Optical coherence tomography angiography (OCTA) is a new non-invasive imaging technique that allows examination of the retinal vasculature without dye.
It utilizes rapid motion contrast imaging between sequential OCT b-scans in order to look for blood flow through the retinal vessels. By repeating these sequential scans, the retina vasculature can be seen in multiple en face images, representing different levels of the retinal vasculature. These en face images can be seen from the superficial retina to the choroid, allowing a three-dimensional visualization of the retina. As a result, the precise location of the pathology can be visualized by evaluating the appropriate layer. Therefore, the OCTA provides both structural and functional (i.e., blood flow) analysis in a single instrument.
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Unlike traditional fluorescein angiography (FA), which remains the gold standard for the detection of choroidal neovascular membrane (CNVM), as well as neovascularization of the disc or elsewhere, OCTA is non-invasive and easier to obtain. Because FAs are invasive, time consuming, and relatively expensive, they are not always the ideal techniques to use on a daily basis or in a busy clinic.
Further, most optometrists have limited access to traditional FA testing.
Although considered safe, traditional fluorescein dye does have side effects, ranging from nausea and vomiting to anaphylaxis in severe cases.1 In addition, FAs are contraindicated in pregnancy or with concurrent kidney disease.1 Lastly, for patients requiring frequent follow-up exams or those who cannot tolerate the dye, this rapid, non-invasive test is a great alternative.
OCTA has been very useful in age-related macular degeneration (AMD) as well as diabetic retinopathy and related ischemia.
Other advantages are the ability to look for capillary non-perfusion in vein occlusions and optic nerve head perfusion in glaucoma patients.
Its disadvantages include the relatively limited field of view, inability to view leakage, and artifacts that may appear with eye movements.
At this time, Zeiss and Optovue manufacture units approved by the U.S. Food and Drug Administration (FDA) for use in the United States.
Here are two examples of patients that illustrate the practical use of this technology in an optometry practice.
An 81-year-old patient reported to the clinic for his six-month AMD follow-up. He had been diagnosed with dry AMD a few years previously and was taking PreserVision AREDS 2 (Bausch + Lomb) twice a day for the last few years. He reported no change in vision or home Amsler grid (HAG), although he admitted that he rarely performs HAG.
Entering acuities were 20/30 OD and 20/70 OS, demonstrating reduced vision OS from 20/30 six months prior.