Imaging the full eye with low-cost swept-source optical coherence tomography

Abstract

Purpose : To investigate the adequacy of a low-cost single-mode vertical cavity surface emitting laser (VCSEL) as the light source for full eye swept-source optical coherence tomography (SS-OCT).

Methods : The center wavelength of single-mode VCSELs can be tuned thermally by varying the amplitude of the injection current. Such a source with a center wavelength of 850 nm was used as low-cost swept-source for a Mach-Zehnder-based long-range SS-OCT system. Lateral scanning in the sample arm was achieved using a microelectromechanical system (MEMS) mirror. The system can be operated at A-scan rates of 2-50 kHz and achieves an axial resolution of about 35-50 µm in tissue. Due to the VCSEL’s long coherence length, the system supports an imaging depth of 5 cm with a roll-off of less than -3 dB at 2 kHz sweep repetition rate. This enables imaging of the full anterior segment while at the same time obtaining a signal from the retina, which can be used for axial eye length measurements. By adding an additional lens in the sample arm, we could further perform widefield imaging of the posterior segment.

Results : Our low-cost SS-OCT system achieved a sensitivity of 97 dB at 2kHz A-scan rate, with an optical power of 200 µW measured at the cornea. The system’s large imaging depth is demonstrated in Figure 1 (a-b), in the form of anterior segment B-scans of a healthy volunteer. These B-scans were acquired at A-scan rates of 25 kHz and 50 kHz, with 1200 A-scans per B-scan, and were averaged 20x. For the 50 kHz B-scan we observed a stronger sensitivity roll-off with depth. This comes as a consequence of the detector’s noise performance at higher detection frequencies. Figure 1c shows an example of a widefield posterior segment B-scan covering 9 mm on the retina. This scan was acquired at 25 kHz A-scan rate and 40x B-scan averaging was applied to improve signal-to-noise ratio and reduce speckle noise.

Conclusions : We presented a low-cost SS-OCT system for anterior as well as posterior segment imaging, using a tunable single mode VCSEL. Although the resolution and image quality are significantly lower compared to state-of-the-art SS-OCT devices, it has the potential to provide clinically relevant information. In combination with automated image analysis algorithms, such systems could serve as screening tools outside the traditional eye clinic or optometrist practices in the future.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.