OCTA Helping to Confront the Complexities of Uveitis Care
By Dilraj S. Grewal, MD
Ongoing research into OCT angiography (OCTA) supports its usefulness in the diagnosis and management of many ocular diseases that affect the retinal vasculature, including uveitis. Based on the knowledge that has emerged, I routinely include OCTA as I evaluate uveitis patients beginning with baseline imaging. When findings involve macular pathology, where OCTA’s chief capabilities currently lie, I often rely on it for follow-up rather than fluorescein angiography (FA) or indocyanine green angiography (ICGA) because it is noninvasive, no-risk, and quicker to acquire. This, however, comes with two caveats. The ocular media must be clear enough to enable good scan quality, and the macular anatomy must not be distorted to the extent that the software is unable to accurately segment the retinal layers. Uveitis patients often may not meet these criteria due to inflammation impacting media clarity, common comorbidities such as cataract or posterior synechiae, or severe macular edema.
With those caveats in mind, when a good quality scan can be obtained in a uveitis patient, OCTA provides very valuable information.
Capillary Plexus Vessel Density Quantification
One parameter I evaluate with OCTA in uveitis patients is the severity of ischemia in the superficial and deep capillary plexuses. OCTA software provides automated quantitative metrics for vessel density in these retinal layers as well as the size of the foveal avascular zone. It also offers the ability to construct montage scans that show ischemia (and retinal neovascularization) in a larger area of the retina extending beyond the arcades (Figure 1). Eyes with active uveitis, even in the absence of macular edema, may have reduced vessel density and this can be an additional metric for monitoring response to treatment.1 In addition, the severity of retinal ischemia is an important prognostic indicator. Ischemia in the foveal and parafoveal region indicates a relatively poor visual prognosis.
Figure 1. Wide-field montaged OCTA imaging shows ischemia and neovascularization beyond the retinal arcades.
It’s also being recognized that OCTA can be informative in cases of retinal vasculitis because it identifies small areas of ischemia in the capillary plexus surrounding the larger retinal vessels (Figure 2). To monitor the severity and progression of retinal vasculitis affecting the posterior pole, OCTA may be used as an adjunct or even a non-invasive alternative to FA.
Figure 2. In addition to identifying ischemia in the capillary plexuses, OCTA can detect ischemia in the capillary plexus surrounding larger retinal vessels, making it useful in cases of retinal vasculitis.
Changes in the Choriocapillaris and Superficial Choroid
Another strength of OCTA in uveitis is its ability to detect changes in the choriocapillaris, as well as the superficial and deeper layers of choroid that appear in many uveitic entities. For example, flow voids, which appear in OCTA images as dark spaces, correlate to areas with absence of blood flow on structural OCT. The significance of these flow voids was initially unknown, but data based on correlation with ICGA shows that they represent areas of choroidal or choriocapillaris ischemia. With detection of flow voids, more aggressive anti-inflammatory treatment can be administered because some restoration of blood flow with corresponding improvement in vision is possible (Figure 3). On the other hand, if left untreated, choroidal or choriocapillaris ischemia can lead to permanent loss of the choriocapillaris and irreversible loss of blood flow that causes loss of the overlying outer retinal layers. Interestingly, flow voids may appear larger on OCTA than on ICGA. It’s unclear at this time how much of the difference is due to artifact versus a true pathological difference. Flow voids can be seen in both infectious and noninfectious uveitis.2-5
Figure 3. OCTA detects flow voids that represent areas of choroidal or choriocapillaris ischemia (dark areas, upper left) and corresponding areas of lack of blood flow on OCT B-scan (white arrow, lower left). With more aggressive treatment, some restoration of blood flow (upper and lower right) and improvement in vision are possible.
CNVMs vs. Inflammatory Lesions
OCTA excels in its ability to detect choroidal neovascular membranes, including small choroidal neovascular nets that may not be seen on OCT and may be missed on FA. It’s important in uveitis patients to recognize these nets because they often indicate that underlying inflammation is inadequately controlled. As such, this finding should prompt adjustment of anti-inflammatory therapy in addition to anti-VEGF therapy, which may also be needed.
Improvements Continue to Materialize
A steady stream of improvements has been made to OCTA technology. Improvements include improved depth of penetration, better scan quality and speed, and the previously mentioned quantitative metrics and wider field of view with montaged scans that help to improve disease monitoring. Ongoing improvements will further enhance OCTA’s ability to uncover previously unrecognized pathologic changes that may help foster earlier diagnosis and more individually targeted treatment.
1. Wintergerst MWM, Pfau M, Müller PL, et al. Optical coherence tomography angiography in intermediate uveitis. Am J Ophthalmol. 2018;194:35-45.
2. Mandadi SKR, Agarwal A, Aggarwal K, et al., for OCTA Study Group. Novel findings on optical coherence tomography angiography in patients with tubercular serpiginous-like choroiditis. Retina. 2017;37(9):1647-1659.
3. Borrelli E, Sarraf D, Freund KB, Sadda SR. OCT angiography and evaluation of the choroid and choroidal vascular disorders. Prog Retin Eye Res. E-pub ahead of print: July 27, 2018.
4. Heiferman MJ, Rahmani S, Jampol LM, et al. Acute posterior multifocal placoid pigment epitheliopathy on optical coherence tomography angiography. Retina. 2017;37(11):2084-2094.
5. Vu DM, Thomas AS, Finn AP, Grewal DS. Choriocapillaris flow voids in cryptococcal choroiditis using optical coherence tomography angiography. Retin Cases Brief Rep. E-pub ahead of print: Jan. 25, 2018.
Dr. Grewal is a vitreoretinal surgeon and uveitis specialist at the Duke Eye Center in Durham, N.C. His work includes involvement in clinical trials evaluating new treatments and imaging modalities.