Rod-cone interactions in night-blinding disease.

When rods are dark-adapted they reduce cone flicker sensitivity as though a low-pass filter had been inserted in the visual pathway. This process is exaggerated in certain individuals and accounts for their complaint of night blindness, though ordinary clinical testing shows no abnormality. This rod-cone interaction occurs in the ERG and is absent in disease of the outer retina, which argues that the pathway involved is via the horizontal cell feedback onto the cones. Various anomalies of rod-cone interaction can be seen in retinitis pigmentosa. These suggest that it is the rod dark current which is responsible for inhibiting cones. The implications for the pathophysiology of retinitis pigmentosa are discussed.