Using OCTA in optometric practice

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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Evaluating OCTA

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.

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Here are two examples of patients that illustrate the practical use of this technology in an optometry practice.

Case 1

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.

Dilated retinal examination revealed multiple intermediate-sized drusen OD and a grayish-green lesion with associated hemorrhage OS (Figures 1 A, B.) A CNVM OS was suspected, and OCT, OCTA, and traditional FA were performed on the patient.

The widefield OCT of the right eye was essentially normal (Figure 2), displaying drusen with no apparent fluid. The OCT of the left eye revealed a CNVM with associated vitreomacular adhesion with central retinal thickness of 417 µm, evident on both the widefield and raster (Figures 3A and B.)

A 3.0 mm x 3.0 mm OCTA demonstrated the presence of a small CNVM, seen in the outer retina and choroid capillary en face images (Figures 4A, B.)

Traditional FA confirmed the presence of the CNVM (Figures 5A-C.)

The patient was referred to the retina clinic and is currently receiving his second of three scheduled Avastin (bevacizumab, Genentech/Roche) injections OS. The OCTA will be repeated one month after his third injection.

Case 2

A 50-year-old African-American male presented to our clinic for the first time. He had a history of type 2 diabetes for 20 years, and his last A1c was elevated at 8.7 percent. His current medications included insulin and liraglutide for diabetes.

He was treated approximately six months ago by an outside retinal specialist with a series of injections for his right eye and was told he did not need more. However, the patient reported that his vision in the right eye was decreased since the injections, and it was not clear to him why.

Best-corrected vision was 20/50 OD and 20/20 OS. Dilated fundus exam revealed scattered dot/blot hemorrhages and cotton wool spots (CWS) with no obvious edema on clinical exam. The left eye also revealed scattered dot/blot hemes and CWS, fewer that the right eye, with several exudates near the fovea, again with no edema on clinical exam (Figures 6A,B).

OCT confirmed flat maculae OU with no evidence of edema (Figures 7A,B), ruling out diabetic macula edema (DME) as the cause for the vision reduction OD. Therefore, an OCTA and traditional FA were scheduled to evaluate the cause of the reduced acuity OD.

The 3.00 mm x 3.00 mm OCTA revealed an enlarged foveal avascular zone (FAZ) in the right eye, signifying macula ischemia and the cause of the decreased acuity. The FAZ OS was also slightly enlarged, but much smaller when compared to the OD. The traditional FA was deferred because we decided it would not add to the clinical picture or the treatment of the patient.

The patient will be seen again in three months because currently there is no treatment for his macula ischemia.

How OCTA can help

These two cases illustrate how OCTA can be helpful in an optometry practice. The ability to examine the vasculature of the eye without dye is a major breakthrough in retinal care.

By using this technology, we are able to take better care of our patients with retinal disease, make smarter referrals, or be able to hold on to our patients, knowing a referral is not needed.

Reference

1. Pacurariu RI. Low incidence of side effects following intravenous fluorescein angiography. Ann Ophthalmol. 1982 Jan;14(1):32-6.

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