Chromatic adaptation in Best’s macular dystrophy: implications for quantitative phenotyping and clinical staging

Abstract

Abstract: : Purpose: To analyze patterns of chromatic dysfunction under different adaptation backgrounds in Best Disease in a quantitative manner, in order to reassess the classic categorization of macular chromatic damage, and to investigate psychophysical–clinical correlations. Methods: Color contrast discrimination was measured using two different psychophysical strategies, based on the Cambridge Colour Test. The first measured performance along three main confusion lines and the second evaluated discrimination ellipses that were further fit using a custom made algorithm. The study was run in age–matched control (n = 41) and patient (n = 34) eyes. Results: Significant loss of performance was seen in all color axes in our patient population. The observed dysfunction increased monotonically with clinical staging and became significant already in Fishman stages II–III, as also confirmed by ellipse length and axis ratio measurements. The classically assumed preferential red–green Type I deficit was only true for stage IV and a quite different pattern was observed in earlier stages. When the adapting field was non–neutral, deterioration of performance was least prominent along the deutan axis and most significant along the tritan axis. Substantial chromatic dysfunction occurred even with relatively preserved visual acuity (VA). Still, significant negative correlations between all test parameters and VA could be found. Partial correlation analysis showed that protan/deutan loss was related to VA independently of tritan loss. Significant positive correlations were also found between lesion size and chromatic dysfunction. Conclusions: Chromatic discrimination is often impaired in Best disease, even when visual acuity is still spared. The classical categorization as a type I red–green deficit is only valid for the late disease stage and blue cone dysfunction is actually more prominent in initial disease stages and under chromatic adaptation conditions. Cut–off values may offer a promising quantitative clinical approach to study early involvement and progression in this macular disorder.

Keywords: adaptation: chromatic • color vision • macula/fovea