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P. Wynn, K. Holopigian, R.E. Carr, D.C. Hood; A Comparison of Multifocal and Full–field Photopic Electroretinograms in Patients with Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5098.
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Purpose: To better understand the relationship between multifocal and standard, full–field electroretinograms (ERG). Methods: 12 controls and 12 patients with retinitis pigmentosa (RP) were tested with multifocal (mf) and full–field (ff) ERGs and static perimetry. The patients had visual acuities of 20/30 or better. Full–field photopic, single flash (sf) and 30 Hz flicker (30Hz) responses were obtained with a Ganzfeld stimulator (Roland Instruments) as specified by the ISCEV standards. The mfERGs were recorded to local flashes (std–mf) using the typical fast VERIS protocol (EDI) and to local 30 Hz flicker (30Hz–mf) using the LED display of RETIscan (Roland Instruments). The multifocal displays were high contrast (light/dark) stimuli averaging 100 cd/m2. The mfERG stimuli consisted of 61 scaled hexagons within a field 45 degrees in diameter. Static automated perimetry (Humphrey Instruments) was performed using three tests, 30–2, 60–4 and a modified program corresponding to the mfERG display. The amplitudes of the mfERGs summed across the field were compared to each other (std–mf vs. 30Hz–mf) and to the full–field measures on log–log plots. On a log–log plot, a slope of 1.0 would indicate that the responses were a constant ratio of one another. The mf responses also were summed by annuli and compared to the field data. Results: The amplitudes of the two ff–ERGs showed good agreement (r = 0.93) and were fitted well to a line with a slope of 1.0. The comparison of the summed mf–ERG measures to each other, or to the ff–measures, showed poorer overall correlations (r = 0.70 to 0.85) and considerable deviation from a line with a slope of 1.0. For example, the data from four of the patients consistently deviated in the direction of relatively larger 30Hz–mf responses compared to std–mfERGs and relatively larger ff–ERGs (sf) responses as compared to std–mfERGs. These four patients had the largest full–field responses and showed large 30 Hz–mfERGs in regions of poor field sensitivity. Conclusions: Although the amplitudes of the ff– and mf–ERGs are correlated, the relationship between the two can be complex. Consideration of the extent and health of the visual fields, as well as possible contributions from stray light, can explain some, but not all, of the complexities. 1. Marmor & Zrenner (1999) Doc. Ophthal. 2. Hood et al (1998) Vis. Res.
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