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M. G. Todorova, A. M. Palmowski-Wolfe, J. Flammer, S. Orguel; Amplitudes to Long Duration Stimuli in the Mf ERG of POAG. Invest. Ophthalmol. Vis. Sci. 2008;49(13):6095.
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Results from our preliminary analyses of the data (EVER 2006) showed significant latency delay of the PhNR-on in patients with primary open-angle glaucoma (POAG),confirming that the PhNR is affected in glaucoma. This study was performed to see if the amplitudes of the PhNR provide a sensitive measure of dysfunction in POAG.
On-off mfERGs were recorded from 30 POAG patients with glaucomatous visual field defects (MD >2.5 dB) and glaucomatous optic neuropathies: 15 NTG (mean age 55.1, SD 7.2); MD 6.4dB (SD 5.2) and 15 HTG patients (mean age 62.5, SD 9.1), MD 4.7dB (SD 4.0) and compared to those of 15 controls (mean age 54.7, SD 10.91).Recording parameters: LED stimulus screen (RetiscanTM), 61 segments, frame rate: 70Hz, Lmax: 180cd/m2, Lmin: 0cd/m2, filter: 10- 200 Hz. For each m-sequence step, the LEDs were either on or off for 100ms, followed by 100 ms off. Recording time: 11.68 min.The amplitudes of N1P1 and P1N2 following stimulus onset (-on) as well as following stimulus offset (-off) were analysed. The difference P1N2-N1P1 was calculated to estimate the PhNR-on&-off. This was analyzed for the overall response, in quadrants as well as in 4 small central and peripheral neighbouring areas per quadrant.In an attempt to reduce the inter-individual variability the N1P1/P1N2 ratios were also calculated.
Amplitude (N1P1, P1N2, PhNR) did not differ between NTG, HTG and control. This held true for the overall response, the quadrants, the small focal areas analyzed as well as for the amplitude ratio ((p>0,05) ANOVA - Huynh-Feldt, adjusted for age). In quadrants mean amplitudes in nV/deg^2 (SD) of the PhNR-on for controls, NTG, HTG patients were: -3.37 (± 2.42), -3.74 (± 2.37), -2.92 (± 2.41) (SN); -3.81 (± 2.52), -3.34 (± 2.31), -3.42 (± 1.59) (IN); -3.02 (± 2.02), -3.30 (± 2.15), -3.31 (± 1.80) (IT); -3.0 (± 2.87), -2.73 (± 3.82), -3.33 (±2.84) (ST); and of the PhNR-off : -0.76 (±1.74), 0.16 (± 2.30), -0.66 (± 1.46) (SN); -2.14 (± 1.69), 0.20 (± 1.78), 0.89 (± 2.12) (IN); -0.86 (± 2.22), -0.54 (± 1.89), -0.74 (±1.94) (IT); -0.32 (± 1.88), -1.16 (±2.5), -0.62 (± 1.46) (ST).The correlations between the amplitudes of N1P1, P1N2, PhNR and the mean sensitivity did not reach the significance level (Spearman bivariate test).
In contrast to previous studies, that reported a marked reduction in amplitude with only a slight increase in the PhNR latencies using a slow stimulation mfERG paradigm, the present study showed no significant reduction in amplitudes of the PhNR. This may be due to stimulus parameters differing between the studies in stimulus length, base interval and luminance or to the large variability encountered.
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