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OCT angiography has potential to improve diagnosis and monitoring of corneal vascularization
Three published papers show that the technology may be used for imaging and delineating abnormal corneal vasculature.
OCT angiography is designed and optimized for the retina, but it offers potential for the diagnosis and monitoring of several conditions that affect the cornea, according to one specialist.
“With a modified focus and algorithm, OCTA can be used for imaging and delineating corneal vascularization, which is seen in any insult to the cornea, including patients with ocular surface disease and limbal stem cell deficiency,” Marcus Ang, FRCS, said in an interview with Ocular Surgery News.
From diagnosis of a condition to monitoring of treatment, this new imaging modality can also be applied to infections, lipid keratopathy or even damage following chemical injury. Another indication might be the postoperative monitoring of rejection after corneal transplantation.
“Vascularization is a key risk factor of graft rejection. OCTA allow us to detect and quantify new vessel growth in patients before and after corneal grafts,” Ang said.
Studies
Ang and colleagues have published three studies that look at various applications of OCT angiography in the cornea. The first, published in Ophthalmology, described the OCTA technique adapted for the cornea and showed OCTA images of normal limbal architecture to demonstrate that the technique was repeatable. In the second paper, published in the British Journal of Ophthalmology, OCTA was used in 20 eyes with very extensive areas of corneal vascularization.
“We showed that we can use OCT angiography to monitor and also diagnose the abnormal vessels, and this might have huge implications for future studies. Current clinical trials evaluating anti-VEGF injections for the cornea often use photographs or ICG angiography, which suggests a potential role of OCTA in the future,” Ang said.
More recently, Ang and colleagues looked at patients who had indocyanine green (ICG) angiography and OCTA performed and found that the two modalities were comparable in the ability to successfully delineate the vessels.
“These results are quite promising and show that there are many potential clinical applications of OCT angiography, for diagnosis, presurgical assessment and post-treatment monitoring,” Ang said.
A noninvasive technique
In the past, there was no alternative for the evaluation of corneal vascularization other than photographs or ICG angiography. However, ICG angiography is invasive and time consuming, and exposes the patient to the potential risk of an adverse reaction.
“ICG angiography is hardly performed in these patients with corneal vascularization due to the risk-benefit ratio. Now with OCTA within 3 to 5 seconds we can image corneal vascularization using a non-contact technique. The technique has a real potential to add further information to our imaging modalities in terms of evaluating the cornea and vessels. As we were already using the OCT to image the cornea, the angiography function adds another dimension simultaneously,” Ang said.
Ang uses OCTA for the anterior segment and cornea in his daily practice and also collaborates with glaucoma specialists to look at drainage, flow, blood vascularization after trabeculectomy and potential drainage patterns. In his studies, he used the commercially available AngioVue (Optovue) system, adapting the focus and algorithm for the cornea and anterior segment, although other commercially available systems are currently being developed for the cornea.
Current limitations
Ang said there are limitations that need to be overcome.
“The limitations we have in imaging the retina are similar to that in the anterior segment. Motion correction is a big issue, which is compounded by various forms of image artifacts, a need to improve the speed of acquisition, as well as field of view. The size of the area that can be scanned is currently quite limited. Specifically for the anterior part of the eye, segmentation is a big limitation because the current software recognizes transverse scans of retinal tissue layers but it doesn’t automatically detect the layers of the cornea,” he said.
However, he is confident that the technology will quickly improve because companies are aware that there is a wide scope for anterior segment upgrades of OCTA machines.
“OCT angiography for the anterior segment is still in its early days. There are plenty of limitations users have to be aware of, but certainly it is very exciting because current alternatives are invasive, time consuming and nobody uses them anyway,” Ang said. “We need to improve and wait for an official anterior segment algorithm, which I am sure will be released soon.” – by Michela Cimberle
- References:
- Ang M, et al. Br J Ophthalmol. 2015;doi:10.1136/bjophthalmol-2015-307338.
- Ang M, et al. Br J Ophthalmol. 2016;doi:10.1136/bjophthalmol-2015-307706.
- Ang M, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2015.05.017.
- For more information:
- Marcus Ang, FRCS, can be reached at Singapore National Eye Centre, Singapore Eye Research Institute, 11 Third Hospital Avenue, Singapore 168751, Singapore; email: marcus.ang@snec.com.sg.
Disclosure: Ang reports no relevant financial disclosures.