Inter-individual biological variability of retinal layer thickness on optical coherence tomography scans.

PURPOSE: To identify the retinal layer with the lowest inter-individual variability in thickness, as a candidate anatomical reference for morphometric assessments in optical coherence tomography (OCT). METHODS: OCT images of 100 healthy eyes from 100 cases were captured using spectral domain-OCT. Six-millimeter horizontal scans bisecting the foveola were analyzed to determine the thicknesses of the ellipsoid zone, photoreceptor outer segment, interdigitation zone, retinal pigment epithelium/Bruch's membrane complex, external limiting membrane (ELM), myoid zone, and total retinal thickness, 500 µm from the foveal center on the temporal (T500) and nasal(N500) sides. The thickness of the foveal center and the thickest temporal and nasal retinal sections were measured both manually and with automated software, and the two methods were compared. Statistical analysis determined the anatomical parameter with the lowest coefficient of variation. RESULTS: Manual and automated thickness measurements of the foveal center and the thickest nasal and temporal segments yielded similar coefficient of variation values (manual: 9.5, 4.8, 4.8%; automated: 8.8, 4.8, 4.7%, respectively). Intraclass correlation coefficients between manual and automated measurements were excellent (0.975, 0.958, 0.966; p < 0.001). The coefficient of variation was higher in older subjects, particularly at the central fovea (manual: 10.9%, automated: 9.9% for individuals  > 65 years versus manual: 8.2%, automated: 7.8% for individuals  < 65 years), likely reflecting greater inter-individual biological variability in this age group. CONCLUSIONS: The thickest nasal and temporal parafoveal retinal sections exhibit the lowest inter-individual variability in thickness and represent candidate anatomical reference points for morphometric assessments on OCT.