A multipurpose SS-OCT engine – from axial eye length measurements to 4D OCT

Abstract

Purpose : The rigidity and low A-scan rate of spectral-domain optical coherence tomography (SD-OCT) is prohibiting a manifold use of OCT during ophthalmic surgery. We present a versatile swept-source OCT (SS-OCT) engine, addressing a multitude of use cases, from axial eye length measurements to live volumetric visualizations at MHz A-scan rates.

Methods : We developed a flexible SS-OCT engine and an add-on module to couple its sample arm to an ophthalmic surgical microscope. The engine includes a 1060nm tunable MEMS-VCSEL whose sweep repetition rate can be alternated between 100kHz, 400kHz or 1MHz. To increase the effective A-scan rate on cost of axial resolution, we scanned at twice the speed and mathematically divided each sweep into two halves. The 100kHz A-scan mode was used for high resolution B-scan and axial eye length measurements with an axial resolution of 6.3μm and an imaging depth of 29mm in tissue. For 4D live imaging, effective A-scan rates of 800kHz and 2MHz allowed us to realize fields of view (FOVs) of 3.1-15.7mm with imaging depths of 4.3-10.5mm and an axial resolution of 12.6μm. We imaged anterior segment and retina mimicking phantoms, as well as ex vivo porcine eyes. All data was processed and rendered live.

Results : Using the same instrument, we acquired full eye scans, anterior and posterior segment B-scans, as well as 4D-OCT scans with volume rates of up to 17vol/s. Fig.1 shows an ocular biometry scan of a test eye captured at an A-scan rate of 100kHz. Each B-scan consisted of 1024 A-scans. Sampling such enormous depths of 29mm in real-time allows for ocular distance measurements or solid state z-tracking. In Fig.2A-H an image sequence of a 17vol/s live rendered volume series can be seen. It visualizes an incision of a porcine cornea displayed at different viewing angles and zooms. An A-scan rate of 1MHz and axial resolution of 6.3μm resulted in a FOV of 3.1mm. To further enhance depth perception, depth is color-encoded from red (top) to blue (bottom) and the z-direction is indicated by an arrow.

Conclusions : We demonstrated SS-OCT’s potential to address multiple ophthalmic imaging applications with a single device. 4D OCT can be used for enhancing depth perception and visualizing sub-surface structures during surgery, while imaging at lower rates enables full eye OCT for high resolution B-scan imaging and biometry scans.

This is a 2021 ARVO Annual Meeting abstract.

 

Biometry scan of a phantom.

 

Volume series showing an incision of a porcine cornea.