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T.J. Van Den Berg, J.E. Coppens; An Individual-dependent Recognition Component in Visual Acuity . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2781.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In a young ocularly normal population best refracted VA values ranging from 1 to 3 can be found. We would like to better understand this large variation in visual acuity among healthy eyes. Partly it might stem from purely optical differences. Part of the spread might also be caused by neuronal differences between individuals. In the present study a non-optical component in acuity was investigated. Methods: Best refracted VA of 77 eyes was measured with Landolt C optotypes. The optotypes were either ‘sharp' or blurred with Gaussians of various widths: σa=8.48', 4.24' and 2.12'. With the larger blurs (8.48' and 4.24') optical differences between the eyes are irrelevant for the retinal projection. So, differences in VA with these blurs must be attributed to a non-optical effect. Results: Standard deviation of log(MAR) in our subject group was 0.11 (unblurred optotypes). This variance could be subdivided in 3 components: With 8.48' as well as with 4.24' blurs standard deviation of log(MAR) was 0.06. Intrinsic retinal blur variation had a standard deviation of 0.08 log units. Measurement accuracy had a standard deviation of 0.03 log units. Difference in log(MAR) between the 8.48' and 4.24' blurred stimuli was 0.291±0.005 log units, close to a factor of 2 in correspondence with a scale invariance model: MAR ~ effective retinal blur = √(σi2+σa 2), with σi = intrinsic retinal blur of the eye. Log(MAR) values for the 2.12' blurred stimuli, predicted using this model, closely followed the actually found values. Conclusions: The MAR values are closely proportional to a value for equivalent blur of the stimulus, combining intrinsic blur of the eye and added blur. The proportionality factor is different between individuals and is a partial source of variance in acuities found in a healthy population. The scale invariance model allows introduction of ‘intrinsic retinal blur' as a measure of retinal image quality. View OriginalDownload SlideView OriginalDownload Slide
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