Low-cost swept-source optical coherence tomography and angiography

Abstract

Purpose : To demonstrate SS-OCT and OCTA with a low-cost single-mode vertical cavity surface emitting laser (VCSEL) for anterior and posterior eye imaging.

Methods : The central element of the proposed low-cost SSOCT system is a single mode VCSEL source operating at 850nm center wavelength, used extensively in cell phones and for LIDAR. The wavelength of such laser can be adjusted through thermal tuning by modifying the injection current's amplitude. Previously, long range imaging of the anterior eye segment down to the retina at 2kHz has been demonstrated. In the present work, we optimized the VCSEL tuning for comprehensive volumetric OCT and OCTA of the anterior and posterior eye. Optimal tuning characteristics to perform 3D OCT imaging have been found for 50kHz A-scan rate with an axial resolution of 24µm in tissue. The high A-scan rate allowed further to perform OCT angiography at the fundus as well as of scleral vessels.

Results : By optimizing the thermal tuning parameters at 50kHz a full-width-at-half-maximum spectral range of 10nm was achieved. The source exhibited high phase stability, thus no reference interferometer for sweep-linearization was needed. Applying a supervised deep learning-based noise reduction algorithm using a U-Net with averaged images as targets, the image quality could be further enhanced (Fig. 1 (b)). Segmentation of the 3D images at the retina provided thickness maps (from ILM to RPE) with a resolution of 20µm (Fig. 1 (c)). 3D anterior segment scans permit assessing corneal shape and thickness, as well as anterior chamber angle (Fig. 1(a)). OCTA results are shown revealing scleral as well as retinal vasculature (Fig. 1 (d)). Due to the lower axial resolution the visibility of smaller capillary vessels is reduced.

Conclusions : Although the resolution is significantly lower compared to state-of-the-art SS-OCT devices, the low-cost system provides clinically relevant information. In combination with automated image analysis algorithms, such system could in the future serve for example as screening tool for myopia or for monitoring diabetes or age-related-macula degeneration patients in a home or general remote care setting.

This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.

 

Figure 1: (a) Anterior segment tomogram and 3D rendering; (b) single retinal B-scan after convolutional-neural-network denoising; (c) retinal thickness map with ETDRS grid centered at the fovea; (d) OCT angiography at the optic nerve head;