OCT angiography allows early detection and more accurate staging of retinal vascular changes.
Even though the prevalence of diabetic retinopathy (DR), a leading cause of new cases of blindness among adults, is on the rise, new technology can improve the way we manage patients who have diabetes. Optical coherence tomography angiography, or OCT-A, allows for earlier detection and more accurate staging of retinal vascular changes.
NONINVASIVE AND DYELESS
OCT-A is a noninvasive, dyeless system that provides volumetric data about the integrity and blood flow of the retinal and choroidal vasculature. This technology creates 3D maps that show the motion of intravascular red blood cells at one particular point in time. By contrast, fluorescein angiography defines phases based on where dye transverses.
The most common way to view OCT-A information involves pre-set en-face displays from the manufacturer. Each en-face display is generated by compressing a slab consisting of multiple retinal layers into a 2D planar surface.
Two systems with OCT-A capability currently are available: the ZEISS CIRRUS OCT with AngioPlex and the AngioVue Imaging System from Optovue. Others, such as the Nidek RS-3000 Advance with AngioScan, are awaiting FDA approval.
These devices come with advanced eye-tracking technologies that are essential for generating high-resolution OCT-A images.
Benefits of OCT-A include easy and rapid acquisition, short-term repeatability, excellent safety profile and high-resolution microvascular imaging. OCT-A generates volumetric data, allowing you to use depth to localize abnormal vascularization. This is important in differentiating intraretinal microvascular abnormalities (IRMA) from preretinal neovascularization, which is located anterior to the internal limiting membrane. Even normal vasculature can be separated out for viewing and analysis.
OCT-A also lets you correlate vascular and structural abnormalities. OCT-A provides both a conventional 3D macular cube of structural data that allows for visualization of edema and thickening as well as a superimposed 3D map of the retinal vasculature. Microaneurysms and/or IRMA are often adjacent to fluid cysts, and vascular nonperfusion may correspond to areas of retinal cellular disorganization and atrophy.
OCT-A has vast clinical applications when evaluating diabetic eyes. When present, vascular abnormalities are typically in the superficial capillary plexus and the deep capillary plexus en-face displays. The high-resolution microvascular imaging of OCT-A highlights and allows for precise delineation of the foveal avascular zone (FAZ), areas of inner retinal nonperfusion, neovascular complexes and IRMA.
Studies suggest that microvascular abnormalities detected by OCT-A precede the onset of clinically detectable DR. Anomalies found in diabetic eyes without clinical retinopathy include enlargement and an irregular shape of the FAZ, decreased macular vessel density, focal areas of capillary nonperfusion, and microaneurysms.
PROGRESSIVE CAPILLARY CLOSURE
The pathophysiology of DR involves progressive capillary closure with mounting ischemia. Retinal ischemia is typically invisible on funduscopy unless it is acute and accompanied by retinal whitening or is extensive enough to cause large vessel sclerosis. With OCT-A, however, we can easily visualize nnonperfusion. The degree of macular perfusion compromise, particularly of the deep plexus, directly correlates with the severity staging of retinopathy. Extensive retinal nonperfusion in an eye thought to have nonproliferative DR (NPDR) should raise suspicion for budding neovascularization, which typically occurs at the border of perfused and nonperfused zones.
Eyes with extensive nonperfusion and severe NPDR require close monitoring given the risk of progression to proliferative DR. These patients may benefit from early anti-vascular endothelial growth factor (anti-VEGF) treatment even in the absence of diabetic macular edema (DME).
Enlargement of the FAZ and macular ischemia, which may contribute to or be the sole cause of decreased vision in diabetic eyes, are invisible clinically but readily apparent with OCT-A imaging. Studies have shown a correlation between enlargement of the FAZ and worsening visual acuity. Confirmation of macular ischemia is advantageous when the patient experiences decreased vision, even though no macular edema is present.
Also, OCT-A is useful for determining the prognosis in eyes that will undergo anti-VEGF treatment for DME. Poor responders often exhibit significant macular ischemia with large FAZs and numerous microaneurysms within the deep capillary plexus. In these eyes, decreased vision may persist even when the edema resolves.
Perhaps the greatest clinical utility of OCT-A in DR evaluation is the ability to detect early proliferation and differentiate IRMA from true preretinal neovascularization using depth localization. In contrast to IRMAs, which are dilated telangiectasias confined to the retina, preretinal neovascularization is characterized by new blood vessel growth anterior to the internal limiting membrane that often clings to the posterior hyaloid of the vitreous.
The Zeiss Angioplex has a preset en-face display, the vitreoretinal interface (VRI), that corresponds to a segmentation slab of vitreous just anterior to the retina. This was designed to detect and visualize preretinal neovascularization. In diabetic eyes, vascular lesions that are present on the VRI display represent neovascular complexes, not IRMA. The distinction is important, as neovascularization carries a risk for severe vision loss from vitreous hemorrhage and/or tractional retinal detachment.
In my experience, OCT-A has confirmed neovascularization that was questionable or was not apparent via ophthalmoscopy. The high-resolution microvascular detail makes OCT-A an ideal choice for monitoring and ensuring regression of neovascular tissue following treatment.
OCT-A can improve the quality of care you provide individuals with diabetes. As software continues to advance, allowing for automated quantitative analysis of neovascular area, nonperfused zones, FAZ, and macular vessel density, the clinical utility of OCT-A in diabetic evaluation will increase further.
Carolyn Majcher, OD, FAAO, is chief of the Retina Clinic and assistant clinical professor of the Rosenberg School of Optometry University of the Incarnate Word in San Antonio, TX.
WHERE TO FIND IT
Carl Zeiss Meditec, Inc.
800.342.9821 | Meditec.Zeiss.com/USA
800.223.9044 | USA.Nidek.com
866.344.8948 | Optovue.com
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