Automated Quantification of Macular Ischemia Using Optical Coherence Tomography Angiography in Diabetic Retinopathy

Abstract

 

Purpose

 

To quantify macular ischemia in diabetic retinopathy (DR) using optical coherence tomography (OCT) angiography.

 

Methods

 

The macula of 7 eyes of healthy control subjects and 7 eyes with various levels of DR were imaged with a commercially available 70 kHz OCT (RTVue XR, Optovue, Inc). Three dimensional (3D) OCT angiography scans were acquired over 3×3 and 6×6 mm regions by using 5 repeated B-scans at 216 raster positions, each B-scan consisting of 216 A-scans. Flow was detected with the split-spectrum amplitude decorrelation angiography (SSADA) algorithm and motion artifact was removed by 3D orthogonal registration and merging of 2 scans. Retinal angiogram was created by projecting the flow signal internal to the retinal pigment epithelium in en face orientation. Parafoveal and perifoveal vessel density were defined as the percentage of pixels with detectable flow in the respective regions (Fig. 1B1). The threshold for detecting flow was set at 2.33 standard deviations above the mean signal within the foveal avascular zone (FAZ) (0.6 mm circle) of the control eyes. An automated algorithm detected the area of macular low-perfusion, defined as the area with flow signal below threshold within 5.5 mm from the foveal center including the FAZ. (Fig. 1C).

 

Results

 

In 2 cases of DR, 6×6 mm scans were excluded due to failed registration. 3×3 mm scans of these two cases were used for the calculation of parafoveal vessel density. Compared to normal controls, the parafoveal and perifoveal vessel density were significantly reduced, low-perfusion area was significantly greater in eyes with DR. Areas of low perfusion in OCT angiogram corresponded to ischemic areas in fluorescein angiography.

 

Conclusions

 

OCT angiography can quantify retinal ischemia and offers an objective and rigorous method of grading macular ischemia in diabetic retinopathy.  

 

Automated detection of nonperfusion in normal control (upper panels) and diabetic retinopathy (lower panels). White dashed circle: normal foveal avascular zone (0.6 mm diameter). Area between white and blue dashed circles: parafoveal zone. Area between blue and green dashed circles: perifoveal zone. Low-perfused areas (blue in C) are detected by identifying flow signals lower than a set cutoff point.

 

 

Comparison of macular perfusion between normal controls and diabetic retinopathy