Optical Coherence Tomographic Angiography in Diabetic Macular Ischemia: A New Step Forward.

Abstract

The fovea is a highly specializedmacular regionwith a unique microanatomythat represents theareaofgreatestvisual acuity. The foveamainlyconsistsofdifferent structures thatarehighly dependent on multilayered capillary plexa for metabolic exchanges. Perifoveal capillary arcade disruption, enlargement of the foveal avascular zone, and reduction of foveal capillary density evaluated with fluorescein angiography (FA) have been negatively correlatedwith visual acuity, suggesting that theymight be useful in evaluating foveal health status.1 Diabetic macular ischemia or infarction is a sightthreatening feature of diabetic retinopathy, characterized by theocclusionof retinal capillaries in themaculaarea,withnarrowing and/or obliteration of precapillary arterioles. The resultinghypoxiacan lead toup-regulationof several growth factors, such as vascular endothelial growth factor, thus contributing to theevolutionofdiabeticmacularedema,which is themost common cause of visual loss in diabetesmellitus. This capillary dropout sometimes can lead to extensive ischemia and subsequent visual loss out of proportion to that expected from any concomitant edema.2 The introduction of optical coherence tomography (OCT) has developed into one of the most important imaging techniques in diabetic maculopathy because of its ability to easily showsignsof intraretinalandsubretinal fluidaccumulation.The OCT examination rapidly became a crucial test to determine whether retreatment in an as-needed regimen is required and provided anatomical confirmation of the visual acuity benefits noted in the treatment of diabeticmacular edema.Nevertheless, retinal vessel changeswere still not directly visualized with OCT examination, and FA remained compulsory. The development of OCT angiography could be a dramatic changebecause it allowsone tovisualize the retinal vessel’s perfusion and distinguish the superficial and deep retinal capillaryplexa.Nevertheless,OCTangiographyhas several limitations:mostof thedevicesarenotyet commercially available, the scanning field is substantially limited, and, sinceOCT angiography only shows blood flowing in the vessels, it is not able to determine pathophysiologic abnormalities (eg, capillary leakage) or differentiate ischemia from infarction. Optical coherence tomographic angiography is a novel imaging technology that enables clear, in vivovisualizationof perfused blood vesselswithout having to use injectable dyes. It provides high-resolution, 3-dimensional images of the retinal and choroidal microvasculature by separating static (tissue) from motion (blood flow) signals.3 The contrast generated between static and nonstatic tissue results in a vascular signal that is analyzedbydifferent typesof algorithms (eg, fullspectrumamplitude decorrelation and split-spectrumamplitudedecorrelation) to calculate thedecorrelationof signal amplitude fromrepeatedconsecutiveBscansat thesamelocation. Optical coherence tomographic angiography has been used3,4 to study different types of choroidal neovascularization inexudative, age-relatedmaculardegeneration.Basedon our experience, OCT angiography is useful for noninvasive monitoringof thestatusofchoroidalneovascularization inagerelatedmacular degenerationbecause functional (blood flow) and morphologic (fluid accumulation) information is simultaneously available from a single OCT angiographic scan. Although some features of active choroidal neovascularization (eg, fluorescein leakageonFA) cannotbe identifiedonOCTangiography, suchmonitoringmayprovide bothqualitative and quantitative data, therefore guiding the decisions for treatment as well as evaluating the response of choroidal neovascularization to its therapy.4 Retinal vein occlusion, macular telangiectasia, and central serous chorioretinopathy have been evaluated usingOCT angiography.More recently, its use has been extended to diabetic retinopathy. Related article page 367 Automated Quantification of Capillary Nonperfusion Original Investigation Research