OCTA provides quantitative analysis for diabetic retinopathy, neovascular membrane
Click Here to Manage Email Alerts
OCT angiography is a depth resolved, noninvasive imaging modality that allows for three-dimensional visualization of the retinal and choroidal vasculature.
OCTA uses motion contrast in conjunction with volumetric angiographic data to provide a high-resolution, three-dimensional angiogram.
The OCT angiograms can be segmented anteriorly from the internal limiting membrane and posteriorly to the choroid to precisely identify the location of microvascular abnormality. This data can be cross-referenced with the structural, anatomical data provided with spectral domain OCT (SD-OCT) B-scans. Simultaneous viewing of SD-OCT B-scans and OCT angiograms allows for outstanding visualization of anatomical structure and microvascular perfusion.
OCTA is an excellent imaging platform for common ophthalmic conditions such as age-related macular degeneration, vascular occlusive disease and diabetic retinopathy. Such diseases present with various anomalous findings that are common among a variety of retinal and choroidal vascular diseases.
On OCTA, diseases manifest as the abnormal presence of flow or neovascularization, absence of flow or nonperfusion (capillary dropout) and the appearance of abnormal vessel morphology in the form of aneurysmal dilation or vessel dilation. Due to disparities and subjectivity in OCTA interpretation, quantitative vessel metrics are essential to standardize angiographic analysis. Objective measurement and assessment of these metrics is achieved via quantification software within the OCTA platform.
Measuring, assessing metrics
The OCTA quantification software provides various metrics, including foveal avascular zone (FAZ) measurement, assessment of vessel flow and non-flow areas, and vessel density percentage. The FAZ is defined as the area surrounding the fovea that is devoid of retinal capillaries. The area and shape of the FAZ have been shown to be good indicators of retinal pathologies such as diabetic retinopathy and retinal vascular diseases. These ischemic retinopathies show a statistically significant FAZ enlargement when compared with healthy controls. Quantitative OCTA parameters such as FAZ assessment reveal subclinical macular vasculature change in diabetic eyes that do not manifest clinical retinopathy.
Vessel flow area allows for measurement of anomalous vascular networks, including retinal neovascularization and choroidal neovascular membranes. In some OCTA systems, flow area is measured using a semi-automatic tool where the physician selects the area of interest, and the software identifies the boundaries of the area and provides an area measurement. When applied to numerous areas, the flow area tool provides a summation of all selected regions. Similarly, the non-flow tool can be used to look for small areas of capillary dropout within the superficial capillary network that occur in ischemic retinopathies.
Macular vessel density can also be quantified with this software. Vessel density analytics automatically calculate the percentage of area occupied by OCTA-detected vasculature in an ETDRS grid over the macula and in a color-coded vessel density map with delineated quadrants. This feature is clinically useful, as it provides metrics that are localized over specific areas of interest. There is a direct correlation between disease severity and vessel density; thus as the disease becomes more advanced, vessel density decreases.
Vessel density within an individual may fluctuate, thus quantitative software allows for evaluation of patients over time. The software assesses disease progression with the multi-scan view where the physician follows the patient over time, and the patient acts as his own normative database. Physicians can individualize their measurements in patients with retinal vascular disease by looking at these metrics and seeing how they progress.
Quantitative OCTA reduces the uncertainty of OCTA interpretation by providing objective, reproducible and reliable data that aids in clinical assessment of retinal vascular disease and optic nerve head pathologies.
Diabetic retinopathy
This case highlights the use of OCTA and quantitative software in the diagnosis and management of diabetic patients. The color fundus photograph shows hard exudates inferonasal to the fovea (Figure 1). SD-OCT B-scan shows hyper-reflective spots indicating hard exudates with some structural changes and irregularity in the inner retina (Figure 2). The OCTA segmentation maps of the superficial and deep capillary plexus are shown. Capillary dropout, vascular remodeling around the foveal avascular zone and numerous small microaneurysms are seen in both plexi and appear to be correlated to the areas of hard exudates (Figure 3).
Given the hard exudates and the ischemic changes detected by OCTA, this patient is at increased risk for developing diabetic macular edema and should be monitored closely. Examination and SD-OCT scans should be repeated in 3 to 4 months with a low threshold for referral if the signs worsen.
Figures 4 to 7 illustrate the use and applicability of other quantitative tools in the assessment of diabetic eye disease.
Neovascular membrane
OCT angiography can provide detailed visualization of the anatomy and blood flow of neovascular membranes as well. It has proven to be useful in identifying nonexudative subclinical choroidal neovascularization (CNV) lesions prior to detection with conventional imaging such as OCT and fluorescein angiography. This case highlights the early identification of a nonexudative, occult CNV using OCTA.
The color fundus image shows pigment changes in the macula (Figure 8), and the SD-OCT B-scan reveals a low-lying pigment epithelial detachment without subretinal fluid (Figure 9).
The OCTA segmentation map of most interest in this case is the choriocapillaris slab (Figure 10). The angiogram shows abnormal vasculature/CNV. There is no subretinal fluid on the B-scan, which indicates that the CNV is subclinical in nature. However, it is important to scroll through all of the OCT B-scans to determine whether any fluid is present.
Comanagement with a retina specialist is highly recommended in any case of suspected anomalous choroidal neovascularization. This patient was monitored over the course of 2 years, and sequential images of this lesion were obtained. The multi-scan view shown here highlights the clinical application of this tool and quantitively substantiates the stability of the condition (Figure 11).
OCT angiography is a noninvasive alternative to dye-based angiography that provides highly detailed, three-dimensional, quantitative evaluation of retinal vascular abnormalities. Quantitative analysis of OCTA is essential to standardize objective interpretations of clinical outcome.
References:
- Adhi M, et al. Invest Ophthalmol Vis Sci. 2016;doi;10.1167/iovs.15-18907.
- Al-Sheikh M, et al. Invest Ophthalmol Vis Sci. 2016;doi:10.1167/iovs.16-19570.
- Alibhai A, et al. Ophthalmology. 2017;doi:10.1016/j.oret.2017.09.011.
- Balaratnasingam C, et al. Am J Ophthalmol. 2016;doi:10.1016/j.ophtha.2016.07.008.
- Coscas F, et al. Invest Ophthalmol Vis Sci. 2016;doi:org/10.1167/iovs.15-18793.
- De Carlo TE, et al. Retina. 2015;doi:10.1097/IAE.0000000000000882.
- Di G, et al. Graefes Arch Clin Exp Ophthalmol. 2016;doi:10.1007/s00417-015-3143-7.
- Kashani AH, et al. Retina. 2015;doi:10.1097/IAE.0000000000000811
- Shiihara H, et al. Sci Rep 8. 2018;doi:org/10.1038/s41598-018-28530-7.
- Takase N, et al. Retina. 2015;doi:10.1097/IAE.0000000000000849.
For more information:
Julie Rodman, OD, MS, FAAO, is a professor at Nova Southeastern University in Fort Lauderdale, Fla., and chief of The Eye Care Institute – Broward. She can be reached at: rjulie@nova.edu.
Collapse
Read more about
Click Here to Manage Email Alerts