Individuals with myopia are at an increased risk of developing primary open-angle glaucoma (POAG). Because of the anatomic traits of myopic eyes, characteristic features of glaucoma seen in these eyes differ from glaucomatous features of non-myopic eyes. Axial elongation of the eye causes a temporal shift of the superior and inferior arcuate RNFL bundles as well as the major retinal vessels.1,2 Therefore, it may be hypothesized that the pattern of retinal vasculature, as assessed by OCT angiography (OCTA), may also be different in glaucoma patients with myopia compared to those without myopia.
In a recent OCTA study, Suwan et al. have examined the peripapillary perfused capillary density (PCD) in 87 myopes with glaucoma (M+G+), 93 non-myopes with glaucoma (M-G+), 17 myopes without glaucoma (M+G-) and 51 non-myopes without glaucoma (M-G-).3 For the purpose of the study, myopes were defined as those with a spherical equivalent of less than -3.0 D. Since most of the participants in the study were over the age of 60 years, their refraction may have been influenced by lenticular changes or pseudophakia, the details of which are not provided by the authors. Hence, definition of myopia based on axial length might have been more appropriate.
The results showed mean global PCD demonstrated a progressive decrease from the M-G- group (41.0%), to the M+G- group (38.4%), to the M-G+ group (31.9%), to the M+G+ group (28.2%; all P < 0.001).3 A similar pattern was seen in the sectoral PCD measurements. The results also showed that the reduction in peripapillary PCD was greater due to glaucoma compared to myopia. The authors concluded that the simultaneous presence of myopia and glaucoma results in a level of microvascular attenuation greater than is observed with either pathology alone.
Multiple factors can influence the PCD measurements of OCTA. A previous study has shown that signal strength index of the OCTA scans can affect PCD measurements.4 In addition, topical anti-glaucoma medications may also affect the OCTA measurements. The results would have been more robust had the authors accounted for all these confounders in their study.