Harnessing power of swept-source OCT

TAKE HOME MESSAGE: An anterior segment diagnostic imaging platform based on high-speed swept-source OCT is being developed by Heidelberg Engineering. It will provide biometry as well as corneal topography and tomography, while also enabling visualization of the anterior and posterior lens surfaces and assessment of the anterior chamber angle.

By Cheryl Guttman Krader; Reviewed by Christian Mardin, MD 

An anterior segment diagnostic imaging platform based on high-speed swept-source OCT is still under development, but being looked at with great interest by cataract and refractive surgeons because of the breadth and detail of the information it will provide.

The system from Heidelberg Engineering was previewed at the XXXIII ESCRS Congress in September, 2015 and can be seen at the Heidelberg booth in the technical exhibit hall at the AAO meeting in November, 2015. It will obtain anterior and posterior corneal topography and tomography, total corneal power, axial length, anterior chamber depth, and lens thickness. In addition, it enables visualization of the anterior and posterior lens surfaces along with assessment of the anterior chamber angle. Importantly, acquisition of all of these data and images is completed with the convenience of a single scan, and the information is provided to the examiner in a customizable printout.

Kester Nahen, PhD, Managing Director, Heidelberg Engineering, Heidelberg, Germany, told Ophthalmology Times, “The Cataract and Refractive Imaging Platform has been designed to carry out the most important examinations for the purposes of cataract surgery, refractive surgery, and angle assessment using a single device. Like other Heidelberg Engineering systems, the platform has a modular design, which allows configuration to the specific diagnostic workflow of the practice or clinic, and it is upgradable. In addition, it will seamlessly integrate with our platform that provides centralized management of diagnostic images (HEYEX PACS).”

Christian Mardin, MD, professor of ophthalmology, University of Erlangen-Nuremberg, Erlangen, Germany, has been one of the first clinicians to work with this new cataract and refractive imaging platform.  He told Ophthalmology Times, “The opportunity for acquisition of high-resolution anterior segment images simultaneously with anterior segment biometry using a single device brings a great benefit for increased efficiency because it reduces the duration of the diagnostic examination and improves workflow in the clinic. With this new system, patients no longer have to be moved from device to device and perhaps even from room to room.” 

Dr. Mardin added, “Furthermore, with one glance at a single report, the examiner can check the validity of all measurements by simultaneous presentation of OCT B-scans.”

Like spectral-domain OCT, swept-source OCT provides better resolution and faster acquisition speed than time-domain OCT technology. Thus, very dense scan patterns can be used to quantitatively analyze various structures, such as the anterior and posterior corneal surfaces.

However, for the anterior segment, swept-source OCT has advantages over spectral-domain, said Dr. Nahen. “Due to the almost constant sensitivity over depth of the signal, with swept-source OCT it is possible to visualize the region from the corneal surface to the posterior lens surface in a single scan. Secondly, because of the large dynamic range of the OCT signal, both high-scatter and low-scatter areas can be seen simultaneously; in other words, iris and lens can be clearly displayed in a single image.”

He also noted that the relatively long wavelength being used with the new imaging platform, 1300 nm, is ideal for imaging through scattering structures. “A shorter wavelength would not penetrate sclera as well and it would be harder to visualize and assess the configuration of the anterior chamber angle,” Dr. Nahen said.

Dr. Mardin also commented on the advantages of swept-source OCT for anterior segment imaging in terms of providing higher resolution compared with time-domain technology and greater scan depth than spectral-domain OCT.

“This swept-source OCT platform offers high-resolution images up to a scan depth of 14 mm, and so both the cornea’s and posterior lens surfaces can be imaged with the same high resolution and quality,” he said. “And, the opportunity to assess chamber angle details in relation to the crystalline lens and anterior chamber will be valuable for glaucoma diagnosis. In cases of angle-block, both biometry, i.e., assessment of the anterior segment depth relationship, and OCT gonioscopy can be performed in just a few seconds.”

Swept-source OCT imaging also has benefits compared with Scheimpflug-based systems, Dr. Mardin said. While the latter technology gives accurate measurements of the anterior segment thanks to sophisticated software, it does not provide detailed imaging of the structures being measured, including the cornea, anterior chamber angle, or the crystalline lens interior and surfaces.

“Using an OCT-based system, the examiner learns to understand the measurements by the presentation of high-resolution B-scans of the anterior segment. In the biometry mode an additional detailed view of the posterior outer retinal A-scan signal allows assessment of the quality of the measurements,” he said.

“The ability to directly check the validity of measurements on the images displayed may make surgeons more confident about the measurement results, particularly in patients with complicated pathologies.”

Christian Mardin, MD

E: christian.mardin@uk-erlangen.de

Dr. Mardin has been an investigator in clinical studies and a lecturer for Heidelberg Engineering.

Kester Nahen, PhD

E: Kester.Nahen@HeidelbergEngineering.com