Recovery of the Multifocal Electroretinogram During a Course of Photodynamic Therapy for Neovascular Age–related Macular Degeneration

Abstract

Abstract: : Purpose: Subfoveal choroidal neovascularisation (CNV) is a major cause of visual loss in age–related macular degeneration (AMD). Last year at ARVO (poster #3117) we presented multifocal ERG deficits in this patient group compared to a normal group. Photodynamic therapy (PDT) is a drug and laser treatment that can slow down progression of CNV under certain conditions. This study investigates the effect of PDT on the mfERG over 12–months of treatment. Methods: New patients attending a regional medical retina service with active subfoveal predominantly classic CNV secondary to AMD were recruited and the affected eye studied before receiving PDT treatment. If possible, testing was repeated three, six and 12 months later when the patient attended for follow–up assessment and treatment. mfERGS were recorded between 2 and 300Hz using DTL thread electrodes in response to 19 scaled hexagons over 40°. Responses were then digitally filtered between 1 and 50Hz and described by the P1 amplitude density and latency of three concentric rings. Each parameter was quantified within groups using the median and 95% confidence intervals (CIs). 95% CIs were also used to describe the difference in parameters between visits. Results: 51 patients were recruited before treatment. A discernable central segment mfERG (5° field) was recorded in 61% (31/51) of patients initially, 54% (14/26) of patients at their three–month follow up, and 74% (23/31) of patients at their six month follow–up. The 95% CI of the difference in three and six month response rates = –0.42 to 0.04%. Compared to pre–treatment measurements, central segment and ring 2 mfERG responses tended to be smaller three months after treatment (95%CI for central segment=–19.5 to 2.1 nV/º² and for ring 2=–5.7 to 2.3 nV/º²), and larger six months after treatment (95%CI for central segment =–0.1 to 19.8 nV/º² and for ring 2 = –2.2 to 16.2nV/º²) and 12 months after treatment. Conclusions: The mfERG deficits at three months post–PDT agree with the work of others and reflect a functional deficit in the central macula. The improvement shown from six months onwards has not previously been reported. This may reflect an improvement in central macular function, a conclusion supported by Pattern ERG measurements from the same patients. Eccentric fixation learning may be a confounding factor but the persistence of positive findings beyond 6 months suggest a treatment related effect.

Keywords: age-related macular degeneration • electroretinography: clinical • photodynamic therapy