Focal macular electroretinograms (ER-80; Kowa, Nagoya, Japan) were recorded before, and 3 and 6 months after, the surgery. The technique of recording FMERGs under direct fundus observation has been described in detail.
29,30 Briefly, after the patients' pupils were fully dilated with 0.5% tropicamide and 0.5% phenylephrine hydrochloride, a Burian-Allen bipolar contact lens electrode (Hansen Ophthalmic Development Laboratories, Iowa City, IA) was used to record the FMERGs. The size of the stimulus spot was 15° (
Fig. 1A), and the background light from the fundus camera (CF-60DSi; Canon, Tokyo, Japan) illuminated nearly the entire visual field. The luminance of the stimulus was 30 cd/m
2, and the background luminance was 1.5 cd/m
2. The position of the spot on the fundus was monitored during the recording with a modified infrared fundus camera (ER-80; Kowa). The responses were digitally bandpass filtered from 5 to 500 Hz for the a- and b-waves and from 50 to 500 Hz for the OPs. Five hundred responses were averaged at a stimulation rate of 5 Hz (Neuropack S1 MEB-9400; Nihon Kohden, Tokyo, Japan). The amplitudes of the a-waves, b-waves, and OPs and the implicit times of a-waves and b-waves of the FMERGs were analyzed. The a-wave amplitude was measured from the baseline to the first negative trough, and the amplitude of the b-wave was measured from the trough of the a-wave to the positive peak of the b-wave (
Fig. 1C). Similarly, the implicit time of the a-waves and b-waves was analyzed at the time of the trough of the a-wave and peak of the b-wave. For the OP amplitudes, we measured the amplitude of each OP from the trough to the peak (O1∼O3), and the sum of the O1, O2, and O3 amplitudes was used for the statistical analyses (
Fig. 1C).
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