Neural Compensation for Color Deficiency: Binocular Enhancement of Cone-Specific Color VEPs

Abstract

Purpose: Central nervous system (CNS) degeneration often precedes glaucomatous retinal changes suggesting that glaucoma is a CNS disease. Moreover, preservation of the binocular field in glaucoma as well as cognitive function in Alzheimer’s disease are mediated by CNS control.^1,2 Our purpose was to determine if comparable CNS control mechanisms operate developmentally to optimize function in hereditary color vision deficiency (CVD) by comparing binocular to monocular cone specific color VEPs.

Methods: Red (L), green (M) and blue (S) cone specific VEPs were recorded in pattern-onset mode with colored checkerboards on a grey background (L&M cone: 1 deg. checks, S cone: 2 deg., 2 onsets/sec., Diagnosys LLC). Display luminance and CIE chromaticity were transformed to cone contrasts to selectively stimulate L, M and S cones. Subjects included 17 color vision normal (CVN) and 11 hereditary red or green CVDs confirmed to be CVD on a battery of tests. The ratio of binocular VEP amplitude (N1-P1) to mean (RE & LE) monocular amplitude was used to quantify enhancement.

Results: CVDs showed binocular facilitation of VEP amplitude (enhancement >2X; mean = 3.1X) for the color corresponding to their CVD. Values exceeded enhancement for other cone types within CVDs (3.1X vs. 1.2X, p<0.003) and compared to CVNs (3.1X vs. 1.2X, p<0.007). Binocular facilitation of CVD VEPs remained high (2.4X) even when quantified as binocular amplitude/higher amplitude from right or left eyes (2.4X vs. 1.1X, p <0.008). Dichromatic CVDs did show an enhancement effect.

Conclusions: Hereditary CVDs with anomalous trichromacy show binocular facilitation of VEPs for the color corresponding to their CVD. This suggests neural compensation for CVD similar to preservation of function in glaucoma and Alzheimer’s disease. Other congenital anomalies and rod-cone, macular and/or corneal dystrophies may be subject to neural compensation. Elucidation of underlying mechanisms could lead to new treatments for visually debilitating disease.<br /> ¹Crish et. al, PNAS 2010;107:5196-5201. ²Sponsel et. al TVST 2014;1-13.