High-Speed, Long-Range Swept-Source Optical Coherence Tomography for the Anterior Segment of the Eye

Abstract

Purpose : The anterior segment (AS) of the eye is of interest in multiple diseases and procedures, including glaucoma, ocular surface inflammation, and refractive / cataract surgeries. Visualizing the anterior eye using optical coherence tomography (OCT) has unique challenges, and AS OCT technology is less developed than retinal imaging. We developed next generation swept-source OCT (SS-OCT) technology to enable high-speed and long-range AS structural and angiographic imaging in clinical settings.

Methods : We designed a SS-OCT prototype instrument using wavelength-tunable, vertical-cavity surface-emitting laser (VCSEL) with linearized frequency sweep. The OCT wavelength centers at 1310 nm with a 105 nm bandwidth. The A-scan rate is 325 kHz, and the OCT fringes are digitized at 2 giga samples per second to achieve long-range imaging of the entire anterior segment. An electrically tunable lens adjusts the focal plane to extend the effective image range. A “split-view” iris monitor, which uses two cameras looking at the eye at symmetric oblique angles, ensures both transverse and axial positioning accuracy. Graphic processing unit (GPU) was used to perform sweep-by-sweep calibration to achieve high measurement accuracy, as well as to correct laser instability and provide near real-time OCT reconstruction. This allows the operator to immediately visualize the acquired OCT volume, streamlining the clinical work flow and improving imaging yield.

Results : The SS-OCT prototype has an axial resolution of 12.2 µm, and an imaging range of ~16 mm in air. The axial resolution is invariant over the range, which is important for biometry. The sensitivity is 105 dB (5 mW incident) with minimal sensitivity roll-off. We demonstrate wide field-of-view imaging and dynamic focusing of repeated B-scans. We also performed OCT angiography (OCTA). An example demonstrating elevated vessel density due to contact lens wear is shown.

Conclusions : The combination of high-speed, long-range, dynamic focusing, and high-performance OCT signal processing is a unique technical advance for AS imaging. These improvements promise to be a useful tool for investigating structural and vascular features of the anterior eye.

This is a 2021 Imaging in the Eye Conference abstract.

 

(A) Split-view iris monitor. (B-C) Wide field-of-view (25 mm) OCT scan. (D-F) Focal sweep within repeated OCT B-scans.

 

Slit lamp photo (A), OCT en face view (B), and depth-encoded OCTA (C) on the eye of a contact lens wearer.