Oscillatory Potentials Measured With the Time-Slice MfERG Recording

Purpose: To investigate oscillatory potentials (Ops) with the multifocal electroretinogram (mfERG) using the time-slice (TS) paradigm introduced by Menz M et al. (ARVO 2004/2005 E-abstracts 4228/3438).\ud Methods: We recorded the TS mfERG in 10 healthy young subjects (aged between 28 to 38 years), in one patient (76 years) with early age-related maculopathy (ARM) and in one patient (age 36) with Retinitis pigmentosa (RP). The recording consisted of 10 dark video frames followed by a series of m-sequence modulated test frames (n=6) probing the multifocal responses at intervals of 13.3 ms. In the first experiment the stimulus display consisted of 61 hexagons presented on a CRT monitor (probe flash: 6.4 cd*s/m2, mean adaptation level: 240 cd/ m2). In a second experiment only 19 hexagons were stimulated according to the TS mode and the surrounding hexagons remained dark (masked) to estimate the influence of lateral interaction effects. Data were averaged and analysed in five concentric rings.\ud Results: In the first experiment the response to probe 1 consisted of four distinct OPs with mean peak implicit times (ITs) of 13.3 (±1.4 SD) ms, 20.1 (±1.6 SD) ms, 27.5 (±2.0 SD) ms and 35.3 (±2.0 SD) ms, respectively. These became slightly faster (Op1: 12.4 (±0.99 SD) ms, Op2: 18.4 (±0.7 SD) ms, Op3: 25.0 (±1.1 SD) ms, Op4: 32.0 (±1.7 SD) ms) and smaller in amplitude towards ring 5. In the second, masked experiment the four Ops were distinct in the center (mean implicit times 15.0 (±2.2 SD) ms, 21.7 (±2.2 SD) ms, 30.0 (±1.4 SD) ms 36.6 (±1.4 SD) ms) but smaller in the periphery. The responses to probes 2-6 did not reveal clearly distinguishable Ops in either experiment. The ARM patient showed slightly delayed responses to probe 1 with ITs of 15.8 ms, 21.7 ms, 27.5 ms, 34.2 ms for the central early Ops and small to non recordable peripheral Ops (rings 3-5). Similarly, the RP patient demonstrated distinct central Ops and poor peripheral Ops. Also, Ops only became evident after about 40 ms of adaptation in the RP patient.\ud Conclusion: In healthy subjects Ops are better indicators of function in the central retina than in the periphery and are poorly recordable after local adaptation. Decreased peripheral Ops in the masked experiment suggest that lateral interaction effects largely contribute to peripheral Ops in healthy subjects. Similar findings in ARM and RP patients without masking the surrounding hexagons seem to indicate that lateral retinal processing is affected in both conditions