Two types of visual dysfunction in autosomal dominant retinitis pigmentosa

Visual thresholds and rhodopsin levels were determined in nine subjects with autosomal dominant retinitis pigmentosa. The subjects fell into two groups, corresponding to two subtypes of the disease revealed by two-color, dark-adapted static perimetry. In the first of these subtypes, rod-mediated function was variably reduced and was accompanied by a corresponding reduction in cone function in the same retinal region. Dark-adapted threshold elevations varied in a way consistent with decreased quantal absorption by the rods as a result of reduced rhodopsin levels. In the second subtype, rod function was greatly reduced or absent throughout the retina, while cone function was much less severely affected. Although the levels of rhodopsin were only about half of normal, they were much too great to account for the visual threshold elevations on the basis of decreased probabilities of absorption by the visual pigment. Rhodopsin regeneration appeared to follow normal kinetics in patients from both groups. The results indicate that the examples of the two psychophysical subtypes of AD RP investigated here have very different disease manifestations.