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K. Holopigian, J. M. Gallardo, W. Seiple, W. H. Swanson, R. E. Carr; Visual Field and Multifocal ERG Progression in Patients With Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6258.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with retinitis pigmentosa (RP) have eccentricity-dependent losses in visual function, and visual fields have been used to establish the progression rate in patients with RP. More recently, the multifocal ERG (mfERG) has been used to assess progression in RP (Nagy, et al, 2008, IOVS 49:4464). In the current study, we assessed eccentricity-dependent rates of change in visual fields and mfERGs for the same retinal locations in a group of patients with RP.
Humphrey threshold visual fields and mfERGs were measured for 39 patients with RP for follow-ups from 3 to 9 years. Monocular threshold visual field testing was done with a modified program of 103 points corresponding to our mfERG array. mfERG recordings were done with a VERIS system and a scaled array of 103 hexagons. Each hexagon was evaluated independently and values of relative amplitude and implicit time were obtained (Hood and Li, 1997, OSA 11:33).
The data were grouped into 3 rings: ring 1 (the fovea and hexagons to 5o), ring 2 (to 10o) and ring 3 (all remaining points to 25o). The data were averaged in linear units and log transforms were performed. For each patient and ring, data were plotted as a function of follow-up years and linear regression was used to derive the rate of change in dB/year. For the mfERG, data were only available for a subset of 27 patients for whom responses were recordable on ≥ 2 visits and for these patients, there were 49% fewer visits with measurable data for the mfERG than for the visual fields. For all measures, the median loss at the initial visit (intercept) varied significantly with eccentricity; for visual fields the initial loss was 2.6 dB for ring 1, 7.5 dB for ring 2 and 14.9 dB for ring 3. For amplitude, the initial loss was 6.0 dB, 8.8 dB and 10.4 dB for rings 1-3; for implicit time, the initial loss was 0.2 dB, 0.8 dB and 1.3 dB for rings 1-3. For visual fields only, progression (slope of the regression line) changed significantly with eccentricity (p = 0.018); the slopes were 0.03 dB/year, -0.09 dB/year and -0.40 dB/year. For amplitude, the slopes were 0.001 dB/year, -0.26 dB/year and -0.31 dB/year for rings 1-3; for implicit time they were 0.004 dB/year, 0.02 dB/year and 0.1 dB/year.
All measures showed differences in the amount of initial loss and some change in the rate of progression with eccentricity. However, the mfERG data were more difficult to record accurately and showed greater variability, making it more difficult to assess these changes. This may be due to differences in measurement scale ranges, as well as in the amount of loss at baseline.
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