Abstract
Purpose :
Many inherited retinal degenerations (IRD) present with nyctalopia and peripheral vision loss. Despite this, spatial assessments of scotopic visual function are limited. Scotopic microperimetry combines scotopic two-colour (cyan and red stimuli) perimetry with fundus-controlled microperimetry. By analysing the cyan minus red stimuli sensitivity differences, it enables scotopic central retinal sensitivity mapping and spatial identification of photoreceptor dysfunction. Mesopic microperimetry has become a prominent outcome measure in IRD clinical trials. However, the use of scotopic microperimetry in IRDs is less well established, we sought to determine more about the usefulness of this test.
Methods :
Participants underwent 20 minutes dark adaptation before two-colour scotopic microperimetry, on one eye, using the Macular Integrity Assessment System (MAIA; CenterVue, Padova, Italy), 37-point, ultra-wide radial grid, with cyan and red stimuli, respectively. Five participants underwent repeat scotopic testing. The reliability indices and repeatability were analysed.
Results :
Thirteen participants with genetically confirmed IRD diagnoses (CHM = 10, USH2A =2 and RHO =1) and good visual acuity (mean VA 83 [SD±5] ETDRS letters) completed microperimetry. Three participants were excluded due to >20% fixation losses. The remaining 10 participants showed good fixation stability with a mean 95% bivariate contour ellipse fixation area of 1.57 (SD±1.71) and 2.56 (SD±3.62) degrees2 for cyan and red stimuli, respectively. Mean cyan sensitivity (dB) was 5.36 (SD±6.9), mean red sensitivity was 8.41 (SD±7.7), cyan minus red sensitivity was -3.19 (SD±4.9). The individual test point repeatability for cyan stimuli was ±6.42dB, ±4.67dB for red stimuli and ±7.57dB for cyan minus red. Cyan minus red sensitivity plots showed both choroideremia and USH2A-associated retinitis pigmentosa (RP) participants had mixed rod/cone photoreceptor dysfunction. Whereas the Rho-associated RP participant showed diffuse rod specific dysfunction.
Conclusions :
Scotopic microperimetry appears a reliable and repeatable marker of scotopic central macular sensitivity. However, to more accurately model the patterns of photoreceptor dysfunction in different IRDs, it may be necessary to consider specific pointwise test-retest variability values when categorising between rod versus cone retinal dysfunction.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.