Age-Related Variations in the External Limiting Membrane and the Ellipsoid Zone

Abstract

Purpose : To evaluate sub-band visibility between the external limiting membrane (ELM) and ellipsoid zone (EZ) and changes associated with aging using high-resolution (HR) OCT.

Methods : In a post-hoc analysis of a prospective cross-sectional study, a total of 44 healthy eyes from 44 adults were imaged using an HR OCT prototype (2.7-µm axial resolution, 128 kHz A-scan rate). Six orthogonal raster scans of 500 x 500 A-scans over 6mmx6mm were acquired. Next, advanced volume fusion using spatiotemporal motion and illumination correction was performed to achieve subpixel accuracy in all 3 dimensions. The subjects were divided into three groups: young (21-40 y/o), middle (41-60 y/o), and older age (>=60 y/o). The OCT images were flattened to Bruch’s membrane and displayed in linear scale to highlight the sub-band between ELM and EZ. Three expert graders assessed foveal center B-scans to grade the sub-band visibility: 1- less distinct, 2- distinct, 3- unclear. The relative peak intensities at the sub-band were measured. The association of the sub-band with age group was investigated.

Results : Figure 1 shows representative OCT showing the sub-band, which has been attributed to the photoreceptor inner segment myoid zone. The compiled B-scan gradings across the measured foveal eccentricities (0.5mm, 1mm, 2mm) in young, middle, and older age groups were 1.2, 1.6, and 2.0, respectively. This showed statistically significant differences (p < 0.03) between the three age groups at all distance points. The relative A-scan intensity was positively correlated (r=Pearson’s correlation coefficient) with age at 0.5mm nasal [r=0.31 (p=0.04)], 1mm temporal [r=0.43 (p=0.003)], and 2mm temporal [r=0.48 (p=0.001)], suggesting increased visibility of the sub-band with aging. Furthermore, young and middle age groups showed statistically significant changes in visibility with eccentricity.

Conclusions : The HR OCT prototype, coupled with advanced motion correction and volume fusion, shows the presence of a sub-band, and its visibility changes with aging.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1. Representative axially stretched, flattened OCT with adjusted image display scale, highlighting (A) a discernible sub-band (yellow) below the ELM from a 64 y/o female subject and (B) less distinct sub-band from a 29 y/o female subject. The zoomed-in images provide a detailed view of the peak intensity (blue arrows) along the yellow line.