OCT Angiographic Study of Optic Disc Perfusion in Glaucoma

Abstract

 

Purpose

 

To measure optic disc circulation in glaucoma patients using optical coherence tomography (OCT) angiography.

 

Methods

 

One eye of each subject was scanned by a high-speed (100K A-scan/sec) 1050 nm wavelength swept-source OCT. The optic disc angiography scan spans 3x3 mm and comprises 200x200x8 A-scans acquired in 3.4 sec. Flow was detected using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Motion artifacts were removed by scanning 4 orthogonal raster scans, using an algorithm to estimate and correct motion, then merging the 4 motion corrected volumes to improve signal. In the merged scan volume, en face maximum projection was used to obtain 2D disc angiograms, from which average decorrelation values (flow index) were computed from the disc. Visual field (VF), disc photography, and confocal scanning laser ophthalmoscopy (cSLO, HRT II) were used to provide standard glaucoma diagnostic evaluation. Comparisons between glaucoma and normal groups were analyzed by Wilcoxon rank sum test. Correlations between SSADA flow index and other measures of function and structure were assessed by linear regression.

 

Results

 

Ten glaucoma subjects (6 perimetric, 3 preperimetric, and 1 ocular hypertensive) and twenty normal human subjects were compared. In normal discs, a dense microvascular network was visible on OCT angiography (Fig. 1B). This network was visibly attenuated in all glaucoma subjects (Fig. 1E). The intra-visit repeatability, inter-visit reproducibility, and normal population variability of SSADA-based optic disc flow index were 1.1%, 6.6%, and 4.8% CV respectively. In the glaucoma group, the disc flow index was reduced by 19%. These reductions were significant even after accounting for age, cup/disc ratio (photograph), and rim area (cSLO). The disc flow index was significantly (P<0.01) and highly correlated (R = -0.80) with VF pattern standard deviation.

 

Conclusions

 

OCT angiography, generated by the new SSADA algorithm, is a highly reproducible method for the measurement of optic disc perfusion. It could be useful in the evaluation of glaucoma and glaucoma progression.

 

 

Disc photographs (A, D) and OCT angiograms (B, E, en face maximum projection) and cross-sectional angiograms (C, F, overlaying on OCT reflectance in grey scale) in representative normal (A-C) and preperimetric glaucoma subjects (D-F). In (B) and (E) the solid circles indicate the discs.

 

Keywords: 627 optic disc • 436 blood supply