The dyschromatopsia of optic neuritis is determined in part by the foveal/perifoveal distribution of visual field damage

Most hypotheses of acquired dyschromatopsia invoke the mechanism of selective damage to specific components of the afferent visual system to explain the predominance of red-green and blue-yellow hue-discrimination defects found in neural and retinal disorders, respectively. However, this pattern of hue-discrimination disturbance in ocular disease may vary. There are frequent exceptions which are inadequately explained by existing hypotheses. In an effort to explain the pattern and pathogenesis of acquired dyschromatopsias better, the authors examined patients with nonproliferative diabetic retinopathy (DR) and late-stage retrobulbar neuritis (RBN) using age-corrected Farnsworth-Munsell 100-hue testing and threshold static perimetry. As expected, most DR eyes showed some degree of relative blue-yellow dyschromatopsia (89%) with few showing a greater weighting towards red-green dyschromatopsia (11%). However, an approximately equal number of RBN eyes had a relative blue-yellow (48%) versus red-green dyschromatopsia (52%). For RBN, the authors found a strong association between the spatial distribution of field defect and the type of relative hue-discrimination disturbance. Eyes with greater field depression at the fovea relative to the perifovea showed a relative preponderance of red-green dyschromatopsia (68%) as opposed to blue-yellow dyschromatopsia (32%), whereas eyes with greater relative perifoveal impairment showed a relative preponderance of blue-yellow dyschromatopsia (100%). This relationship between the relative spatial distribution of visual field damage and the relative hue-discrimination deficit in RBN was statistically significant (P = 0.002). Such an association was not found for DR. Rather, a preponderance of relative blue-yellow dyschromatopsia was present in nearly all DR eyes, without regard to the spatial distribution of visual field defect. Our findings suggest that the spatial distribution of damage to the foveal and perifoveal visual field is an important determinant of the resulting hue-discrimination defect in RBN but not in DR. There are fundamentally different underlying mechanisms of color vision impairment in these two classes of disease.