Repeatability of cone photoreceptor metrics with a commercial adaptive optics scanning laser ophthalmoscopy (Mona II) in healthy adults

PURPOSE: To evaluate the repeatability of the adaptive optics scanning laser ophthalmoscopy (AO-SLO) system (Mona II) in measuring cone photoreceptor parameters and compare repeatability differences in different retinal regions. METHODS: A total of 126 healthy adults aged between 18 and 36 years with cycloplegic spherical equivalent refraction ≤+0.50 D and >-6.00 D were enrolled. Retinal images were captured at the macular fovea centre (0°, 0°), the temporal, nasal, superior and inferior regions at 1.5° and 3.0° eccentricity. At each region, multiple 2.4°×2.4° images were sequentially captured with 0.9°×2.4° overlap between adjacent regions, covering the detection area within 4.2° centred on the fovea. Three images with clear cone photoreceptors and image quality scores of 0.8 or above were selected from each region for analysis. RESULTS: All parameters of the cone photoreceptors demonstrated excellent repeatability, with intraclass correlation coefficient (ICC) ranging from 0.967 to 0.994. The cone density exhibited good repeatability, with the fovea and the nasal region at 1.5° eccentricity showing the highest ICC (0.992). For the cone spacing, regularity and dispersion also demonstrated high repeatability across all regions (all ICC >0.90). CONCLUSIONS: The Mona II AO-SLO system showed high repeatability in measuring parameters of cone photoreceptors in healthy adults, with consistent performance across retinal area within a 4.2° range. TRIAL REGISTRATION NUMBER: ChiCTR2500114249.