Changes in multifocal electroretinograms immediately after transpupillary thermotherapy

Purpose : To monitor retinal function immediately after transpupillary thermotherapy (TTT) for subfoveal choroidal neovascularization (CNV) using multifocal electroretinograms (mfERGs). Methods : mfERGs were recorded before and after TTT (wavelength, 810 nm; diameter, 3 mm; duration, 60 seconds; power, 350 mW) in 13 eyes of 13 patients with CNV. mfERGs were recorded from 7 hexagonal stimulation areas; the central hexagon covered the laser-irradiated area and the surrounding areas were free from irradiation. Each recording was completed within 1 minute, and recording was repeated intermittently during the first 60 minutes after TTT. Results : The amplitudes of ERGs recorded from irradiated areas were reduced 1 minute after TTT (p<0.01, Student's t-test) and then recovered. The peak delay was noted 15 minutes after TTT (p<0.01) and recovery lasted until 60 minutes after TTT. Focal ERGs in the non-irradiated areas were unchanged. Conclusions : mfERGs reflected alterations in retinal function immediately after TTT that had been thought to induce subthreshold changes. The early reduction in mfERG amplitude that occurred at 1 minute was probably due to increase in temperature during TTT, as previously reported for focal flicker ERGs. The time of the peak increase about 15 minutes after TTT indicates that it may be caused by a biological reaction to TTT.