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The effect of filtering on the two-global-flash mfERG: identifying the optimal range of frequency for detecting glaucomatous retinal dysfunction

Ledolter, Anna ; Kramer, Sophie ; Todorova, Margarita ; Schötzau, Andreas ; Palmowski-Wolfe, Anja

In: Documenta Ophthalmologica, 2013, vol. 126, no. 2, p. 117-123

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    Title
    • The effect of filtering on the two-global-flash mfERG: identifying the optimal range of frequency for detecting glaucomatous retinal dysfunction
    Author
    • Ledolter, Anna. Department of Ophthalmology, University of Basel, Mittlere Strasse 91, 4031, Basel, Switzerland
    • Kramer, Sophie. Department of Ophthalmology, University of Basel, Mittlere Strasse 91, 4031, Basel, Switzerland
    • Todorova, Margarita. Department of Ophthalmology, University of Basel, Mittlere Strasse 91, 4031, Basel, Switzerland
    • Schötzau, Andreas. Department of Ophthalmology, University of Basel, Mittlere Strasse 91, 4031, Basel, Switzerland
    • Palmowski-Wolfe, Anja. Department of Ophthalmology, University of Basel, Mittlere Strasse 91, 4031, Basel, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:313421
    Summary
    Purpose: To study the effects of filtering bandwidth on the two-global-flash multifocal electroretinogram (mfERG) responses in primary open-angle glaucoma (POAG) compared with control subjects. Methods: A two-global-flash mfERG (VERIS 6.06™, FMS III) was recorded in 20 healthy subjects and 22 POAG patients with a band-pass filter (BPF) of 1-300Hz (103 Hexagons, M-sequence stimulus: Lmax 100cd/m2, Lmin<1cd/m2, global flash: 200cd/m2). The root-mean-square average of the central 10° was calculated. Three response epochs were analysed: the response to the focal flash, at 15-45ms (DC), and the following two 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 following BPF settings were analysed: 1-300Hz, 3-300Hz, 10-300Hz, 100-300Hz, 200-300Hz, 1-10Hz, 1-100Hz and 1-200Hz. Results: Filtering at 1-300Hz showed significantly lower responses in POAG than in control subjects (p<0.001) for all epochs analysed. At 1-100Hz, this also held true even though the difference between the groups became smaller. At 1-10Hz, responses were extremely small and did not differ between POAG and control (p>0.5). This would suggest a filter setting of 10-300Hz for mfERG recordings in POAG. However, when a filter setting of 10-300Hz was compared to 1-300Hz, with a filter setting of 10-300Hz, the DC in POAG differed more (p<0.0001) from normal than with 1-300Hz (p=0.0002). For IC1 and IC2, the stronger difference between POAG and control was found with 1-300Hz (p<0.0001) rather than with 10-300Hz (p<0.0001 and p=0.0005, respectively). For the ‘oscillatory potentials' at 100-300Hz, POAG and control differed significantly in IC1 and IC2 (p<0.05), but not in DC (p=0.8). However, filtering at 200-300Hz did not show a difference between POAG and control (p>0.5). Thus, we applied a filter setting of 1-200Hz, which seemed to be most sensitive in detecting glaucomatous retinal dysfunction (p<0.0001). Conclusions: A filter setting of 1-200Hz appears most sensitive to detect glaucomatous damage if using a two-global-flash mfERG: using a band-pass filter a with lower low-frequency cut-off, containing the 10Hz component, may be especially important in the small induced components that show glaucomatous damage most sensitively. High frequencies of 100-300Hz also contain information that differentiates glaucoma from normal and thus should be included in the analysis