Macular cone photoreceptor density distribution in fellow eyes of young adults

Abstract

 

Purpose

 

Quantitative estimation of cone packing density distribution in fellow eyes of young subjects with good retinal health may provide a baseline for understanding age- or disease-related cone loss. We examine macular cone photoreceptor density differences in fellow eyes using adaptive optics scanning laser ophthalmoscopy (AOSLO).

 

Methods

 

Twenty subjects aged 19-29 years were enrolled. All subjects underwent assessment of best-corrected visual acuity and measurement of refractive error to ensure no participant had refractive errors worse than -3 D or fellow-eye refractive error difference greater than 0.25 D. The retinal magnification factor for each subject was calculated using the Liou and Brennan eye model with the corneal curvature, anterior chamber depth, and axial length of the eyes measured using an ocular biometer. AOSLO was performed to image the maculae. Cone density was assessed over the central 2400 µm x 2400 µm macula, and evaluated statistically with a mixed model approach. Each eye was divided into four quadrants: superior/nasal (SN), superior/temporal (ST), inferior/nasal (IN), and inferior/temporal (IT). Within each quadrant, the association between cone density and eccentricity was compared between fellow eyes. A three-way interaction term was included in models to examine whether the association between eyes and cone density by eccentricity varied by quadrant.

 

Results

 

The isodensity lines of macular cone density of fellow eyes have the same shapes (Fig.1). There was no difference in the association between eccentricity and cone density in fellow eyes for the quadrants SN (p=0.8503), ST (p=0.1551), IN (p=0.8609), and IT (p=0.6662). Associations did not vary between quadrants (p=0.6772). In all subjects, the maximum cone density difference [assessed by (D_OS-D_OD)/D_OD] at a single sample point was 23.6%, and the root-mean-square difference was 6.78%.

 

Conclusions

 

We have characterized the macular cone density distribution in fellow eyes including the fovea in 2 dimensions, and estimated the maximum and average cone density differences. Overall, macular cone distributions in fellow eyes are radially and bilaterally symmetric, but considerable difference may exist at single points. The range of differences is consistent with data previously reported by Lombardo et al. for the parafoveal horizontal meridian.

 

 

Figure 1. Macular cone density distribution in subject 84. Plots are centered on the fovea.

 

Keywords: 648 photoreceptors • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 688 retina