Changes in multifocal electroretinograms induced by transpupillary thermotherapy

Objective: To determine retinal function after transpupillary thermotherapy (TTT) for subfoveal choroidal neovascularization using multifocal electroretinograms (mfERGs). Methods: Multifocal electroretinograms were recorded before and after TTT (wavelength, 810 nm; diameter, 3 mm; duration, 60 seconds; power, 350 mW) in 9 eyes in 9 patients with subfoveal choroidal neovascularizations. The stimulus consisted of 7 hexagons; the central hexagon covered the laser-irradiated area and the surrounding 6 hexagons covered the nonirradiated area. Each recording was completed within 1 minute, and mfERGs were recorded periodically during the first 60 minutes after TTT and also at 24 hours and 1 week after TTT. Results: The amplitude of mfERGs from irradiated areas was significantly reduced at 1 minute after TTT (P<.01) and then recovered soon. The peak time was prolonged at 15 minutes after TTT (P<.01), recovered to pre-TTT levels at 60 minutes, and then was prolonged again at 24 hours (P<.05) and 1 week (P<.05) after TTT. The mfERGs in nonirradiated areas were unchanged during the observational period. Conclusions: We found amplitude reduction in central focal ERGs at 1 minute after TTT, transient peak-time delay at 15 minutes, and a delay at 24 hours. Early reduction is probably directly caused by an increase in temperature during TTT as previously reported in focal flicker ERGs. Peak-time delays at 15 minutes and 24 hours may be caused by other factors, such as increased intracellular calcium (Ca ²⁺), the release of nitric oxide or heat shock proteins, vasodilation, or change in choroidal neovascularization. Our findings indicate that recording mfERGs may be a useful tool for evaluating TTT procedures.