Optical coherence tomography angiogram of a 36-year-old woman with a chronic (>1 year) retinal arterial occlusion, inner retinal atrophy involving the superior macula but sparing the fovea, and severe loss of vascular density in most of superior retina. Image shows a depth-encoded pseudo-colored map (red = superficial vasculature, green = middle retinal vasculature, yellow = red/green overlay). (Courtesy of Amir H. Kashani, MD, PhD.)
As a tool for imaging the retinal vasculature, optical coherence tomography angiography (OCTA) may be able to overcome some of the limits of fluorescein angiography (FA), investigators reported at the American Society of Retina Specialist 33rd annual meeting in Vienna.

OCT Gains, FA Fades

Jorge Fortun, MD, reported on a multicenter study that confirmed the use of OCT is increasing while FA is waning.1 While this study did not look at OCTA specifically, it did document, based on an analysis of claims data, the proportion of patients with retinal disease who had OCT increased from 23.2 percent in 2007 to 43.9 percent in 2012 while the rate of FA declined slightly, from 15.7 percent to 14 percent.

Correlation With FA

OCTA results correlate well with FA and even histology, according to investigators at the University of Southern California.2 They recruited 55 subjects—35 with diabetic retinopathy (DR), 10 with retinal vein occlusion (RVO) and 10 with epiretinal membrane (ERM)—and compared OCTA and FA findings.

In DR, lead author Amir H. Kashani, MD, PhD, said, OCTA correlated best with FA when imaging retinal nonperfusion and cotton-wool spots, while microaneurysms yielded the least agreement between the two. The majority of microaneurysms they identified were in the superficial vascular layer with the remainder spanning both vascular layers. But OCTA did not capture the vascular leakage that traditional FA captures so well.  

In RVO, they found that OCTA showed good correlation with nonperfusion on FA, but showed microvascular shunting and pruning more clearly than FA. In both DR and RVO, OCTA showed capillary non-perfusion in superficial and deeper vascular layers. In ERM, OCT angiography showed vessel distortion and noticeable decrease in flow signal in some areas.

“OCTA is likely to be useful for quantitative studies of retinal vascular features as the hardware and software methodologies continue to mature,” Dr. Kashani said.

Macular Perfusion

OCTA can provide quantitative perfusion mapping of retinal blood flow to help detect early pre-edema vascular changes in eyes of diabetes patients, Richard Rosen, MD, and colleagues at New York Eye and Ear Infirmary reported.3 They compared OCTA results in 18 eyes of 10 patients with nonproliferative DR (NPDR), 18 eyes of nine patients with proliferative DR (PDR) and eight eyes of four normal controls. Their goal was to calculate average perfusion density from the superficial, deep and choroidal capillary beds as well as whole volumetric imaging. They used a split-spectrum amplitudinal decorrelational algorithm to generate OCT angiographic images and a customized Matlab skelotinization algorithm to extract perfusion maps.

They found significantly smaller vessel densities in the disease groups vs. the controls. The average vessel density for controls was 0.2477 ±0.0639 (3-mm imaging) and 0.2702 ±0.1006 (6-mm imaging) compared with 0.2012 ±0.0694 (3 mm) and 0.2474 ±0.1048 (6 mm) in the NPDR group and 0.1944 ±0.0692 (3 mm) and 0.2402 ±0.1047 (6 mm) for the PDR group.

“Quantitative perfusion may prove useful in charting diabetic progression prior to onset of edema and anticipating the need for more aggressive interventions,” Dr. Rosen said.  RS

1. Fortun JA, Vaziri K, Moshfeghi AA, Flynn HW. Paper presented at: 33rd Annual Meeting of the American Society of Retina Specialists; July 14, 2015; Vienna, Austria.
2. Kashani AH, Matsunaga BA, Yi J, et al. Optical coherence tomography angiography in retinal disease. Paper presented at: 33rd Annual Meeting of the American Society of Retina Specialists; July 14, 2015; Vienna, Austria.
3. Rosen RB, Muldoon TO, Gentile RC, et al. OCT angiographic perfusion mapping of macular vascularity in diabetic and normal subjects. Paper presented at: 33rd Annual Meeting of the American Society of Retina Specialists; July 14, 2015; Vienna, Austria.