No description available.

The central purpose of this research has been to examine the possibility of the plasticity of individual saccadic parameters and to identify their patterns of covariation. Experiments using trial-by-trial feedback or continuous on-going feedback methods demonstrated that the saccadic generator can prolong the duration of a saccade above normal levels. However, slowed peak velocities were only evident with continuous feedback. The results showed that although continuous feedback was a more effective method for inducing modifications of saccade trajectories, the effects of trial-by-trial feedback schedules were enhanced by distributing the training over several days. The instructions to produce slow saccades caused a 'staircase' pattern of eye movements in which a continuous sequence of hypometric saccades was manifested. These saccades had latencies 400-600 msecs longer than normal visually controlled eye movements. Detailed measurements (chapter 4) of the latencies of the saccadic components indicated that each component was programmed independently. In chapter 5 the Gurevich claim that a saccade velocity depends only on the spatial magnitude of the saccade was tested by measuring saccades of equivalent amplitudes to targets which varied in movement duration and velocity. The accuracy of saccades but not their peak velocities or durations was sensitive to manipulations in the temporal characteristics of the target. Experiments in chapter 6 showed that the use of spatial signals in the aiming of a saccade can be systematically controlled. When subjects were trained for several days in a visual discrimination task the accuracy of the initial saccadic movement increased over time. The results of these experiments seriously question the Young and Stark (1963b) ballistic model and other formulations (Westheimer, 1954b, 1973; Yarbus, 1967) which assume that the saccadic system operates according to stereotyped mechanisms.

Neste trabalho foi desenvolvido um novo instrumento para monitoramento computadorizado da curvatura da região central anterior da córnea humana durante cirurgias refrativas. Através da projeção de um disco de Plácido na córnea, imagens dos reflexos são digitalizadas e processadas. Algoritmos baseados em técnicas de visão computacional e óptica geométrica determinam a curvatura da região central (-7 mm em diâmetro), com alta precisão e desempenho. Mapas coloridos com códigos de cor em dioptrias (proporcionais ao inverso do raio de curvatura) são gerados para auxiliar o oftalmologista durante a cirurgia. / In this work we have developed a new instrument for computerized monitoring of corneal central curvature during surgery. By projecting Placido Rings on the cornea, images of the reflections are digitized and processed. Algorithms based on computational vision and optical geometry determine the central curvature (-7 mm in diameter), with high performance and precision. Color coded maps in diopters (proportional to the inverse of the radius of curvature) are generated to aid the ophthalmologist during surgery.

Neste trabalho foi desenvolvido um novo instrumento para monitoramento computadorizado da curvatura da região central anterior da córnea humana durante cirurgias refrativas. Através da projeção de um disco de Plácido na córnea, imagens dos reflexos são digitalizadas e processadas. Algoritmos baseados em técnicas de visão computacional e óptica geométrica determinam a curvatura da região central (-7 mm em diâmetro), com alta precisão e desempenho. Mapas coloridos com códigos de cor em dioptrias (proporcionais ao inverso do raio de curvatura) são gerados para auxiliar o oftalmologista durante a cirurgia. / In this work we have developed a new instrument for computerized monitoring of corneal central curvature during surgery. By projecting Placido Rings on the cornea, images of the reflections are digitized and processed. Algorithms based on computational vision and optical geometry determine the central curvature (-7 mm in diameter), with high performance and precision. Color coded maps in diopters (proportional to the inverse of the radius of curvature) are generated to aid the ophthalmologist during surgery.

No description available.

