Discernibility of the Interdigitation Zone (IZ), a Potential Optical Coherence Tomography (OCT) Biomarker for Visual Dysfunction in Aging

Abstract

Purpose

Photoreceptor (PR) outer segments, retinal pigment epithelium apical processes, and inter-PR matrix contribute to the interdigitation zone (IZ) of optical coherence tomography (OCT). We hypothesize that this interface degrades over adulthood, in concert with a delay of rod mediated dark adaptation (RMDA). To explore this idea, we determined IZ discernibility and RMDA in younger and older adults.

Methods

For this cross-sectional study, eyes of 20 young (20–30 years) and 40 older (≥60 years) participants with normal maculas according to the AREDS 9-step grading system underwent OCT imaging and RMDA testing at 5° superior to the fovea. Custom FIJI plugins enabled analysis for IZ discernibility at 9 eccentricities in 0.5 mm steps on one single horizontal B-scan through the fovea. Locations with discernible IZ met two criteria: visibility on B-scans and a distinct peak on a longitudinal reflectivity profile. The frequency of sites meeting both criteria was compared between both age groups and correlated with rod intercept time (RIT).

Results

The median number of locations with discernible IZ was significantly higher (foveal, 4 vs. 0, p = 0.0099; extra-foveal 6 vs. 0, p < 0.001) in eyes of young (26 ± 3 years) compared to older (73 ± 5 years) participants. For the combined young and older sample, the higher frequency of discernible IZ was correlated with shorter RIT (faster dark adaptation) (r_s = –0.56, p < 0.0001). This association was significant within young eyes (r_s = –0.54; p = 0.0134) and not within older eyes (r_s = –0.29, p = 0.706).

Conclusions

Results suggest that the interface between outer segments and apical processes degrades in normal aging, potentially contributing to delayed rod-mediated dark adaptation. More research is needed to verify an age-related association between IZ discernibility and rod-mediated dark adaptation. If confirmed in a large sample, IZ discernibility might prove to be a valuable biomarker and predictor for visual function in aging.

Keywords:

• Aging
• age-related macular degeneration
• structure-function correlation
• optical coherence tomography
• interdigitation zone
• rod-mediated dark adaptation

Disclosure statement

CO is an inventor on the device used to measure dark adaptation in this study. She consults for Johnson & Johnson Vision (outside this work). CAC receives research funds from Genentech/Hoffman LaRoche and Regeneron and consults for Apellis, Astellas, Boehringer Ingelheim, Character Biosciences, and Osanni (outside this project). No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Institutes of Health [R01EY029595 (CO and CAC), R01EY027948 (CAC), and P30EY03039 (CO)]; Dorsett Davis Discovery Fund; Alfreda J. Schueler Trust (CO); Dr. Werner Jackstädt-foundation (AB); Unrestricted funds to the Department of Ophthalmology and Visual Sciences (UAB) from Research to Prevent Blindness, Inc., and EyeSight Foundation of Alabama.