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Nataly Trang, Mathieu Gauvin, Robert K. Koenekoop, John M. Little, Jean-Marc Lina, Pierre Lachapelle; Oscillatory Potential Contribution to the ERG: A New Mean to Identify Disease Onset. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5684.
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© ARVO (1962-2015); The Authors (2016-present)
Oscillatory potentials (OPs) are often reported as small, high frequency, oscillations that are seen riding on the ascending limb of the ERG b-wave and most probably generated independently from the latter. An opposing view claims that the b-wave genesis could result from the time-integration of the OPs, possibly by a slow time-constant retinal membrane or pathway. We examined the latter hypothesis with normal and pathological ERGs using the discrete wavelet transform (DWT) approach.
This study was conducted on photopic ERGs obtained from normal subjects [N=85; flash intensity: -2.23 to 2.84 log cd.sec.m-2 in 22 steps of 0.2 log-unit; background: 30cd.m-2] and from (mostly retinitis pigmentosa) patients [N=118; flash intensity: 0.64 log cd.sec.m-2; background: 30 cd.m-2; monitoring: 1 to 10 visits over 5 to 25 years]. The DWT was used to quantify the contribution of the OPs [%OP=local energy (i.e. from 10 to 50 ms after flash onset) between 80-160Hz divided by the total local energy between 20-160Hz X100]. The mean b-wave amplitude of all the ERGs (all flash intensities) was also calculated and compared to the mean %OP.
%OP is stimulus-independent with a mean (±SD) value (all normal ERGs considered) of 35±3% [coefficient of variation (CV) <10%] compared to a CV >45% for the mean b-wave amplitude (60.09±27.21µV). Pathological ERGs had a mean %OP of 36±11% at initial visit, a value not significantly different from normal (p>0.05), but yielding a significantly larger than normal CV (CV=31%). In follow-up ERGs (≥3 visits; N=60), most patients (64%) showed a gradual increase in the %OP value, 23% a decrease and 13% showed no change in their %OP value with time.
Our study demonstrated that, in normal ERGs, the %OP value is relatively constant, not stimulus-dependent and consequently not influenced by the absolute amplitude of the ERG b-wave. In contrast, for a comparable range of ERG b-wave amplitudes (49.21±32.05µV), the %OP values measured in pathological ERGs vary significantly more (initial visit and follow-up measures), suggesting that the retinal event (? time constant of integrating retinal mechanism) thus quantified could be used to possibly detect retinal abnormalities at an earlier stage than what can be achieved using b-wave amplitude measurements, thus offering a new approach to pathological ERG categorization. Funded by FFB and Réseau-Vision.
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