Optical coherence tomography angiography in glaucoma

Abstract

Assessment of the vasculature within the optic nerve, peripapillary superficial retina, macula, and peripapillary choroid can be determined in glaucoma using optical coherence tomography angiography (OCTA). Decreased perfusion within the pre-laminar layer of the optic nerve has been correlated with glaucoma severity. The peripapillary superficial retinal vessel density allows diagnosis and detection of glaucoma progression in a manner similar to the peripapillary retinal nerve fiber layer (RNFL) thickness. Furthermore, decreased peripapillary vessel density of the intact hemiretina or unaffected eye of glaucomatous eyes suggests that vascular changes can occur prior to detectable visual field damage. The accuracy for glaucoma detection of the macular ganglion cell (MGC) thickness compared to macular vessel density has differed among studies. Several studies have reported reduction of macular vessel density as well as its ganglion cell thickness. Results of studies evaluating the parapapillary choroid have shown a greater prevalence of choroidal microvasculature dropout in glaucomatous eyes with a parapapillary gamma zone, which is associated with central visual field defects or glaucoma progression. It remains unclear whether the reduced vessel density in glaucoma is a primary event or secondary to glaucomatous damage. Further studies are warranted to elucidate this question.

Keywords: OCT angiography; choroid; glaucoma; glaucoma progression; macula; microvasculature; optic nerve head (ONH).

Figure 1

Optical coherence tomography angiography (OCTA) depicts vessels inside the optic nerve head (A, arrow), as well as the peripapillary retina (B), peripapillary choroid (C) and the macula with 1 and 3 mm circles around the fovea (D).

Figure 2

Peripapillary vessel density measured in circumpapillary area of elliptical annulus centered on the optic nerve head in healthy normal eyes and primary open angle glaucoma (POAG) eyes. Vessel densities are expressed in numbers, defined as the percentage area occupied by the vessels.

Figure 3

Peripapillary vessel density measurement after excluding large vessels (black vessels, A). Segmentation of large peripapillary vessels (B) also has been shown.

Figure 4

Superficial and deep macular vessels OCTA in healthy and glaucoma eyes. OCTA, optical coherence tomography angiography.

Figure 5

Parapapillary choroidal microvasculature: Left panel shows healthy eye parapapillary choroidal microvasculatures (green arrows). Right panel shows microvasculature dropout in glaucoma (yellow arrows).