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

Andreas Berlin; Emily Matney; Skyler G Jones; Mark E Clark; Thomas A Swain; Gerald McGwin Jr; Richard M Martindale; Kenneth R Sloan; Cynthia Owsley; Christine A Curcio

doi:10.1080/02713683.2023.2240547

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

Curr Eye Res. 2023 Nov;48(11):1050-1056. doi: 10.1080/02713683.2023.2240547. Epub 2023 Aug 4.

Authors

Affiliations

¹ Department of Ophthalmology and Visual Sciences, Heersink School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.
² Department of Ophthalmology, University Hospital Würzburg, Würzburg, Germany.
³ Department of Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, AL, USA.

PMID: 37539829
PMCID: PMC10592305 (available on 2024-11-01)
DOI: 10.1080/02713683.2023.2240547

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; interdigitation zone; optical coherence tomography; rod-mediated dark adaptation; structure-function correlation.

Abstract

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