Optical Coherence Tomography Angiography (OCT-A) is a new non-invasive approach to visualizing retinal vasculature and is changing the way physicians see the retinal and choroid (layer below the retina) vasculature. The technology uses light waves to take cross-sectional images of the retina and is similar to ultrasound imaging, except that it uses light instead of sound to provide high resolution images (resolution of 3-5 microns typically).
This technology has dramatically changed retinal care because the images are so high resolution that individual retinal layers can be identified.
OCT-A uses laser light reflectance of the surface of moving red blood cells to accurately depict vessels in different segmented areas of the eye and often minimizes the need for intravascular dye injections. These scans are referred to as A-Scans and when compiled into a B-Scan, can provide cross-sectional information and the ability to analyze differences between scans. This allows detection of zones containing high flow rates (in blood vessels) from zones with minimal flow rates. Computers then help build images of the high and low flow rates, which in turn accurately represent the blood flow (or lack of it).
In addition to OCT-A, we now have AngioAnalytics. This powerful diagnostic tool allows doctors to track early retinal blood vessel changes to determine progression of disease and was recently FDA-approved.
Studies are evidencing that OCT-A can detect retinal microvascular changes in the deep capillary plexus which were previously undetectable. Along with central visual field analyzers, this shows signs of decreased visual acuity and loss of normal blood density in diabetics who show no other signs of diabetic retinopathy. In other words, OCT-A allows doctors to identify diabetic eye disease before it was previously thought to exist and to track that disease for progression. Identifying early diabetic microvascular changes (typically loss of blood vessel density or “drop out”) gives the diabetic managing physician one more tool to intervene in the medical management of diabetes.
This same technology can also be used for other diseases. For example, sub-retinal choroidal vascular membranes (CNVM; think wet versus dry macular degeneration) can be identified by the presence of fluid within or underneath the retina. Another use for OCT-A is in the diagnosis of glaucoma. Studies have shown that OCT-A is just as accurate in identifying early glaucoma as retinal nerve fiber layer measurements (RNFL).
Both RNFL and OCT-A are some of the earliest objective measurements of glaucoma. This allows for early diagnosis of glaucoma and, in cases of ocular hypertension (high eye pressure) without signs of glaucoma, lowering eye pressure to help improve blood perfusion of the optic nerve. This can make the difference between treating and not treating those borderline cases.
Not all doctors have OCT-A as the technology is new, and the cost is moderately high. That said, ten years ago few doctors had OCT technology and now it is readily available. OCT-A is the next step in diagnostics imaging.
Dr. Greg Evans is the founding owner of Evans Eye Care in Rancho Mirage and can be reached at (760) 674.8806.