En Face Visualization of the Retinal Pigment Epithelium and Choroid in Chorioretinal Diseases using Swept-Source Optical Coherence Tomography

Abstract

 

Purpose

 

To investigate volumetric swept-source OCT (SS-OCT) at 1050nm for en face visualization of the retinal pigment epithelium (RPE) and choroid in retinal pathologies.

 

Methods

 

A SS-OCT prototype system operating at 100kHz axial scan rate with 6µm axial resolution at 1050nm for enhanced choroidal penetration was used. Orthogonal raster scans of the macula with 400x400 A-scans over a 6 x 6mm region were acquired. Software motion correction was used to register and merge the volumetric data and enhance the signal. The RPE was segmented using an intensity and gradient-based semi-automatic algorithm and en face images were extracted at different depths using the RPE/Bruch’s membrane as a reference layer. 12 healthy subjects and 26 patients presenting with clinical diagnoses of diabetic retinopathy (DR), age-related macular degeneration and central serous chorioretinopathy (CSCR) were imaged using approved IRB protocols from the New England Eye Center and Massachusetts Institute of Technology. Patients had standard ophthalmic clinical examination, including fundus photography, fluorescein angiography and in some cases, ICG angiography.

 

Results

 

38 eyes were included in the study. Manual and semi-automatic segmentation generated comparable visualization of changes in the RPE (fig 1). En face images are able to visualize the spotted appearance of the choroid at the level of choriocapillaris and tortuous vascular patterns in deeper choroidal layers. Findings in en face images of healthy eyes and patients with proliferative DR, geographic atrophy (GA) and CSCR were correlated to B-scans (fig 2).

 

Conclusions

 

SS-OCT at 1050nm with software motion correction provides comprehensive 3D images of the choroid, which enable the generation of high quality en face images. En face imaging is a reliable tool for visualizing different layers of the choroid in healthy and diseased eyes. Changes in the RPE and choroid could consistently be detected in both B-scans and en face images.

 

 

Fig 1: SS-OCT en face images of the RPE (thickness=20µm) using manual (left) and semi-automatic (right) segmentation (A) normal subject (B) PDR with neovascularization (C) GA (D) CSCR

 

 

Fig 2: Correlation of B-scans (left) und choroidal en face images (thickness=20 µm) extracted 40µm and 80 µm below the RPE (red line) (A) normal subject (B) PDR with neovascularization (C) GA (D) CSCR

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 549 image processing • 452 choroid