Blue (S) cone pathway vulnerability: a test of a fragile receptor hypothesis.

The vulnerability of the blue (S) cone pathways to retinal disease has been attributed by some to S (blue) receptors, which are said to be more susceptible to metabolic damage (the fragile receptor hypothesis). Other investigators have suggested postreceptoral causes. To test the fragile receptor hypothesis, a two-site model of the S cone system is presented, and a psychophysical procedure is described. Data from a patient with congenital stationary night blindness (CSNB) and a patient with retinitis pigmentosa (RP) demonstrate the feasibility of this approach. As expected from previous work, the data reinforce the conclusion that the primary defect in CSNB is at the level of the receptors. The data from the patient with RP are consistent with the fragile receptor hypothesis.