Optical Coherence Tomography Angiography of Optic Disc Perfusion in Primary Open Angle Glaucoma

Abstract
Background: Glaucoma is a major disease that potentially results in irreversible blindness. Optical coherence tomography angiography (OCTA) is a novel technique for evaluation of retinal vascular changes. Using OCTA have provided useful information about the papillary and peripapillary microvas-culature. Optic nerve head perfusion measurements.
Aim of Study: To investigate optic disc perfusion differ-ences between normal and primary open angle glaucoma eyes using optical coherence tomography angiography (OCTA).
Methods: This prospective comparative cross-sectional selective pilot study was performed on 15 eyes of 15 primary open angle glaucoma (POAG) patients and 20 eyes of 20 healthy age-matched controls. OCT and OCTA were performed using swept source TOPCON 3D OPTICAL COHERENCE TOMOGRAPHY DRI OCT Triton. The optic nerve head (ONH) was imaged with a 4.5x4.5mm scan and assessed in 4 different levels of segmentation; the superficial Papillary, deep papillary, outer retina level and choroidal level. Density map images gave qualitative data and quantitative assessment, these images were processed using Image J program (IJ 1.46 r edition) for determining vascular density index (VDI). The Central corneal thickness, retinal nerve fiber layer thickness (RNFLT), ganglion cell layer thickness (GCLT), stereometric parameters cup/disc area, rim area, cup volume and visual field parameters [mean deviation (MD), pattern standard deviation (PSD) were tested for correlation with vascular density.
Results: The vascular density index in the OCT angi-ograms, as a quantitative assessment, of the optic nerve head (ONH) perfusion was significantly lower in the glaucoma group when compared with the normal age matched control groups. This reduction was significant in POAG with average VDI was reduced by 6.29%. However, in qualitative assessment the dense microvascular network that was visible on OCTA in normal discs, was visibly attenuated with marked capillary drop out in subjects with glaucoma. This reduction in vascular density i.e. ischemia may have a primary element as detected by decreased VDI at choroidal level POAG that reduced by 17.37%. In addition, it may be secondary to elevated IOP that has direct impact with decrease VDI at superficial papillary level that is marked in cases with high IOP. The vascular density index was correlated significantly with all functional and structural parameters and the rate of disease progression and severity.
Conclusions: OCTA may offer insights into the patho-physiology of glaucomatous damage and understanding the role of vascular factors in the pathogenesis of the disease. Hence, it may be a promising technology in glaucoma man-agement.