Evaluating Outer Segment Length as A Surrogate Measure of Peak Foveal Cone Density

Authors

Melissa A. Wilk, Medical College of Wisconsin
Brandon M. Wilk, Medical College of Wisconsin
Christopher S. Langlo, Medical College of Wisconsin
Robert F. Cooper, Marquette University
Joseph Carroll, Marquette University

Document Type

Article

Language

eng

Publication Date

1-2017

Publisher

Elsevier

Source Publication

Vision Research

Source ISSN

0042-6989

Original Item ID

DOI: 10.1016/j.visres.2016.10.012

Abstract

Adaptive optics (AO) imaging tools enable direct visualization of the cone photoreceptor mosaic, which facilitates quantitative measurements such as cone density. However, in many individuals, low image quality or excessive eye movements precludes making such measures. As foveal cone specialization is associated with both increased density and outer segment (OS) elongation, we sought to examine whether OS length could be used as a surrogate measure of foveal cone density. The retinas of 43 subjects (23 normal and 20 albinism; aged 6–67 years) were examined. Peak foveal cone density was measured using confocal adaptive optics scanning light ophthalmoscopy (AOSLO), and OS length was measured using optical coherence tomography (OCT) and longitudinal reflectivity profile-based approach. Peak cone density ranged from 29,200 to 214,000 cones/mm²(111,700 ± 46,300 cones/mm²); OS length ranged from 26.3 to 54.5 μm (40.5 ± 7.7 μm). Density was significantly correlated with OS length in albinism (p < 0.0001), but not normals (p = 0.99). A cubic model of density as a function of OS length was created based on histology and optimized to fit the albinism data. The model includes triangular cone packing, a cylindrical OS with a fixed volume of 136.6 μm³, and a ratio of OS to inner segment width that increased linearly with increasing OS length (R² = 0.72). Normal subjects showed no apparent relationship between cone density and OS length. In the absence of adequate AOSLO imagery, OS length may be used to estimate cone density in patients with albinism. Whether this relationship exists in other patient populations with foveal hypoplasia (e.g., premature birth, aniridia, isolated foveal hypoplasia) remains to be seen.

Comments

Accepted version. Vision Research, Vol. 130 (January 2017): 57-66. DOI. © 2016 Elsevier Ltd. Used with permission.

Recommended Citation

Wilk, Melissa A.; Wilk, Brandon M.; Langlo, Christopher S.; Cooper, Robert F.; and Carroll, Joseph, "Evaluating Outer Segment Length as A Surrogate Measure of Peak Foveal Cone Density" (2017). Biomedical Engineering Faculty Research and Publications. 446.
https://epublications.marquette.edu/bioengin_fac/446