Retinal function following transpupillary thermotherapy for occult choroidal neovascularization in age‐related macular degeneration: a short‐term study by focal electroretinography

Abstract

To assess short-term changes in macular function after transpupillary thermotherapy (TTT) in patients with occult subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD), using focal electroretinography (FERG). Twenty-five patients with occult subfoveal CNV due to AMD were treated with TTT delivered using an infrared (810 nm) diode laser (spot size 3.0 mm, laser power 400-600 mW, duration 60 seconds). All patients were clinically evaluated before, 1 and 6 weeks after treatment. Snellen visual acuity (VA) was measured at each visit. Fluorescein angiography (FA) was performed at baseline and 6 weeks after TTT. Focal ERGs were recorded in all patients immediately before and 1 week after TTT in response to an 18-degree diameter, 41 Hz flickering spot (630 nm) centred on the fovea, presented on a steady background in Maxwellian view. A subgroup of 12 patients was also re-tested by FERG at 6-weeks post-TTT. No significant changes in mean FERG amplitude and phase were observed across the different recording sessions before and after TTT. One week after TTT, four patients had significant (> 2 SD from baseline variability) increases in FERG amplitude and/or phase advances, one had a decrease in amplitude and four had phase delays, compared to baseline. The remaining 15 patients had stable FERGs. Six weeks after TTT, four patients had significant increases in FERG amplitude and/or phase advances, four had decreases in amplitude and/or phase delays, and four had stable FERGs, compared to baseline. Improvement in FERG parameters after TTT was always associated with an improvement in VA and a decrease in exudation. Patients with post-TTT FERG deterioration had stable or deteriorated clinical pictures. At either 1 or 6 weeks post-TTT, the FERG amplitude increase was inversely correlated (p < 0.05) with the baseline FERG amplitude and VA. Three major conclusions can be drawn: in a short-term follow-up, TTT was not found to be associated with significant changes in macular function; FERG improvement was associated with VA improvement, and the increase in FERG amplitude was greatest in patients with the worst baseline acuity.