Visual evoked cortical potential can be used to differentiate between uncorrected refractive error and macular disorders

The visual evoked cortical potential (VECP) is widely used to verify complaints of reduced visual performance and to identify the site of the disorder. In this study, we investigated the correlation between reduced visual acuity and VECP in volunteers with normal corrected visual acuity and in patients suffering from inherited macular degeneration or from age related macular degeneration (ARMD). Flash evoked VECP was not affected by the visual acuity in the cases of refractive error and in ARMD patients but was reduced in amplitude and delayed in implicit time in the patients suffering from inherited macular degeneration. The VECP elicited by pattern reversal checkerboard (PVECP) was not affected by the quality of the visual image in volunteers with uncorrected refractive error when checks of 60′ or larger were used but were considerably reduced in size and prolonged in implicit time for checks smaller than 15′. In both groups of patients suffering from macular dysfunction, pattern reversal VECP was very subnormal and was characterized by prolonged implicit time compared to values expected from their visual acuity. These findings indicate that the PVECP does not directly correlate with visual acuity but rather with foveal function. Therefore, we suggest that recordings of PVECP can be used to differentiate between refractive error and macular disorders as causing reduction in visual acuity when other clinical signs are missing or not available.