Three-dimensional assessment of para- and perifoveal photoreceptor densities and the impact of meridians and age in healthy eyes with adaptive-optics optical coherence tomography (AO-OCT).

An adaptive optics optical coherence tomography (AO-OCT) system is used to assess sixty healthy eyes of thirty subjects (age 22 to 75) to evaluate how the outer retinal layers, foveal eccentricity and age effect the mean cone density. The cone mosaics of different retinal planes (the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST), and the full en-face plane (FEF)) at four main meridians (superior, nasal, inferior, temporal) and para- and perifoveal eccentricities (ecc 2.5° and 6.5°) were analyzed quantitatively. The mean overall cone density was 19,892/mm at ecc 2.5° and 13,323/mm at ecc 6.5°. A significant impact on cone density was found for eccentricity (up to 6,700/mm between ecc 2.5° and 6.5°), meridian (up to 3,700/mm between nasal and superior meridian) and layer (up to 1,400/mm between FEF and IS/OS). Age showed only a weak negative effect. These factors as well as inter-individual variability have to be taken into account when comparing cone density measurements between healthy and pathologically changed eyes, as their combined effect on density can easily exceed several thousand cones per mm even in parafoveal regions.