High speed, long range, deep penetration swept source OCT for structural and angiographic imaging of the anterior eye

Abstract

This study reports the development of prototype swept-source optical coherence tomography (SS-OCT) technology for imaging the anterior eye. Advances in vertical-cavity surface-emitting laser (VCSEL) light sources, signal processing, optics and mechanical designs, enable a unique combination of high speed, long range, and deep penetration that addresses the challenges of anterior eye imaging. We demonstrate SS-OCT with a 325 kHz A-scan rate, 12.2 µm axial resolution (in air), and 15.5 mm depth range (in air) at 1310 nm wavelength. The ultrahigh 325 kHz A-scan rate not only facilitates biometry measurements by minimizing acquisition time and thus reducing motion, but also enables volumetric OCT for comprehensive structural analysis and OCT angiography (OCTA) for visualizing vasculature. The 15.5 mm (~ 11.6 mm in tissue) depth range spans all optical surfaces from the anterior cornea to the posterior lens capsule. The 1310 nm wavelength range enables structural OCT and OCTA deep in the sclera and through the iris. Achieving high speed and long range requires linearizing the VCSEL wavenumber sweep to efficiently utilize analog-to-digital conversion bandwidth. Dual channel recording of the OCT and calibration interferometer fringe signals, as well as sweep to sweep wavenumber compensation, is used to achieve invariant 12.2 µm (~ 9.1 µm in tissue) axial resolution and optimum point spread function throughout the depth range. Dynamic focusing using a tunable liquid lens extends the effective depth of field while preserving the lateral resolution. Improved optical and mechanical design, including parallax “split view” iris cameras and stable, ergonomic patient interface, facilitates accurate instrument positioning, reduces patient motion, and leads to improved imaging data yield and measurement accuracy. We present structural and angiographic OCT images of the anterior eye, demonstrating the unique imaging capabilities using representative scanning protocols which may be relevant to future research and clinical applications.

Electronic frequency shifting enables long, variable working distance optical coherence tomography

“…Although an Insight laser with a high degree of sweep linearization is applied here, other laser sources with a linearized sweep may also achieve extended ranging through our approach. For instance, a high degree of sweep linearization has been demonstrated using MEMS-VCSEL sources [ 9 , 32 , 33 ]. Although the degree of linearization is lower relative to the Insight laser, EFS-OCT may provide an extended depth range on the centimeter-scale using these sources as well.…”

Optical Coherence Tomography (OCT): A Brief Look at the Uses and Technological Evolution of Ophthalmology

“…6. Scan Speeds 400 A-scans per second [11] 20,000-52,000 A-scans per second [11] 100,000-236,000 A-scans per second [11,12]…”

The Latest Updates in Swept-Source Optical Coherence Tomography Angiography

“…The 3D imaging of the anterior segment may greatly improve ophthalmic imaging diagnosis for conditions such as intraocular lens implantation ( Figure 10 ) and anterior chamber space-occupying lesions. Anterior 3D-OCT is helpful in enabling precise customization in refractive surgeries, cataract intraocular lens implantation, and assessing the anterior angle and aqueous outflow for glaucoma diagnosis and monitoring [ 6 ].…”