of systems with varying degrees of complexity. The math is shown to be extendable to provide full expansion of the scalar aberration function about field. These conditions are used to guide the design of imaging systems starting with only paraxial surface patches, then growing freeform surfaces that maintain the analytic conditions satisfied for each point in the pupil. Two methods are proposed for the design of axisymmetric and plane symmetric optical imaging systems. Design examples are presented as a proof of the concept.

No description available.

The cornea is the most powerful refractive component of the eye and as such, subtle changes in corneal shape can cause substantial changes in the optical characteristics of the eye. Monocular diplopia has previously been linked to corneal distortion following near work in various studies but has not been investigated in detail. The work reported in this thesis has investigated the optical effects of corneal distortions caused by eyelid forces and demonstrated that several corneal higher and lower order Zernike wavefront aberrations can change following reading. Measuring subtle changes in corneal topography requires the highest possible instrument accuracy, while software analysis tools should be able to detect and highlight those subtle changes with high reliability. The effect of ocular microfluctuations on the qualitative and quantitative analysis of corneal topography was investigated. A technique was developed to measure tilt, displacement, and cyclotorsion in multiple videokeratographs from the same cornea. This information was used to reposition each videokeratograph according to the average position of a sample of multiple measurements. The corneal topography of ten subjects was measured 20 times each, using videokeratoscopy. The RMSE calculated from difference between single videokeratographs and the average videokeratograph decreased by an average of 24.6 % for the ten subjects' data. The method can improve the precision performance of videokeratoscopy in multiple measurements of corneal topography. A study was undertaken, to investigate whether there are significant changes in corneal topography during accommodation in normal corneas and corneas that are pathologically thinner due to keratoconus. This was done to eliminate the possibility that changes in corneal aberrations associated with near work could be at least partly due to corneal changes caused by the effects of accommodation. A videokeratoscope was modified to present an accommodation stimulus that was coaxial with the instrument's measurement axis. Six subjects with normal corneas and four subjects with keratoconus were studied. In the initial analysis it was found that a number of the subjects showed significant changes in corneal topography as accommodation changed. However further analysis showed a significant group mean excyclotorsion of the topography maps for both accommodation stimuli compared with the 0 D stimulus. When the excyclotorsion was accounted for, no clear evidence of statistically significant changes in corneal topography as a result of accommodation were found. A small ocular excyclotorsion typically accompanies accommodation and this changes the relative orientation of the topography of the cornea. To investigate the effects of eyelid pressure on corneal shape and corneal aberrations during reading, twenty young subjects with normal ocular health were recruited. Cornea1 topography of one eye was measured with a videokeratoscope prior to reading and then again after a 60 minute reading task. Twelve of the twenty corneas showed significant changes in central topography immediately following reading. The location of the changes corresponded closely to the position and angle of the subject's eyelids during reading. Within the central region of the cornea there were significant changes in corneal wavefront Zernike coefficients, the root-mean-square error, overall refractive power and astigmatism. The changes observed in corneal topography appear to be directly related to the force exerted by the eyelids during reading. These findings may have important implications for the definition of refractive status and may also aid in the understanding of the relationship between reading and the development of refractive errors. To study whether corneal distortions after reading significantly differ between refractive error groups, corneal aberrations were measured before and after a period of reading, for a group of ten young progressing myopes and a group of ten young stable emmetropes. The major difference between the two groups was the location and magnitude of the corneal distortions, which had a significantly larger effect on central corneal optics in the myopic group compared to the emmetropic group. A significantly smaller palpebral aperture for the myopic group in the reading gaze position was the cause of this difference. The experiments described in this thesis have shown that numerous corneal characteristics can change due to eyelid forces during near work. The eye was shown to undergo a small cyclotorsion during higher levels of accommodation. There was a shift in direction of against the rule astigmatism of the cornea following reading and a change was found for primary vertical coma and trefoil. The changes in corneal shape following reading appear to be different in myope versus emmetropic refractive error groups. These findings are important for our understanding of the stability of the refractive error of the eye and could have important implications for refractive error development.

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.

This thesis examines problems in electron diffraction and related areas of theoretical optics. It begins with a study of the phase of a quantum mechanical wave function and the behaviour of phase vortices and vortex cores. Several rules for vortex core evolution are given and simulated vortex trajectories are studied. These simulations show that in electron microscopy at atomic resolution and in other similar situations, vortices occur in the wave functions very frequently. This means any image processing methods which deal with the wave function phase must permit vortices to occur. In this context a number of methods of phase retrieval are compared and evaluated. The criteria of evaluation are the accuracy of the phase retrieval, its ability to cope with vortices, its numerical stability and its required computational resources. The best method is found to be an iterative algorithm similar in approach to the Gerchberg-Saxton method, but based on a through focal series of images. / Using this phase retrieval method as an essential tool, the thesis continues with a study of inverse problems in electron optics. The first problem considered is that of using a set of images taken to characterise the coherent aberrations present in a general imaging system. This problem occurs in many areas of optics and is studied here with a focus on transmission electron microscopy. A method of using software to simultaneously determine aberrations and subsequently remove them is presented and tested in simulation. This method is found to have a high level of accuracy in aberration determination. The second inverse problem studied in this thesis is the inversion problem in dynamical electron diffraction. This problem is solved for a periodic object, giving an accurate and unique solution for the projected potential in the multiple scattering case. An extension of this solution to objects which are non-periodic in the direction of the incident wave is investigated. Finally a model computation solving the general inversion problem for dynamical diffraction in an aberrated transmission electron microscope is performed, illustrating this and previous material and summing up the advances presented in this work.

Thesis--Copenhagen University. / Summary in Danish. Bibliography: p. 125-129.

Thesis--Copenhagen University. / Summary in Danish. Bibliography: p. 125-129.