Similarities between Congenital Tritan Defects and Dominant Optic-Nerve Atrophy: Coincidence or Identity?*

Abstract

Dominant inherited optic atrophy is usually a stationary disorder with typical findings of optic-nerve pallor, abnormal distance acuity but essentially normal reading vision, minimal visual-field defect, and characteristic color confusions in the blue–green region of the spectrum. The severity of these is extremely variable, even within the same family. In patients with minimal disease, distance acuity may be close to normal and optic pallor may be so subtle that a definitive diagnosis cannot be made unless several affected members of a family are seen. An evaluation of ocular- and color-vision findings are presented for three pedigrees. Color tests included determination of the Rayleigh equation, the American Optical HRR plates, the Farnsworth–Munsell 100-hue test, and determination of netural points and chromaticity confusions. Our results suggest a strong similarity in color vision between previously reported congenital tritan defects and patients with dominantly inherited optic atrophy. Criteria distinguishing the two conditions are suggested. However, a perusal of the literature reveals that most congenital tritanopes were not adequately evaluated to rule out dominantly inherited optic atrophy. Therefore, the almost identical color-vision profiles and pattern of inheritance of the two conditions lead us to question the existence of congenital tritan defect as an independent entity.