The advent of the optical coherence tomography angiography (OCTA) enabled in-vivo assessment of deep-layer microvasculature defined as choriocapillaris or vessels within the scleral flange. Moreover, there is accumulating evidence that OCTA-derived parapapillary deep-layer microvasculature dropout (MvD-P) is a characteristic sign suggestive of glaucoma progression.1-3 A recent study by Lee et al. adds to the literature that angular enlargement of the MvD-P is positively associated with the rate of visual field (VF) progression. This highlights the pathogenic role of MvD-P in the progressive change of glaucomatous optic neuropathy.
Interestingly, the extent of the MvD-P angular enlargement was significantly larger in the VF progressor than in the VF non-progressor, while the rate of RNFL thinning did not differ between the two groups. Given that the study population of this study had moderate to advanced disease severity, RNFL may be limited in detecting progression due to the floor effect. MvD-P enlargement can serve as a useful structural parameter indicating disease progression, especially in moderate to advanced glaucoma.
However, the temporal relationship between the MvD-P enlargement and glaucoma progression remains to be elucidated. Decreased metabolic need due to the progressive loss of the retinal ganglion cell (RGC) may lead to reduced ocular perfusion, resulting in the enlargement of the dropout. On the other hand, functional deterioration of the RGC can be derived from the hypo-perfusion of the optic nerve head.4 Future prospective longitudinal studies are needed to clarify the causative role of the parapapillary deep-layer microvasculature dropout in the glaucoma progression.