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D. Ivastinovic, R. Hornig, A. Langmann, H.-Jü. Adams, M. Velikay-Parel; The Suitability of Normally Sighted Subjects With a Pixelized Vision Simulator in Low Vision Testing. Invest. Ophthalmol. Vis. Sci. 2007;48(13):670.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal implants will create artificial vision. Since there are no adequate tests to document the progress of the patients vision we established a visual acuity test (a modified grating test) and a visual function test (the Graz mobility test). Previous studies proved that these tests are adequate to differentiate and grade the low vision of patients with retinitis pigmentosa. Since the tests should be used repeatedly in retinal implants, further studies to prove the consistency of the performance in repeated testing need to be conducted. However the availability of low vision patients ready to take part in this study is very restricted. We therefore investigated if normally sighted subjects, whose visual acuity was reduced by a pixelized vision simulator, are suitable for these low vision tests.
10 normally sighted subjects were enrolled. Their visual acuity was reduced by a pixelized real time vision simulator. Two different adjustments were used for our study, 80 pixels and 224 pixels simulating a visual acuity of hand motion and 20/800. In the modified grating test, black and white bars of the same width were projected on a white screen with the size of the bars reducing over time. The subjects were asked to specify the direction of the bars until the direction could not be recognized. A four alternative forced choice test method was used. The visual function was tested with the Graz mobility test consisting of four different, structurally similar and relatively short mazes with 11 obstacles of various sizes. The subjects passed through each course several times recording their walking speed as an index of performance.
Significant differences could be found between 224 and 80 pixels in the modified grating test (paired samples t-test, p<0.01) whereas no significant differences were found in walking speed with 224 and 80 pixels (Wilcoxon test, p=0.2).
Results show that the subjects could differentiate the two vision levels in the modified grating test. However visual function testing is a more complex task than visual acuity testing. Normally sighted subjects were not showing any difference between the two vision levels when performing the Graz mobility test. In contrast, previous studies proved that low vision patients showed significant differences depending on their level of low vision. The adaptation to the reduced vision which can be achieved within a few hours by normal sighted subjects wearing the pixel simulator is not sufficient to approximate the performance of low vision patients in function testing.
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