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A. D. McTrusty, G. J. Kennedy, N. C. Strang, V. Manahilov, L. S. Gray; Foveal Aliasing is Orientation and Luminance Dependent. Invest. Ophthalmol. Vis. Sci. 2010;51(13):965.
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© ARVO (1962-2015); The Authors (2016-present)
Using measures of grating acuity, previous studies have shown that axial elongation in myopic eyes may cause aliasing due to neural undersampling, even in foveal vision. It is also known that measures of grating acuity can vary with orientation and level of illumination. The purpose of this study was to measure foveal aliasing in myopia and determine the effect of viewing conditions upon the measurements.
Measures of grating acuity were obtained from the right eyes of 20 subjects with refractive errors ranging from 0D to -11.00D (age 17-35 years). Stimuli were high contrast (90%) sinusoidal gratings, subtending 2 degrees at a viewing distance of 6m. Under photopic conditions (30 cdm-2) we compared detection acuity with resolution acuity using gratings of various orientations and separations of test and reference grating (89°/91°,88°/92°, 86°/94°, 82°/98°, 80°/100°, 70°/110°,90°/180°,45°/135°). Detection and resolution acuity was also measured under mesopic (0.37 cdm-2) conditions in a subgroup of 4 subjects (2 emmetropes and 2 myopes) who exhibited a significant difference between detection and resolution acuity when measured in photopic conditions.
Resolution acuity improved with increasing separation of the test and reference orientations . Mean group difference between detection and resolution acuities was greatest (9.88 ±4.99cpd, p<0.05), when the test and reference orientations used to measure resolution were separated by 20° (presented at 800 and 1000) and smallest (0.58 ±2.03cpd, p>0.05) when presented at 900/1800. In our subgroup, no significant differences between detection and resolution acuity were found in mesopic conditions
The orientation dependent nature of foveal aliasing in both myopes and emmetropes may be explained by orientation specific cortical processing. The absence of foveal aliasing in mesopic conditions is a consequence of functional changes occurring in the receptive fields at lower luminances.
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