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Lea D Bennett, Richard G Weleber, Travis B Smith, Martin Klein, David G Birch; Volumetric assessment of scotopic visual field sensitivity in retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3250. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Static perimetry evaluates local luminance sensitivity and provides global indices, (mean sensitivity, mean deviation) as simplified metrics of a patient’s field of vision. Recently, Weleber, et al., 2015, applied topographic hill of vision modeling and volumetric indices to quantify magnitude and extent of photopic visual field sensitivity in patients with retinitis pigmentosa (RP). We retrospectively applied this method to scotopic full-field sensitivities to determine if volumetric indices enhanced interpretation of rod function in patients with RP.
Normal controls (n=7) and 63 consecutive patients diagnosed with RP with visual acuity >20/400 and kinetic visual field >10°, had one eye dilated and dark-adapted for 45 minutes. Sensitivity to a 505nm size V stimulus was tested with a 144°, 120-loci grid (solid angle 2.797 steradian, sr) with a dark-adapted chromatic perimeter (Medmont International Pty Ltd; Victoria, Australia). Field volumes were calculated with Visual Field Modeling and Analysis software (Weleber et al. 2015). Responses to scotopic ISCEV standard ffERG flashes were analyzed. Relationships were evaluated with Pearson’s correlation coefficient (r) and least squares regression.
The mean total scotopic visual field volume, VTOT, in dB-sr, for normal controls and patients with RP was 146.7±9 SD (range 135-159) and 44±34 SD (range 0-122), respectively. Of the 63 patients, 54(86%) had rod-mediated sensitivity in at least 3 field locations. FfERG responses to 0.01 and 3.0cd.s/m2 flashes were measurable from 32(51%) and 50(79%) of patients, respectively. The ffERG response to 0.01cd.s/m2 increased 1 log unit for every 42dB-sr increase in total field volume (r=0.6574, p<0.0001). Responses to the 3.0cd.s/m2 flash increased 1 log unit for every 49dB-sr increase in total field volume in patients with RP (r=0.7558, p<0.0001).
Rod-mediated vision was detected with scotopic perimetry in a higher percentage of patients than with ffERG. Volumetric indices broadened interpretation of rod function in patients with RP by providing a topographic model of the scotopic field of vision and by extracting the depth and magnitude of both rod-mediated function and scotomatous regions in the peripheral visual field. Scotopic perimetry will be beneficial for targeted treatment and as an index for the scope of rod impairment in patients with retinal diseases affecting rod photoreceptors.
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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