OCT + OCTA capable of imaging both structure and function

Take-home message: A new dual-modality imaging system adds optical coherence tomography angiography to conventional OCT to rapidly visualize blood flow in the retina and layers of choroidal neovascularization.

Reviewed by Richard Rosen, MD

New York-As drugs have been developed to treat choroidal neovascularization (CNV) by manipulating retinal thickness, it is increasingly important to monitor changes in the blood vessels at the microvascular level.

A dual-modality optical coherence tomography (OCT) and OCT angiography (OCTA) system (AngioVue Imaging System, Optovue), which received FDA clearance in February, gives clinicians a three-dimensional picture of all the capillary beds of the retina that they can use to guide treatment decisions and personalize patient care.

“This three-dimensional access to these different capillary beds empowers the clinician in ways that we couldn’t even imagine a few years ago,” said Richard Rosen, MD, professor and vice chairman, surgeon director, retina service chief, director of research, ophthalmology department, New York Eye and Ear Infirmary of Mount Sinai. Dr. Rosen has studied the technologies involved in OCTA in his lab and in collaboration with others and had access to the system as an investigational device through the infirmary’s institutional review board.

“OCTA is like the ‘Swiss Army knife’ of vascular monitoring,” Dr. Rosen said. ”We really couldn’t look at the radial peripapillary capillary with fluorescein.

“The only way we could visualize them prior to this technology was in the laboratory in histology slides or with adaptive optics imaging, but that’s not a practical clinical tool yet,” he said. “We couldn’t see the choriocapillaris very well, and that’s another vascular bed that we now have access to. And we really couldn’t differentiate the superficial deep or intermediate vascular beds.”

With OCT angiography, surgeons have a more complete appreciation of these capillary beds. Physicians can see extraordinary details of different types of choroidal neovascularization, Dr. Rosen noted.

“Retinal physicians are now trying to figure out how to better classify choroidal neovascularization using this technology, in order to predict which patients require treatment, how to judge response to treatment, and how to determine membrane stability, which may not require re-treatment,” he said.

More about OCTA

OCTA is a noninvasive, dyeless technique that uses light rays to form detailed three-dimensional images of the retina and visualize the presence or absence of flow in the blood vessels.

“OCTA adds a functional layer of information on top of the anatomic information from the regular OCT,” said Tony Ko, PhD, vice president of research and development at Optovue. “There are things you can see with this technology that you can’t with previous techniques. Looking directly at the vessels with OCTA rather than using standard OCT to view a marker or sign of neovascularization could change the way patients with diabetic retinopathy or choroidal neovascularization are treated.”

The system can produce an image of a small segment-3 by 3 mm or 6 by 6mm-of the central macula or optic nerve or piece together multiple small segments to create a larger montage.

Researchers have been exploring various approaches to OCTA for more than a decade. Originally it was a research tool and was not ready for commercialization until obstacles to clinical use such as long visualization times were overcome, Dr. Ko said.

Many companies have developed or are working on OCTA systems, but Optovue was the first to have a commercially available product, released internationally in late 2014.

The system relies on two main technology advances from the past few years: motion correction technology, which can remove or reduce many motion artifacts, and split-spectrum amplitude-decorrelation angiography (SSADA). SSADA is an algorithm that improves the signal to noise ratio of flow detection, producing high quality vascular images with lower acquisition times, according to Dr. Ko.

Quantitative analysis software for the AngioVue gives clinicians the ability to measure very small changes in the perfusion of the retina. Dr. Rosen’s adaptive optics lab worked on this software in conjunction with Optovue.

Using this software, researchers have also devised a linear-numerical scale for use in patients with diabetic retinopathy, correlating perfusion density with the disease stage.

“With this technique we can look much earlier and see areas where the capillaries close off, so we think we could detect diabetic retinopathy at a much earlier stage,” Dr. Rosen said.

“The perfusion density mapping and the quantitation will turn out to be game changers as a way of early monitoring for a lot of diseases. These measures will help foster adoption of this  (OCTA) technology,” Dr. Rosen said.

These applications are available on systems sold in markets outside of the United States and will soon be available in the United States under investigational labeling requiring IRB approval until they receive clearance from the FDA.

“There’s a huge interest in OCTA, and I think it will expand out into the greater ophthalmic community in a very short time,” Dr. Rosen said. He has been collaborating with glaucoma specialists and neuro-ophthalmologists at the New York Eye and Ear Institute on additional clinical applications for the new technology.

“Eventually all of the companies will have different versions of this technology, and it will become a standard of care in terms of evaluating the retina clinically,” Dr. Rosen said. “It’s very, very quick; painless; it can be done on a regular basis, and it gives the clinician a much broader idea of what’s happening in the retina besides just thickness or structural change. It’s really revolutionary, and we’re just at the beginning of this.”

Richard Rosen, MD

E: rrosen@nyee.edu

Dr. Rosen is an investigator with a consultant agreement with Optovue. Work done in his Adaptive Optics Laboratory at the New York Eye and Ear Infirmary of Mount Sinai served as the basis and stimulus for the perfusion density software component of the AngioAnalytics, for which he shares some intellectual property.