Yes / Purpose: To demonstrate that silent substitution stimuli can be used to generate electroretinograms (ERGs) that effectively isolate rod photoreceptor function in humans without the need for dark adaptation, and that this approach constitutes a viable alternative to current clinical standard testing protocols. Methods: Rod-isolating and non-isolating sinusoidal flicker stimuli were generated on a 4 primary light-emitting diode (LED) Ganzfeld stimulator to elicit ERGs from participants with normal and compromised rod function who had not undergone dark-adaptation. Responses were subjected to Fourier analysis, and the amplitude and phase of the fundamental were used to examine temporal frequency and retinal illuminance response characteristics. Results: Electroretinograms elicited by rod-isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30 Hz. Responses are optimal between 5 and 8 Hz and between 10 and 100 photopic trolands (Td). There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. Analysis of signal-to-noise ratios reveals significant differences between subjects with normal and compromised rod function. Conclusions: Silent substitution provides an effective method for the isolation of human rod photoreceptor function in subjects with normal as well as compromised rod function when stimuli are used within appropriate parameter ranges. Translational Relevance: This method of generating rod-mediated ERGs can be achieved without time-consuming periods of dark adaptation, provides improved isolation of rod- from cone-based activity, and will lead to the development of faster clinical electrophysiologic testing protocols with improved selectivity.

The visual quality effects from the dynamic behavior of the tear film have been determined through measurements acquired with a high resolution Twyman-Green interferometer. The base shape of the eye has been removed to isolate the aberrations induced by the tear film. The measured tear film was then combined with a typical human eye model to simulate visual performance. Fourier theory has been implemented to calculate the incoherent point spread function, the modulation transfer function, and the subjective quality factor for this system. Analysis software has been developed for ease of automation for large data sets, and outputs movies have been made that display these visual quality metrics alongside the tear film. Post processing software was written to identify and eliminate bad frames. As a whole, this software creates the potential for increased intuition about the connection between blinks, tear film dynamics and visual quality.

Failing eyesight causes a dramatic change in life. The aim of this project is to help people with large central visual field loss to better utilize their remaining vision. Central visual field loss means that the person has to rely on peripheral vision since the direct vision is lost, often due to a dysfunctional macula. In these cases, a full restoration of vision would require replacement or repair of the damaged retinal tissue, which is not yet possible. Instead, the present study seeks to improve peripheral vision by enhancing the image quality on the remaining functional part of the retina by optical corrections. The off-axis optics of the human eye often suffers from large optical errors, which together with the lower sampling density of the retina explain the limited visual function in the periphery. The dominating aberrations are field curvature and oblique astigmatism, which induce an effective eccentric refractive error. However, the irregular character of the aberrations and the limited neural function in the periphery will make it difficult to find the optimal refractive correction; the conventional subjective refraction, for example, is not suitable for subjects with large central visual field loss. Within the work of this thesis a Hartmann-Shack wavefront sensor has been constructed for oblique aberration measurements. Wavefront sensing is an objective method to assess detailed information about the optical errors in the human eye. Theory and methods have been developed to allow accurate off-axis measurements of the large aberrations, enable eccentric fixation, and handle the elliptical pupil. The study has mainly concentrated on sphero-cylindrical correction of peripheral vision. Peripheral resolution and detection acuity thresholds have been evaluated for seven subjects with central visual field loss and ten control subjects with normal vision. Five of the subjects with field loss showed improved resolution acuity with eccentric refractive correction compared to their habitual central correction, whereas little change was found for the control subjects. These results demonstrate that correction of peripheral optical errors can be beneficial to people with large central visual field loss in situations where a normal healthy eye does not experience any improvements. In conclusion, it is worthwhile to investigate the peripheral refractive errors in low-vision rehabilitation of central visual field loss and prescribe spectacle correction when those errors are large. / QC 20100809

No description available.

Since the characterization of the eye's monochromatic aberration fluctuations in 2001, the power spectrum has remained the most widely used method for analyzing their dynamics. However, the power spectrum does not capture the complexities of the fluctuations. We measured the monochromatic aberration dynamics of six subjects using a Shack-Hartmann sensor sampling at 21 Hz. We characterized the dynamics using techniques from chaos theory. We found that the attractor embedding dimension for all aberrations, for all subjects, was equal to three. The embedding lag averaged across aberrations and subjects was 0.31 +/- 0.07 s. The Lyapunov exponent of the rms wavefront error was positive for each subject, with an average value of 0.44 +/- 0.15 microm/s. This indicates that the aberration dynamics are chaotic. Implications for future modeling are discussed.