Background: To characterize the electroretinographic response of the macula by multifocal electroretinography (mfERG) in patients with type 2 idiopathic macular telangiectasia (MacTel).
Methods: A prospective study of mfERG in patients with type 2 MacTel was conducted from April 2009 to November 2009. mfERGs were recorded using a visual evoked response imaging system (MonElec2, Metrovision, Perenchies, France). The International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines were followed. Patients with type 2 MacTel confirmed by fundus fluorescein angiography without subretinal neovascularisation were included. For recording purposes, 61 stimulus hexagonal elements were used. The first-order kernel mfERG responses were analyzed. Individual mfERG responses for the hexagons were grouped into concentric rings centered on the fovea for analysis (< 2, 5-10, 10-15 and >15°). Student's t-test and Mann-Whitney U test and linear regression analysis was performed with STATA ver 11.1 (StataCorp, College Station , TX, USA).
Results: Twenty eight eyes of 14 patients and 20 eyes of ten normal controls were included in the study. The mean logMAR visual acuity of the patients was 0.51 (Snellen equivalent 20/63). The mean N1 amplitude (nv/deg(2)) of patients were significantly reduced compared to controls and were as follows: 8.91 ± 14.00 vs 43.44 ± 9.55 (p < 0.0001) in less than 2°, 9.24 ± 10.47 vs 22.00 ± 3.87 (p < 0.0001) in 5-10°, 8.57 ± 10.02 vs 15.24 ± 1.89 (p < 0.0001) in 10-15°, and 7.03 ± 6.52 vs 12.47 ± 2.62 in > 15° (p < 0.001). The mean P1 amplitude (nv/deg(2)) was also significantly reduced in patients compared to controls and was as follows: 27.66 ± 37.44 vs 96.20 ± 12.41 (p < 0.0001) in less than 2°, 22.61 ± 19.38 vs 53.78 ± 9.79 (p < 0.0001) in 5-10°, 18.75 ± 20.21 vs 35.22 ± 4.16 (p < 0.001) in 10-15°, and 17.10 ± 12.54 vs 25.71 ± 3.93 (p < 0.001). The implicit time of N1 and P1 were also delayed significantly in all the rings. The mean central foveal thickness assessed by optical coherence tomography (OCT) scan was 84.78 ± 45.12 μm. There was poor correlation between mfERG amplitudes or implicit times with either the visual acuity or OCT central thickness.
Conclusion: mfERG showed significant reduction in amplitudes and implicit times of the waveforms in patients with type 2 MacTel in all the rings, suggesting a more generalized affection of the macula. The maximum reductions were seen in the <2(o) rings. Although there was poor correlation between the visual acuity and the amplitudes a of the waveforms, mfERG is a useful investigative modality for functional assessment of macula in type 2 MacTel patients.