Ultrahigh-Resolution Optical Coherence Tomography Investigation of Age-Related Changes in the Photoreceptors, Retinal Pigment Epithelium and Bruch’s Membrane

Abstract

Purpose : Aging is the biggest risk factor for age-related macular degeneration (AMD). Previous histological and ultrastructural studies have suggested that photoreceptors (PR), retinal pigment epithelium (RPE), and Bruch’s membrane (BM) undergo changes with aging and in AMD. A new high-speed, ultrahigh-resolution optical coherence tomography (UHR OCT) prototype instrument with depth tracking and software motion correction was used to investigate PR/RPE/BM alterations in normal aging and early AMD.

Methods : We developed a high-speed UHR OCT instrument with 2.7 µm axial resolution and 128 kHz A-scan rate. A galvanometer scanner actuates the OCT reference arm to match the retinal contour between B-scans, extending the effective imaging range. We developed examination protocols using multi-volume scan covering 6×6 mm² (500×500 A-scans) for software motion correction, and high-definition (HD) scan covering 9×6 mm² (1800×241 A-scans). Because the transverse resolution is ~20 µm, the HD scanning allows ensemble sampling of fine, sub-resolution features. We compared UHR OCT from healthy eyes in different age groups and early AMD eyes.

Results : To date 45 normal eyes from 25 subjects were imaged (mean age: 50±16.7 y.o.; range 25 – 72 y.o.). We also imaged a cohort of patients with different stages of AMD. UHR OCT revealed alterations in bands corresponding to the external limiting membrane (ELM), inner segment/outer segment junction or ellipsoid zone (IS/OS, EZ), cone/rod interdigitation zone or cone/rod outer segment tips (CIZ/RIZ, COST/ROST), RPE, and BM. These bands are sharp and distinctive in young healthy eyes; RPE and BM can usually be separately resolved. With aging, the outer retinal OCT bands become less defined axially; RPE and BM appear blurred and merge together. In early AMD eyes, these structural bands become less distinct, accompanied by occasional disruption of layered structures. A hypo-reflective gap between the RPE and BM is often observed in early AMD eyes.

Conclusions : UHR OCT promises to be a useful tool to investigate outer retina alterations in both normal and diseased eyes. This may provide better understanding of both normal aging and pathophysiological alterations of PR/RPE/BM, potentially identifying new markers for detecting and monitoring diseases such as AMD.

This is a 2020 Imaging in the Eye Conference abstract.

 

Representative UHR OCT HD B-scans.