This article is more than 5 years old. Information may no longer be current.
OCT angiography a promising imaging modality for evaluation of microvasculopathy
Click Here to Manage Email Alerts
OCT angiography, or OCT-A, was recently developed to provide three-dimensional noninvasive viewing of the retinal and choroidal vasculature and blood flow estimation at the microcirculation level. OCT-A is based on mapping erythrocyte movement over time by comparing sequential OCT B-scans at a given cross-section. OCT-A has now been explored to study different eye diseases including choroidal neovascularization, polypoidal choroidal vasculopathy, diabetic retinopathy, macular telangiectasia, glaucoma and retinal venous occlusion. This is an exciting era in evaluation of microvasculopathy.
Fluorescein angiography (FA) and indocyanine green angiography (ICGA) are considered the gold standard for imaging the retinal and choroidal vasculature. However, they are invasive and time-consuming and provide only two-dimensional image analysis without quantifiable parameters. Furthermore, they cannot separately visualize the intraretinal structures of the major capillary networks. The ability to detect microvasculature alterations has also been limited by the superposition of the capillary networks and leakage in FA. OCT-A can be obtained with both spectral-domain OCT and swept-source OCT technologies. There are several key advantages of OCT-A over traditional FA and ICGA.
OCT-A is able to separately detect the superficial vascular network in the ganglion cell layer, the deep vascular network in the outer plexiform layer and choriocapillaris below the retinal pigment epithelium without intravenous dye injection, providing depth-resolved visualization of the retinal and choroid vasculature and blood flow. Furthermore, OCT angiograms are co-registered with OCT B-scans from the same area, allowing for simultaneous visualization of structure and blood flow for clinical interpretation. Importantly, the retinal and choroidal vasculature can be quantified by advanced image processing methods (eg, foveal avascular zone area and vessel density), which provide objective and quantitative assessment of the vasculature. Moreover, OCT-A can generate data on vascular flow to quantify retinal or optic disc perfusion and choroidal blood vessel flow, independent of time and dye injection. For example, it has been reported that glaucomatous optic discs have significantly diminished flow indices in the radial peripapillary capillaries compared with normal discs. In addition, OCT-A can detect features (eg, capillary dropout) that could be obscured by leakage in FA.
Studies have come up with advantages of OCT-A in distinguishing different types of choroidal neovascular membranes, their exact morphology, and precise qualitative and quantitative assessment to aid in the diagnosis and monitoring after therapy. It has also showed good evidence to be better than FA in documenting and monitoring macular telangiectasia type 2 lesions. OCT-A technology is a potential clinical tool for branch retinal venous occlusion diagnosis and follow-up, providing stratigraphic vascular details that have not been previously observed by standard FA. The normal retinal vascular nets and areas of nonperfusion and congestion can be identified at various retinal levels by OCT-A. Taken together, this information can assist clinicians in the diagnosis and guide decision for treatment as well as evaluate the response of therapy.
However, challenges remain to translate OCT-A into routine clinical practice. First, current OCT-A only has a small field of view (largest view is currently 6 mm × 6 mm), which is limited by scanning speed. Larger fields of view will be critical to evaluate vascular abnormalities at more peripheral regions in a variety of disease states. Second, OCT-A is unable to detect dynamic patterns of dye transit and leakage, which is important for assessment of vascular permeability. Furthermore, the ability of OCT-A to detect microaneurysms is lower than that of FA, as some microaneurysms are nonperfused.
Third, there are no standardized grading procedures or protocols for assessment of OCT angiograms. Validation data for OCT-A (eg, reproducibility, agreement with current gold standard and correlation with clinical outcomes) are still very limited. Fourth, automated and robust methods for identifying specific retinal vascular layers (particular in diseased eyes) and quantitative assessment of retinal capillary network are lacking. Such development will enhance the clinical usefulness in the diagnosis, staging and monitoring of eye diseases. Fifth, image artifacts are very common in OCT-A because it is extremely sensitive to motion. More advanced software to neutralize artifact while maintaining adequate intensity and visibility of pathologic vascular complexes is required. Also, other factors such as media opacity and segmentation errors should be taken into account when OCT angiograms are interpreted.
In summary, detailed retinal and choroidal vascular layers can now be imaged easily using the new OCT-A technology without intravenous dye injection. OCT-A is a promising and useful imaging modality for evaluation of microvasculopathy although there are significant challenges in the interpretation. It is believed that OCT-A will be increasingly incorporated into clinical practice.
References:
Coscas GJ, et al. Retina. 2015;doi:10.1097/IAE.0000000000000766.
Couturier A, et al. Retina. 2015;doi:10.1097/IAE.0000000000000859.
Hwang TS, et al. JAMA Ophthalmol. 2016;doi:10.1001/jamaophthalmol.2015.5658.
Hwang TS, et al. Retina. 2015;doi:10.1097/IAE.0000000000000716.
Jia Y, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2014.01.034.
Jia Y, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2014.01.021.
Jia Y, et al. Proc Natl Acad Sci USA. 2015;doi:10.1073/pnas.1500185112.
Kashani AH, et al. Retina. 2015;doi:10.1097/IAE.0000000000000811.
Liu L, et al. JAMA Ophthalmol. 2015;doi:10.1001/jamaophthalmol.2015.2225.
Spaide RF, et al. JAMA Ophthalmol. 2015;doi:10.1001/jamaophthalmol.2014.3616.
Spaide RF, et al. Retina. 2015;doi:10.1097/IAE.0000000000000765.
Thorell MR, et al. Ophthalmic Surg Lasers Imaging Retina. 2014;doi:10.3928/23258160-20140909-06.
Wang X, et al. Graefes Arch Clin Exp Ophthalmol. 2015;doi:10.1007/s00417-015-3095-y.
For more information:
Dennis S.C. Lam, MD, FRCOphth, can be reached at State Key Laboratory in Ophthalmology, Sun Yat-Yen University, 54 South Xianlie Road, Guangzhou 510060, People’s Republic of China; email: dennislam.gm@gmail.com.
Disclosure: The authors report no relevant financial disclosures.