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Anna A. Polunina, Sophie A. Kramer, Margarita G. Todorova, Andreas Schötzau, Anja M. Palmowski-Wolfe; Optimizing Filter Setting In The 2 Global Flash Multifocal ERG In POAG. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5698.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, filtering a special 2 global flash mfERG in POAG patients showed significant changes in the central 4° at 100-300Hz, 1-100Hz and 1-300Hz but not at 1-10Hz when compared to controls. This would suggest a filter setting of 10-300Hz to detect glaucomatous damage. Here we analyze, if this is indeed the case by examining the central response average in the same cohort of subjects.
A 2 global flash mfERG (VERIS 6.06TM, FMSIII) was recorded in 20 healthy subjects and 22 POAG patients with a bandpass filter (BPF) of 1-300Hz (F1) (103 Hexagons, M-sequence stimulus: LMax 100cd/m^2, Lmin <1cd/m^2, global flash: 200cd/m^2). The recorded data was filtered offline (VERIS 6.06). Root mean square was calculated. Three response epochs were analyzed: the response to the focal flash, at 15-45ms (DC) and the following two response components induced by the effects of the preceding focal flash on the response to the global flashes at 45-75ms (IC1) and at 75-105ms (IC2). The BPF setting 10-300Hz (F2) was compared to F1. Statistical analysis was performed using linear mixed effects models in the statistical package R version 12.1.
With F2 the DC in POAG differed more (p=0.0002) from normal than with F1 (p=0.0017). For IC1 the stronger difference between POAG and control was found with F1 (p<0.00001) rather then F2 (p=0.0001). IC2 also showed a stronger difference with F1 (p<0.00001) than F2 (p=0.0119).
A filter setting of 1-300Hz appears more sensitive to detect glaucomatous damage: Using a lower high pass filter (HPF) results in larger amplitudes (Lachapelle et al. 1994) which may be especially important in the small induced components that show glaucomatous damage most sensitively. Glaucoma did not differ from normal at 1-10Hz. Taken with the present results this suggests that a component at 10Hz may be notably affected in glaucoma. Interestingly, the DC seemed more abnormal with F2. Keating et al (1997, 2000) found a slight reduction in amplitude in the normal ERG when the HPF was increased to 10Hz. In the negative ERG this resulted in dramatic changes, such as an artificial positive component. Thus, increasing the HPF from 1Hz to 10Hz may affect a pathologic DC of the mfERGs in glaucoma and controls differently and thus artificially increase the difference between these responses.
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