Optical Coherence Tomography Angiography in Glaucoma

Abstract

Optical coherence tomography angiography (OCTA) is a relatively new, noninvasive, dye-free imaging modality that provides a qualitative and quantitative assessment of the vasculature in the retina and optic nerve head. OCTA also enables visualization of the choriocapillaris, but only in areas of parapapillary atrophy. With OCTA, the movement of red blood cells is used as a contrast to delineate blood vessels from static tissues. The features seen with OCTA in eyes with glaucoma are reduction in the superficial vessel density in the peripapillary and macular areas, and complete loss of choriocapillaris in localized regions of parapapillary atrophy (called deep-layer microvascular dropout). These OCTA changes correlate well topographically with the functional changes seen on visual field examination and structural changes seen on optical coherence tomography (OCT) (ie, parapapillary retinal nerve fiber layer changes and inner retinal layer thickness changes at macula). The OCTA measurements also have acceptable test-retest variability and well differentiate glaucomatous from normal eyes. OCTA measurements can be affected by various subject-related, eye-related, and disease-related factors. Vessel density reduction on OCTA reaches a base level (floor) at a more advanced disease stage than the structural changes on OCT and therefore has the potential to monitor progression in eyes with advanced glaucomatous damage. OCTA also adds information about glaucoma patients at risk of faster progression. OCTA, therefore, complements visual field and OCT examinations to diagnose glaucoma, detect progression, and assess risk of progression.

Figure 1.

Angiography slabs of the optic nerve head scan obtained using spectral domain optical coherence tomography showing the radial peripapillary capillary, RPC (a) and choroid (b) slabs.

Figure 2.

Superficial angiography slabs of the 3×3 (a) and 6×6 (b) mm macular scan obtained using spectral domain optical coherence tomography.

Figure 3.

OCTA features of a glaucomatous eye with mild disease. Optic disc photograph (a) shows inferior neuroretinal rim notch with a correlating superior nasal defect on the visual fields (b) and inferior retinal nerve fiber layer thinning on OCT (c). Composite peripapillary (4.5×4.5 mm scan) and macular (6×6 mm scan) OCTA scan shows reduced vessel density in the inferior region as indicated on the angiography (d) and heat map (e). Vessel density reduction on the macular OCTA scan is less obvious in the inner 3 mm region compared to the outer 3–6 mm region.

Figure 4.

Choroidal OCTA slab of a glaucomatous eye showing the presence of deep-layer microvasculature dropout (MvD) in the inferior region (a). Arrow points to the MvD. Yellow line marks out the boundary of the MvD (b).

Figure 5.

Macular OCTA scan of a left eye showing two types of artifacts on the angiography map; motion artifacts, recognized as vertical bands temporally and duplication of vessels, recognized inferiorly and nasally.

Figure 6.

Vitreous opacity (red arrow on en face map, b) casting a shadow, as seen on the angiography map (a).