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Oliver J Flynn, Catherine A Cukras, Laryssa Huryn, Brett Jeffrey; Scotopic shape discrimination in AMD patients and healthy volunteers. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1208.
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Patients with intermediate and advanced age-related macular degeneration (AMD) show functional deficits in tests of shape discrimination performed under photopic conditions. We have developed a new scotopic shape discrimination task to measure rod function with the goal of detecting deficits not captured by other tests. We investigate the performance on this test in patients with intermediate AMD and healthy volunteers (HV) and also explore the effects of age on task performance.
Using radial frequency (RF) pattern arcs, we tested scotopic shape discrimination at 4° and 8° superior and inferior to the fovea in 7 patients with AMD—4 with large drusen (125 µm) without reticular pseudodrusen (mean age 75 yr.) and 3 with reticular pseudodrusen (mean age 70 yr.)—and in 21 HVs: 8 young (< 30 yr., mean = 22), 6 middle-aged (30-50 yr., mean = 39), and 7 older (> 50 yr., mean = 62). Participants were tested in one eye after 30 minutes of dark adaptation. A Medmont Dark Adapted Chromatic perimeter was used to measure scotopic sensitivity in AMD patients.
All AMD patients had dark-adapted scotopic sensitivity in the age-matched normal range. On average, eyes with AMD had significantly elevated discrimination thresholds compared to all HV groups (P < 0.0001). Compared with the oldest HV group, the AMD group had significantly elevated thresholds at 4° inferior retina (P = 0.009). Among all the HVs, there was a significant effect of age (P = 0.0004). However, the effect of age on discrimination thresholds was small compared with the large effect of AMD.
Our test results indicate a loss of rod-mediated resolution in eyes with AMD, perhaps due to dysfunctional or missing rod photoreceptor cells, that is not captured by a scotopic light sensitivity measure. We found a decrease in rod function, as measured by scotopic shape discrimination, in the central macula (4°) of AMD patients that was not observed in healthy volunteers. This data reinforces the findings of abnormal rod function in this parafoveal location in AMD and suggests that scotopic shape discrimination may be a sensitive measure of rod dysfunction in AMD, as a large area of rods is used to complete the task.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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