Abnormal focal macular electroretinograms in eyes with idiopathic epimacular membrane

PURPOSE: To study the functional state of the retina beneath an epimacular membrane by means of focal macular electroretinography, METHODS: Focal macular electroretinograms of 30 consecutive patients (age 2 5 to 75 years) with unilateral idiopathic epimacular membrane were recorded prospectively, The amplitudes and implicit times of the a and b waves and the oscillatory potentials (O1, O2, O3) recorded from the eye with idiopath ic epimacular membrane were compared with those of the normal fellow eye. RESULTS: There was a statistically significant reduc tion in the amplitude of the a wave (P < .001), the b wave (P < .001), and the oscillatory potent ials (O1 + O2 + O3; P < .001) of the affected eyes. The reduction of the b- wave amplitude was significantly greater than that of the a wave, resulting in a lower b/a wave ratio (P = .003) in the affected eyes. The reduction i n the amplitude of the oscillatory potentials was significantly greater tha n that of the other two components (P < .001). The implicit times were sign ificantly prolonged for the a wave (P < .001), the b wave (P = .004), and O 3 (P < .001). There was a significant correlation between relative b-wave a mplitude (affected/normal fellow eye) and the visual acuity (r = -0.50, P = .007). These findings were similar to those we reported for eyes with apha kic cystoid macular edema. CONCLUSIONS: The focal macular electroretinograms in eyes with epimacular m embrane disclosed abnormalities that were similar to those of eyes with cys toid macular edema. This suggests that the epimacular membrane probably ind uced damage to the neurons in the inner retinal layers, Dysfunction of thes e neurons is one possible cause of visual impairment in this disease. (C) 1 999 by Elsevier Science Inc. All rights reserved.