Relationship between structured light perception and outer retinal layer thickness

Abstract

Purpose : Structured light (SL) with variable spatial polarization interacts with the birefringent properties of the Henle fibre layer (HFL) to produce entoptic images. We investigated the relationship between the size of SL entoptic images and the thickness of the outer retinal layers. Our long-term goal is to assess whether SL can be used to detect the early signs of age-related macular degeneration (AMD).

Methods : A coherent superposition of a planar right-circularly polarized state and a helical left-circularly polarized state (with orbital angular momentum (OAM) l=5,10,15 and 20) was used to generate psychophysical stimuli. A blue beam (λ=450 nm) was presented to 21 healthy participants for 0.5s per trial during which an azimuthally varying entoptic profile rotated clockwise or counterclockwise. A circular mask with a varying radius was placed at fixation, thus the task was performed at varying eccentricities. The threshold mask size was changed by a staircase method (71% accuracy for the estimation of mask size). Retinal optical coherence tomography (OCT) imaging was performed using a Topcon Maestro2, and the thickness of HFL and outer nuclear layer (ONL) was measured in the foveal (1 mm), parafoveal (1mm-3mm) and perifoveal (3mm-6mm) regions (Figure 1: A and B). Mask size thresholds for the different OAM states were averaged for each participant prior to analysis.

Results : Larger mask size thresholds (larger entoptic images) were associated with greater HLF and ONL thickness in the macula (Figure 1C) and in its separate internal regions (Table 1).

Conclusions : Entopic images generated by structured light extend further into peripheral vision when the HFL and ONL are thicker indicating an association between retinal structure and the entoptic effects of structured light.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure 1. A – segmentation of retinal OCT layers; B – measurement of HFL and ONL thickness (in μm) in the fovea (1mm), parafovea (inner ring, 3mm) and perifovea (outer ring, 6mm). C – Relationship between the thickness of HFL and ONL in the macula and threshold mask size (entoptic image size)

 

Table 1. Relationship between threshold mask size (entoptic image size) and thickness of Henle fibre (HFL) and outer nuclear layers (ONL)