Evaluation of different OCT systems in quantitative imaging of Schlemm's Canal in human

Abstract

Purpose : The morphology of SC is believed to be closely related to glaucoma and accurate assessment on the dimension of Schlemm’s Canal (SC) is vital. Optical coherence tomography (OCT) enables high-resolution, three-dimensional (3D) imaging of SC in living humans. This study quantitatively compares the performance of three commercial OCT systems in SC imaging and analyzes the impact factors that may affect the image quality as well as the morphological analysis of SC therefrom. Our study provides a guideline to choose an optimized OCT system for better visualization of SC.

Methods : Ten healthy subjects were imaged using three OCT machines: ZEISS Cirrus 5000 (840nm, spectral-domain (SD)-OCT), ZEISS Plex Elite 9000 (1060nm, swept-source (SS)-OCT) and Tomey Casia (1310nm, SS-OCT). For each subject, both eyes underwent two cubic scans by each machine, one on the nasal quadrant and the other temporal. The B-scan showing the largest SC was chosen and processed to obtain SC dimensional metrics. The SC contrast was investigated by quantitative comparison. Four morphological metrics, including the cross-sectional area (CSA), the perimeter, the longest, and shortest diameters of SC, were extracted via manual segmentation. The difference between the three OCT systems were analyzed.

Results : The CSAs were significantly different between different machines (Cirrus - Casia: Δ=1763.89µm², p＜0.001; Plex - Casia: Δ=1026.21µm², p＜0.001; Cirrus - Plex: Δ=737.68µm², p=0.003), as well as the longest diameters (Cirrus - Casia: Δ=56.50µm, p＜0.001; Plex - Casia: Δ=39.29µm, p＜0.001; Cirrus - Plex: Δ=17.21µm, p=0.031). The SC perimeter measured from Casia was significantly different compared to that from Cirrus or Plex (Cirrus – Casia: Δ=100.90µm, p＜0.001; Plex – Casia: Δ=39.29µm, p＜0.001). The shortest diameter measured from Cirrus and Casia was significantly different (Δ=-3.9µm, p=0.039). The Michelson contrast was seen highest in Cirrus (0.63±0.05), mediocre in Plex (0.57±0.06), while lowest in Casia (0.40±0.07). Based on visual assessment, the 1060nm system showed a good balance in angle delineation and SC visualization. Conversely, the 840nm system displayed good performance in SC visualization while the 1310nm system excelled in angle delineation.

Conclusions : The wavelength and resolution of the anterior segment OCT system may affect the visualization as well as the quantitative assessment of SC morphology.

This is a 2021 ARVO Annual Meeting abstract.