ADAPTATION OF ROD AND CONE ELECTRORETINOGRAMS IN THE ABYSSINIAN CAT HEREDITARY ROD CONE DEGENERATION

1. The rod ERG was studied during and after recovery from a full field adapting light (4.5 log td) considered to bleach most of the rhodopsin. At any stage in adaptation the dystrophic rod ERG was smaller and b-wave implicit time delayed compared to the normal. At equal response amplitudes, the b-wave implicit time was identical to normal. Sensitivity recovered at a similar rate but was one-tenth of normal. Rod b-wave implicit time tracked the same dark adaptation function and when compared at equal response amplitudes was identical in normal and dystrophic cats. 2. The cone ERG was studied at different steady levels of adaptation. Light adaptation decreased the sensitivity and implicit time of the cone ERG in normal and dystrophic cats. High levels of light adaptation were less effective in producing these effects in the dystrophic cat so that at 4 log td the cone ERG of the dystrophic was delayed in implicit time compared to normals. At all levels the cone ERG (b-wave) of dystrophic and normal cats was 5-10 ms faster than the human cone ERG. 3. The results suggest that there is no defect in the kinetics of dark adaptation or in the time-course of the transduction mechanism in this Abyssinian mutant. The ERG defects can be explained by reduced light absorption of rods and cones.