Microvascular Dropout Within the Lamina Cribrosa in Myopic Eyes With a Parapapillary γ-Zone and Primary Open-Angle Glaucoma

Purpose: The purpose of this study was to elucidate the clinical characteristics and lamina cribrosa (LC) microstructures associated with microvascular dropout (MvD) within the LC (MvD-LC) in myopic primary open-angle glaucoma (POAG) eyes with a parapapillary γ-zone. Methods: POAG eyes with myopia (axial length >24.0 mm) and a parapapillary γ-zone were analyzed. The presence and sizes of parapapillary MvD (MvD-PP) and MvD-LC were evaluated in en face optical coherence tomography angiography (OCTA) images of the deep optic nerve head (ONH) layer. LC microstructures were evaluated using the LC steepness index (LCSI) and LC thickness (LCT) in B-scans. Clinical characteristics and LC microstructures were compared between eyes with and without MvD-LC. Factors associated with the presence and size of MvD-LC were determined. Results: Relative to eyes without MvD-LC, those with MvD-LC had a thinner global retinal nerve fiber layer (RNFL; P = 0.016), worse visual field (VF) mean deviation (MD; P = 0.009), and larger MvD-PP (P < 0.001). The presence of MvD-LC was associated with older age (odds ratio [OR] = 1.082-1.087, P ≤ 0.004) and larger MvD-PP (OR = 1.047-1.048, P ≤ 0.016), but not with LCSI or LCT. The size of MvD-LC was positively correlated with age (P = 0.020) and sectoral LCSI (P = 0.002), and negatively correlated with the global RNFL thickness (P < 0.001), VF MD (P < 0.001), maximum width of parapapillary atrophy (P ≤ 0.010), mean LCT (P = 0.004), and sectoral LCT (P = 0.039). A larger MvD-LC was independently associated with thinner global RNFL (P < 0.001) and worse VF MD (P < 0.001). Conclusions: In myopic POAG eyes with a parapapillary γ-zone, LC microstructures were associated with the size of MvD-LC. Larger MvD-LC was independently associated with more severe glaucomatous damage.