Cone positive off-response in normal and dystrophic cats

Light-adapted cone ERG in response to white stimuli with long duration (200 ms) was studied in seven normal cats and six cats with early to moderate, inherited retinal dystrophy. The stimuli typically elicited an ERG consisti ng of an a- and b-wave in response to light onset, whereas light-offset was followed by a cornea-positive d-wave and subsequent negative dip and occas ionally a second positive peak in both normal and dystrophic cats, although b- and d- waves had less distinct peaks in cats with moderately advanced r etinal dystrophy. Linear regression models indicated a positive correlation between d-wave amplitude and stimulus luminance, whereas a negative correl ation was found between amplitude and background light luminance in normal cats. The d-wave implicit time was independent of both stimulus and backgro und light luminance in normal cats. The d-wave amplitude was not significan tly different in dystrophic cats, whereas the implicit time was increased w hen affected cats were compared to normal cats. The significant increase in implicit time in dystrophic cats could not be explained with a reduced sen sitivity of the off-pathway to background or stimulus light. This is suppor ted by the finding that d-wave amplitude was not significantly altered in e arly to moderately advanced dystrophic cats.