Advances in optical coherence tomography (OCT) and OCT angiography (OCTA) may enable more objective and accurate diagnosis of ROP in the future.
By Lynda Charters, Reviewed by J. Peter Campbell, MD, MPH
Optical coherence tomography angiography (OCTA) is a new technology that is gaining importance in ophthalmology clinics as new capabilities are being determined.
Patients with diabetic macular edema and macular degeneration have benefited from its use, and interest is focusing on the use of OCTA in patients with retinopathy of prematurity (ROP).
OCTA has several advantages over fluorescein angiography (FA), in that the former is noninvasive, can resolve the macular plexuses in better resolution than FA, and can provide objective metrics of disease severity, most commonly vessel density or areas of flow void, according to J. Peter Campbell, MD, MPH.
However, no technology is the be all and end all, and OCTA is no exception. Dr. Campbell pointed out that the commercially available OCTA devices provide only a narrow field of view, are limited by artifact, and hand-held OCTA devices are unavailable, which has limited the use of OCTA in children.
Dr. Campbell is assistant professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland.
A few publications have reported on the use of OCTA in young children, he recounted. Vinekar, et al., in 2016 published a report in the Journal of the American Association for Pediatric Ophthalmology and Strabismus that described the use of Optovue’s AngioVue instrument using the “flying-baby technique” in which they demonstrated hyper-reflective material corresponding to recurrent neovascularization seen on FA.
Cross sectional optical coherence tomography angiogram of a patient with retinopathy of prematurity demonstrating choroidal and retinal flow, as well as flow above the internal limiting membrane (blue) representing extra retinal neovascularization (Images courtesy of J. Peter Campbell, MD, MPH)
In 2017, Chen, et al., published case reports in JAMA Ophthalmology in which they used a prototype swept-source (SS-OCT) instrument that was integrated into the operating room microscope to acquire OCTA images intraoperatively for the first time in two young patients.
“Both of these were great advances,” Dr. Campbell said. “However, neither technique is practical for widespread use in ROP screening and diagnosis. Both of these procedures have demonstrated some potential limitations of OCTA in this population.”
The trend for retinal angiography has been toward increasing the field of view over time, Dr. Campbell added. “Many retina specialists have become used to caring for patients by relying on the ultrawide-field FA findings,” Dr. Campbell commented. “OCTA provides higher depth resolution but a more limited field of view.”
Dr. Campbell and colleagues have designed a hand-held SS-OCT/OCTA to facilitate the evaluation of young children with retinal diseases. The investigators hypothesized that OCT/OCTA can provide objective diagnosis of zone, stage, and plus ROP disease.
Here is an example of a physician using the non-contact and contact, hand-held 100-kHz SS OCT device to obtain images in a baby in the neonatal intensive care unit.
The team developed a non-contact and contact, hand-held 100-kHz SS OCT device weighing 381 g with resolutions of 17 µm laterally and 6 µm axially and a 100º field of view. The device was custom designed to obtain OCTA, Doppler OCT, and ultrawide-field (> 100º diameter) OCT images, Dr. Campbell explained.
Dr. Campbell demonstrated noncontact images that were obtained in adult patients in two seconds. Using this device, the field of view and resolution were adjustable and a larger field of view was possible with longer acquisition time and lower resolution.
“By adjusting the scanning pattern and tolerating a bit of motion artifact, we obtained wide-field OCTA images that reliably demonstrated perfusion into zone 2,” Dr. Campbell said. “We also could see the corresponding retinal structure on OCT.”
When obtaining images from babies with ROP, Dr. Campbell explained that clinicians need to determine whether there is added clinical value to this technology, or whether it is just a novel way to look at the developing retinal vasculature.
Optical coherence tomography angiogram of the optic nerve of a patient with retinopathy of prematurity obtained using the handheld device
There are a few reasons why the technology might help in caring for these children.
One is that OCTA can visualize extraretinal neovascularization, which is a critical threshold in disease severity staging, known as stage III. Dr. Campbell offered an example of how OCTA would visualize persistent stage III after treatment that was not observed clinically.
“The cross-sectional OCTA images clearly showed the presence of residual flow above the internal limiting membrane near the border of the perfused and non-perfused retina,” he noted.
A second reason is that quantification of the area of neovascularization might provide an objective biomarker of disease severity that can be tracked over time, he explained.
Third, OCTA can also demonstrate retinal nonperfusion and avascularity with improved contrast over those seen on the corresponding FA images.
“There are several ways this technology might lead to objective diagnosis of plus disease,” Dr. Campbell said. “The Duke group first popularized the idea that there may be structural OCT biomarkers of plus disease, and devised a scale called the VASO score for plus disease evaluation.”
Functional OCT using Doppler OCT may provide another method. “Our hypothesis is that total retinal blood flow, which can be measured using this technology, will correlate with the spectrum of changes seen in pre-plus and plus disease, and may correlate with en face area of stage III disease,” Dr. Campbell said.
Dr. Campbell and colleagues are carrying out a prospective study to evaluate all of these hypotheses in ROP using their hand-held device to obtain wide-field en face OCTA images.
The hope is that as laser speeds increase so will the area covered by OCT. “High-speed OCT can do more than just OCTA, and the ability to obtain wider field structural OCT may have its own added utility in ROP evaluation,” Dr. Campbell said.
Ultrawide-field technology will provide objective diagnosis and quantification of stage, early detection of vitreoretinal traction and retinal detachment, and evaluation of choroidal volume.
“For babies with peripheral disease within the posterior 100º to 110º, we will be able to objectively evaluate the structural and angiographic differences between stages 0, 1, 2, and 3 ROP, and identify the preceding tractional changes leading to the development of retinal detachment,” Dr. Campbell said.
OCT has completely changed the way clinicians care for adults with retinal disease. “In contrast, ROP diagnosis continues to be subjective, based on indirect ophthalmoscopy or fundus photography,” Dr. Campbell said. “No objective methods of diagnosing or monitoring the disease. It is our belief that as OCT systems becomes faster, and more widely available, we will see the same transition in pediatric retina and be able to more objective diagnose and monitor zone, stage, and plus disease in ROP.”
J. Peter Campbell, MD, MPH
This article is adapted from a presentation Dr. Campbell delivered at the 2017 American Society of Retina Specialists. Dr. Campbell has a patent application pending on this technology.