[The focal macular electroretinogram in idiopathic macular hole]

Focal macular electroretinograms (MERGs) were recorded with three different sizes of stimulus spots, 5 degrees, 10 degrees, and 15 degrees in diameter, in 14 patients with unilateral idiopathic macular hole. Their fellow eyes were normal in terms of visual acuity (> 1.0), MERG, and ophthalmoscopic macular findings. The amplitudes and implicit times of the a-wave, b-wave, and oscillatory potentials (OP) were compared between affected and fellow eyes. The amplitudes of the a-wave, b-wave and OP in the affected eyes were significantly smaller (p < 0.01) in all spot sizes. The rate of amplitude reduction of OP was significantly smaller than that of the a-wave and b-wave in the spots of 10 degrees and 15 degrees (p < 0.05). With the stimulus sizes to evoke the a-waves and b-waves of similar amplitudes between the affected and fellow eyes, OP always had a much larger amplitude in the affected eye. This result confirms our previous finding that the distribution of OP is relatively sparse in the fovea, becoming more dense than the a-waves and b-waves away from the fovea toward the parafovea and perifovea. The implicit time of the b-wave in the affected eyes was delayed significantly only in the 5 degrees spot (p < 0.01). The delay of the implicit time may result from the ring-shaped retinal detachment which always occurs in idiopathic macular hole.