The relationship between visual sensitivity and rhodopsin density in retinitis pigmentosa.

Rhodopsin density and absolute threshold were determined in 11 patients with retinitis pigmentosa (RP) and nine normal subjects. In eight patients with familial histories suggesting recessive inheritance, the retinal areas studied showed marked decrease in sensitivity which was related to rhodopsin loss, probably via a log-linear relationship. The other three patients showed absolute thresholds that were linearly related to rhodopsin density, suggesting that sensitivity loss was determined by the decrease in quantal absorption resulting from rhodopsin loss. The results indicate that RP patients can be classified into two categories according to the effects of rhodopsin loss on rod sensitivity. These categories may correspond to different genetic groups. Furthermore, this differentiation may, in fact, reflect different underlying disease mechanisms.