Abstract
Purpose: :
The eye’s ability to detect and distinguish fine objects requires optimal sampling array of cones, which relies on input of neighboring cones with similar and different spectral sensitivities. This is especially relevant in foveal vision, as all cones are of a single spectral type in red-green color deficient subjects, but two spectral types in trichromatic. This difference could be the basis for differences in acuity previously observed as reduced chromatic noise by fewer inputs results in increased visual acuity. However, the aberrations of the eye distort the visual image and do not allow proper assessment of the foveal mosaic. Adaptive optics allows for the direct testing of this sampling mosaic, unhindered by the aberrated optics of the human eye.
Methods: :
Color vision was tested in 7 color deficient and 6 trichromatic male observers using the Medmont C-100, AO-HRR, and Ishihara tests. Observers then completed a four alternative forced choice psychophysical task, testing visual acuity. This was done using an adaptive optics equipped vision simulator. Threshold was then determined as average log MAR of the last 5 of 12 reversals.
Results: :
Color vision tests showed that observers had both protan and deutan phenotypes. The average C-100 score was +2.1 for deutans, -3.4 for protans, and -0.8 for normal observers. No difference was observed between normal and color deficient subjects in the visual acuity task. The average MAR for these groups was 0.669+/-0.074 (color deficient) and 0.636+/-0.054 (trichromat).
Conclusions: :
We observed little variation among our color-deficient observers, and no difference between protan and deutan observers. Previous studies found that multi-gene dichromats had better visual acuity than single gene dichromats and normals. While genetic information was not available on our subjects, future work combining genetic analysis and the AO-psychophysical tools used here will be necessary to examine more precisely the link between the X-linked opsin gene array and visual performance. There is precedence for mutations at this locus negatively affecting visual function, though this was in a single rare allele. It remains to be seen how more "normal" variation at this locus affects visual function.
Keywords: photoreceptors: visual performance • color vision • aberrations