Simultaneously recorded macular and paramacular ERGs in diseases affecting the central retina

Macular and paramacular ERGs in response to two alternating checks (6 deg/side) obtained from a standard TV stimulator were recorded in 34 normal subjects and in 54 patients affected by different macular diseases. Macular ERG amplitude and the amplitude ratio between macular and paramacular ERGs (M/P ratio) were measured. In normals, the intersubjects' variability of macular ERG was comparable to that reported using different stimulation/recording techniques. Macular ERG amplitude (but not the M/P ratio) was significantly affected by age. In patients, the mean amplitude of macular ERG and the mean M/P ratio were significantly lower than normal values. At least one of these two parameters was abnormal in 78.5% of eyes with maculopathy. Both macular ERG amplitude and M/P ratio were significantly correlated with visual acuity. The present results indicate that simultaneous macular and paramacular ERGs can be easily and reliably recorded in clinical routine to evaluate macular function. This technique appears to be particularly sensitive in hereditary macular diseases in which photoreceptors are primarily involved.