Beta parapapillary atrophy (PPA) is the area adjacent to the clinically delineated optic disc margin where the retinal pigment epithelium (RPE) is absent and hence the underlying sclera and large choroidal vessels are visible. Enhanced-depth OCT imaging allows detailed visualization of the parapapillary region and has shown that the Bruch's membrane (BM) may be present in only part of this region. Therefore, the region of beta-PPA has been divided into gamma-PPA (defined as an area adjacent to the disc border which is devoid of RPE and BM) and beta-PPA+BM (defined as an area with intact BM, but no RPE).1
Complete loss of choriocapillaris in localized regions of PPA, called deep-layer or choroidal microvasculature dropout (CMvD), is a relatively novel finding observed on the choroidal OCTA slabs of glaucoma eyes
The development of OCT angiography (OCTA) has allowed imaging of vasculature in the PPA. Complete loss of choriocapillaris in localized regions of PPA, called deep-layer or choroidal microvasculature dropout (CMvD), is a relatively novel finding observed on the choroidal OCTA slabs of glaucoma eyes.2,3 CMvD has been shown to be a true choroidal perfusion defect using indocyanine green angiography.4 A few recent studies have explored the associations of CMvD in POAG eyes and have reported that CMvD was more frequently seen in glaucoma eyes with greater severity of structural and functional damage,2,5,6 focal lamina cribrosa defects2 and disc hemorrhage (DH).7 The study by Park et al. also reported an association between CMvD and progressive retinal nerve fiber layer thinning in POAG eyes with DH.7 This may mean that CMvD is a marker for glaucoma progression. Suh et al. recently evaluated the association between CMvD and the microstructure of the beta-PPA.8 POAG eyes were divided into two groups based on the microstructure of βPPA; one group with ?PPA and the other with intact BM (βPPA+BM). The groups were matched for glaucoma severity as determined by visual field loss. It was found that CMvD was more frequently (p = 0.004) seen in eyes with ?PPA (75.7%) compared to eyes with βPPA+BM(40.8%). Logistic regression analysis also showed that CMvD was significantly associated with the presence and larger width of ?PPA, but not with βPPA+BM.8
This is an interesting result, but not in complete agreement with the findings of previous studies. An OCT study has shown that ?PPA is associated with older age, high myopia and the absence of glaucoma.1 ?PPA has also been associated with a slower rate of glaucoma progression.9,10 In contrast, previous OCTA studies have shown that CMvD was associated with more advanced glaucoma and glaucoma progression.2,5-7 Therefore, there is need for a better understanding of the complex association between ?PPA and CMvD, and the role of the optic nerve head border tissues in the pathogenesis of glaucoma.
There is need for a better understanding of the complex association between γPPA and CMvD, and the role of the optic nerve head border tissues in the pathogenesis of glaucoma