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Editors Selection IGR 24-3

Clinical Forms of Glaucoma: OCT-A in POAG and NTG

Comment by Linda Zangwill on:

74388 Optical coherence tomography angiography of the peripapillary capillaries in primary open-angle and normal-tension glaucoma, Igarashi R; Ochiai S; Sakaue Y et al., PLoS ONE, 2017; 12: e0184301

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Optical coherence tomography angiography (OCTA) has facilitated the visualization of retinal vascular architecture of the optic nerve head and macula. The ability to visualize the vascular system at different layers of the retina has immediate benefit for characterizing and monitoring various retinal diseases including diabetic retinopathy, age-related macular degeneration, and retinal vascular occlusions. The advantages of utilizing OCTA for detecting and monitoring glaucoma compared to standard measures such as retinal nerve fiber layer thickness (RNFLT) is less clear and is the topic of numerous investigations. Igarashi and colleagues¹ assessed the relationship between the vascular architecture of the radial peripapillary capillaries (RPC) and severity of visual field damage in a relatively small study of 20 open angle glaucoma and 32 normal tension glaucoma with moderate to advanced disease. The investigators evaluated RNFL thickness and flow density (more commonly known as vessel density) along with 2 new metrics: the disappearance angle of the RPCs, and the angle of the retinal nerve fiber layer (RNFL) defect. They found that flow density and the disappearance angle of the RPC was independently associated with visual field mean deviation. Igarashi's results confirm numerous other reports that vascular dropout of the RPCs measured by vessel density is positively associated with severity of glaucomatous visual field damage.^2-4

Although not highlighted in the discussion, the investigators also found that both RNFL defect angle and RNFL thickness are more strongly associated with visual field MD and PSD than the OCTA metrics, particularly in the normal tension group. In addition, the authors conclude that flow density and the disappearance angle of the RPCS were significantly and independently correlated with glaucoma functional and structural damage; however no multivariable analysis was completed to determine whether these parameters were independently associated with severity of glaucoma when other measures, such as RNFL thickness were included in the model. The authors also suggest that "progression of glaucoma may be predicted by the disappearance angle of the RPC"; such statements should be reserved for inference from longitudinal studies as cross-sectional studies cannot directly inform on prediction or progression of disease.

The question remains whether the visualization and quantitation of retinal vasculature will provide additional information that will change glaucoma clinical decision making when RNFL thickness and ganglion cell layer measurements are already available to the clinician

The high-resolution visualization of perfused retinal vasculature provided by OCTA has already begun to improve our understanding the role of the retinal vascular system in the pathophysiology of glaucoma. The question remains whether the visualization and quantitation of retinal vasculature will provide additional information that will change glaucoma clinical decision making when RNFL thickness and ganglion cell layer measurements are already available to the clinician. Longitudinal studies are needed to answer this important question.

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