Acuity-Luminance Function in Achromatopsia and in Progressive Cone Degeneration: Factors Related to Individual Differences in Tolerance to Bright Light

¹ Department of Ophthalmology, Wilmer Ophthalmological Institute, The Johns Hopkins University, School of Medicine, Baltimore, Md. 21205
² Department of Ophthalmology, Wilmer Ophthalmological Institute, The Johns Hopkins University, School of Medicine, Baltimore, Md. 21205.

The variation of acuity with luminance was measured in 12 subjects with selective impairment of cone function, including complete and incomplete achromatopsia and progressive cone degeneration. Other tests of visual function were given to identify the types of retinal receptors at the fixation point. These tests included measurement of the rate of dark adaptation with blue and white stimuli and, in the case of patients with a progressive cone degeneration, examination of the central visual field with red and blue test targets. A biphasic foveal adaptation curve in which both sections have the same relative sensitivity to blue and white was taken as evidence for two types of receptor, both of which have the spectral sensitivity of rhodopsin. These are designated for convenience as photopic and scotopic rods. When the relative sensitivities to blue and to white differed for the two sections of the adaptation curve, this was taken as evidence for the presence of both cone and rod receptors at the fixation point. Intolerance to bright light, as measured by the acuity-luminance function, was particularly marked in those who had only scotopic rods at the fovea. The decrease in acuity in bright light was less severe in patients who had either photopic rods or cones at the area used for fixation.

Note:

Presented in part at the 1972 meeting of the Association for Research in Vision and Ophthalmology, Sarasota, Fla.

Key Words: achromatopsia • progressive cone degeneration • photophobia • photopic rods • dark adaptation

Submitted on May 31, 1972
Accepted on July 17, 1972