Altered recovery of macular function after bleaching in Stargardt's disease-fundus flavimaculatus: Pattern VEP evidence

PURPOSE. To evaluate recovery of pattern visual evoked potentials (VEPs) after macular bleaching in patients with Stargardt's disease-fundus flavimaculatus (STD/FF). METHODS. Sixteen unrelated patients with STD/FF (age, 26 - 52 years; visual acuity, 0.2-1.0; phenotype I, n = 6; phenotype II, n = 8; or phenotype III, n = 2) and 15 age-matched control subjects were evaluated. VEPs were recorded in response to counterphased (two reversals per second) checkerboards (check size, 15 minutes; mean luminance, 80 cd/m²; contrast, 80%; stimulus field size, 18°) in baseline condition and at 20, 40, and 60 seconds after a 30-second exposure to a bleaching light (3.58 log photopic trolands), presented to the central (6° field) retina. In all patients, macular focal electroretinograms (FERGs) to an 18° uniform field, flickering at 41 Hz, were also recorded in separate sessions. RESULTS. At every postbleaching time, VEPs were delayed and suppressed in amplitude, compared with prebleaching values, in both patients and control subjects. However, the amount of delay and suppression was, on average, more pronounced (P <0.001) in patients than in control subjects. This difference was not accounted for by eccentric fixation in patients (n = 8) with central scotoma and was still substantial when only patients (n = 8) with normal visual field and acuity were considered. In individual patients, baseline FERG amplitudes correlated (r = -0.6, P <0.01) with the suppression of VEP amplitude at 40-seconds after bleaching. CONCLUSIONS. The results indicate an altered recovery of pattern VEPs after macular bleaching in STD/FF and suggest adaptation abnormalities in macular cone photoreceptors, occurring at disease stages with relatively preserved central visual field and acuity.