Abnormal foveal spectral sensitivity in retinitis pigmentosa

The authors measured dark-adapted foveal spectral sensitivity functions in 30 patients with retinitis pigmentosa or Usher's syndrome, whose Snellen visual acuities were 20/30 or better. An analysis of variance of the spectral sensitivity functions (normalized at 575 nm) indicated a significant reduction in the patients' relative sensitivity at 450 and 475 nm compared with a group of 15 age-similar normal observers, while the patients' relative sensitivity at middle and long wavelengths was normal. A significant negative correlation between the patients' normalized sensitivity at 450 nm and their non-normalized sensitivity at 575 nm indicated that patients with a normal absolute sensitivity at 575 nm had the greatest reduction in relative sensitivity at 450 nm. The characteristics of the short-wavelength sensitivity loss suggest that it results from an increase in the effective optical density of the yellow macular pigment, rather than from a decreased sensitivity of a specific cone mechanism or an increased lens absorption.