Variations in image optical quality of the eye and the sampling limit of resolution of the cone mosaic with axial length in young adults

PURPOSE: To evaluate the variation in higher-order ocular wavefront aberrations and the Nyquist limit of resolution of the cone mosaic (N-c) in a population of young healthy subjects and the relation to axial length (AL). SETTING: Fondazione G.B. Bietti IRCCS, Rome, Italy. DESIGN: Case series. METHODS: An adaptive optics retinal camera prototype (rtx1) was used to image the cone mosaic. Cone density and N-c were calculated at fixed eccentricity between 260 mu m and 600 mu m from the foveal center. Ocular higher-order wavefront aberrations were measured using the OPD Scan II device. The coefficient of variation (CoV) was used to analyze the variation in optical and retinal parameters. The correlation of optical and retinal parameters with AL was performed using Pearson analysis. RESULTS: Twelve subjects (age 24 to 38 years; AL 22.61 to 26.63 mm) were evaluated. A high interindividual variation in the higher-order wavefront aberrations was found, ranging from 26% for corneal higher-order aberrations (HOAs) to 41% for intraocular HOAs. The CoV of cone density and N-c were 16% and 5%, respectively. The decline in cone density and N-c with AL was statistically significant at all retinal eccentricities (R-2 > 0.44, P<.001). CONCLUSIONS: Although there appeared to be random variation in the eye's optical wavefront aberration from subject to subject, the cone-packing density and N-c were highly correlated with AL. Although the eye's overall image optical quality in the emmetropic group and the myopic group was comparable, the spatial sampling of the cone mosaic decreased with increasing AL.