Title also in Chinese. / Abstract also in Chinese. / Thesis (M.B.A.)--Chinese University of Hong Kong. / Bibliography: leaves 101-102.

Thesis (Honors)--College of William and Mary, 2008. / Includes bibliographical references (leaves 45-53). Also available via the World Wide Web.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

No / Department of Health

<p>This study is concerned with the negative effects of wearing corrective lenses while using eye trackers, and the correction of those negative effects. The eye tracker technology studied is the video based real-time Pupil Center and Corneal Reflection method. With a user study, the wearing of eyeglasses is shown to cause 20 % greater errors in the accuracy of an eye tracker than when not wearing glasses. The error is shown to depend on where on the eye tracker viewing area the user is looking.</p><p>A model for ray refraction when wearing glasses was developed. Measurements on distortions on the image of the eye caused by eyeglass lenses were carried out. The distortions were analyzed with eye tracking software to determine their impact on the image-to-world coordinates mapping. A typical dependence of 1 mm relative distance change on cornea to 9 degrees of visual field was found.</p><p>The developed mathematical/physiological model for eyeglasses focuses on artifacts not possible to accommodate for with existing calibration methods, primarily varying combinations of viewing angles and head rotations. The main unknown in the presented model is the effective strength of the glasses. Automatic identification is discussed. The model presented here is general in nature and needs to be developed further in order to be a part of a specific application.</p><p> </p>

This study is concerned with the negative effects of wearing corrective lenses while using eye trackers, and the correction of those negative effects. The eye tracker technology studied is the video based real-time Pupil Center and Corneal Reflection method. With a user study, the wearing of eyeglasses is shown to cause 20 % greater errors in the accuracy of an eye tracker than when not wearing glasses. The error is shown to depend on where on the eye tracker viewing area the user is looking. A model for ray refraction when wearing glasses was developed. Measurements on distortions on the image of the eye caused by eyeglass lenses were carried out. The distortions were analyzed with eye tracking software to determine their impact on the image-to-world coordinates mapping. A typical dependence of 1 mm relative distance change on cornea to 9 degrees of visual field was found. The developed mathematical/physiological model for eyeglasses focuses on artifacts not possible to accommodate for with existing calibration methods, primarily varying combinations of viewing angles and head rotations. The main unknown in the presented model is the effective strength of the glasses. Automatic identification is discussed. The model presented here is general in nature and needs to be developed further in order to be a part of a specific application.

Abstract not available

PURPOSE: A recent study suggested that updated spectacles could increase fall rate in frail older people. The authors hypothesized that the increased risk may be due to changes in spectacle magnification. The present study was conducted to assess the effects of spectacle magnification on step negotiation. METHODS: Adaptive gait and visual function were measured in 10 older adults (mean age, 77.1 +/- 4.3 years) with the participants' optimal refractive correction and when blurred with +1.00, +2.00, -1.00, and -2.00 DS lenses. Adaptive gait measurements for the leading and trailing foot included foot position before the step, toe clearance of the step edge, and foot position on the step. Vision measurements included visual acuity, contrast sensitivity, and stereoacuity. RESULTS: The blur lenses led to equal decrements in visual acuity and stereoacuity for the +1.00 and -1.00 DS and the +2.00 and -2.00 DS lenses. However, they had very different effects on step negotiation compared with the optimal correction. Positive-blur lenses led to an increased distance of the feet from the step, increased vertical toe clearance and reduced distance of the leading heel position on the step. Negative lenses led to the opposite of these changes. CONCLUSIONS: The step negotiation changes did not mirror the effects of blur on vision, but were driven by the magnification changes of the lenses. Steps appear closer and larger with positive lenses and farther away and smaller with negative ones. Magnification is a likely explanation of the mobility problems some older adults have with updated spectacles and after cataract surgery.

No / PURPOSE: A computer-based interactive binocular treatment system (I-BiT) for amblyopia has been developed, which utilises commercially available 3D 'shutter glasses'. The purpose of this pilot study was to report the effect of treatment on visual acuity (VA) in children with amblyopia. METHODS: Thirty minutes of I-BiT treatment was given once weekly for 6 weeks. Treatment sessions consisted of playing a computer game and watching a DVD through the I-BiT system. VA was assessed at baseline, mid-treatment, at the end of treatment, and at 4 weeks post treatment. Standard summary statistics and an exploratory one-way analysis of variance (ANOVA) were performed. RESULTS: Ten patients were enrolled with strabismic, anisometropic, or mixed amblyopia. The mean age was 5.4 years. Nine patients (90%) completed the full course of I-BiT treatment with a mean improvement of 0.18 (SD=0.143). Six out of nine patients (67%) who completed the treatment showed a clinically significant improvement of 0.125 LogMAR units or more at follow-up. The exploratory one-way ANOVA showed an overall effect over time (F=7.95, P=0.01). No adverse effects were reported. CONCLUSION: This small, uncontrolled study has shown VA gains with 3 hours of I-BiT treatment. Although it is recognised that this pilot study had significant limitations-it was unblinded, uncontrolled, and too small to permit formal statistical analysis-these results suggest that further investigation of I-BiT treatment is worthwhile.

To determine the test-retest reliability of the Randot stereoacuity test when used as part of vision screening in schools. METHODS: Randot stereoacuity (graded-circles) and logMAR visual acuity measures were gathered in an unselected sample of 139 children (aged 4-12, mean 8.1+/-2.1 years) in two schools. Randot testing was repeated on two occasions (average interval between successive tests 8 days, range: 1-21 days). Three Randot scores were obtained in 97.8% of children. RESULTS: Randot stereoacuity improved by an average of one plate (ie, one test level) on repeat testing but was little changed when tested on the third occasion. Within-subject variability was up to three test levels on repeat testing. When stereoacuity was categorised as 'fine', 'intermediate' or 'coarse', the greatest variability was found among younger children who exhibited 'intermediate' or 'coarse'/nil stereopsis on initial testing. Whereas 90.8% of children with 'fine' stereopsis (</=50 arc-seconds) on the first test exhibited 'fine' stereopsis on both subsequent tests, only approximately 16% of children with 'intermediate' (>50 but </=140 arc-seconds) or 'coarse'/nil (>/=200 arc-seconds) stereoacuity on initial testing exhibited stable test results on repeat testing. CONCLUSIONS: Children exhibiting abnormal stereoacuity on initial testing are very likely to exhibit a normal result when retested. The value of a single, abnormal Randot graded-circles stereoacuity measure from school screening is therefore questionable.