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J Jason McAnany, Jason C Park, Frederick T Collison, Gerald A Fishman; Full-field measures of visual function in X-linked retinoschisis: comparison of ERGs, luminance thresholds, and pupil responses. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4279.
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© ARVO (1962-2015); The Authors (2016-present)
X-linked retinoschisis (XLRS) is typically characterized functionally by reduced full-field dark-adapted electroretinogram (ERG) b-wave amplitude, but focal dark-adapted luminance thresholds are generally normal or minimally elevated. To investigate this apparent discrepancy, visual function was assessed in XLRS patients using three full-field measures: ERG, luminance threshold, and pupil size.
Dark-adapted ERGs and pupillary light reflexes (PLR: percentage pupil constriction due to light stimulation) were recorded from 5 XLRS patients (19 to 40 years) and 5 normally-sighted subjects (27 to 39 years). ERGs and PLRs were obtained for a range of flash luminances (ERG: -3 to 1 log cd s m-2; PLR: -3 to 2.6 log cd m-2) and these data were fit with Naka-Rushton functions to derive Rmax (maximum saturated response) and S (semi-saturation intensity; a sensitivity measure). PLR measurements were obtained with both 465 nm and 642 nm stimuli. Full-field dark-adapted luminance thresholds were also measured psychophysically at these wavelengths.
Analysis of variance (ANOVA) indicated significant reductions in dark-adapted b-wave amplitude for the XLRS patients compared to the controls for all flash luminances (p < 0.05). Naka-Rushton fits indicated that the patients had Rmax reductions that ranged from 0.05 to 0.74 log units and increased S (sensitivity loss) that ranged from 0.45 to 1.6 log units. ANOVA also indicated that the dark-adapted, short-wavelength PLR was significantly reduced in the patients for low luminance flashes (-3 to 1 log cd m-2; p < 0.05) but not for high luminance flashes (2.0 and 2.6 log cd m-2; p > 0.05). Long-wavelength PLRs were significantly reduced for the patients at all flash luminances (p < 0.05). For both wavelengths, there were minimal reductions in pupil Rmax (less than 0.11 log units) and substantial increases in S (0.65 to 2.13 log units). Luminance thresholds were within the range of normal for all patients; mean patient and control threshold did not differ significantly (p > 0.08).
The results highlight the somewhat paradoxical finding that the presumed bipolar cell deficit that occurs early in the visual pathway, indicated by b-wave abnormalities, does not significantly affect psychophysical luminance threshold or maximum pupil response, but does significantly reduce sensitivity within the pupil pathway.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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