Retinal sensitivity to flicker modulation: Reduced by early age-related maculopathy

PURPOSE. TO evaluate retinal, cone-mediated flicker sensitivity (CFS) in ag e-related maculopathy (ARM) by quantifying response gain and threshold of t he focal electroretinogram (FERG) to flicker modulation. METHODS. Nineteen patients with ARM (visual acuity greater than or equal to 20/30) and 11 age-matched control subjects were examined. Twelve patients had less than 10 soft drusen in the macular region and no hyper-/hypopigmen tation (early lesion). whereas seven had more than 20 soft drusen and/or fo cal hyper-/hypopigmentation (advanced lesion). Macular (18 degrees) FERGs w ere elicited by a sinusoidally flickering (41 Hz) uniform field (on a light -adapting background) whose modulation depth was varied between 16.5% and 9 4%. Amplitude and phase of the response's fundamental harmonic were measure d. RESULTS. In both control subjects and patients with ARM. log FERG amplitude increased with log stimulus modulation depth with a straight line (power l aw) relation. However, the slope (or gain) of the function was, on average, steerer in control subjects than in patients with either early or advanced lesions. Mean FERG threshold, estimated from the value of the log modulati on depth th:lt yielded a criterion response, did not differ between control subjects and patients with early lesions but was increased (0.35 log units ) compared with control subjects in those with advanced lesions. In both pa tient groups, but not in control subjects, mean FERG phase tended to delay with decreasing stimulus modulation depth. CONCLUSIONS. Retinal CFS losses call be detected in ARM by evaluating the F ERC as a function of flicker modulation depth. Reduced response gain and ph ase delays, with normal thresholds, are associated with early lesions. Incr eased response thresholds, in addition to gain and phase abnormalities, may reflect more advanced lesions. Evaluating CFS by FERC may directy, documen t different stages of macular dysfunction in ARM.