Beta Zone and Gamma Zone Parapapillary Atrophy in Nonmyopic Eyes

PRCIS: Not only β​​​​-zone but also ɣ-zone atrophy is observed in nonmyopic eyes. The presence of ɣ-zone atrophy reflects optic nerve head canal offset during eyeball expansion, and its directionality is associated with the offset direction. PURPOSE: To evaluate the locations of β-zone and ɣ-zone parapapillary atrophy (PPA) in nonmyopic eyes. METHODS: A total of 151 nonmyopic eyes with an axial length (AXL) of <24.0 mm were included in this cross-sectional study. From the Bruch membrane opening (BMO), the angular locations of the maximal width of β-zone PPA (without retinal pigment epithelium) and ɣ-zone PPA (without Bruch membrane) were compared with that of the central retinal vascular trunk (CRVT)/BMO offset, as a surrogate of lamina cribrosa/BMO offset. Based on the extent and direction of the CRVT/BMO offset, patients were classified into 3 groups: (1) minimal offset (offset index <0.2), (2) temporal offset, and (3) nasal offset. RESULTS: Sixty-four eyes had minimal offset, 53 eyes had a temporal offset, and 34 had a nasal offset. The CRVT/BMO offset showed significant angular correlations with β-zone PPA ( r =-0.209, P =0.026) and ɣ-zone PPA ( r =-0.529, P <0.001). Presence of β-zone PPA was associated with older age [odds ratio (OR)=1.119, P <0.001], longer AXL (OR=2.260, P =0.011), and the presence of ɣ-zone PPA (OR=8.952, P <0.001). Among 56 eyes with ɣ-zone PPA, 26 eyes (46.4%) had their ɣ-zone PPAs on the nasal side, which was associated with the superotemporal direction of the CRVT/BMO offset (OR=1.008, P =0.003). CONCLUSIONS: Both β-zone and ɣ-zone PPAs were found in nonmyopic eyes. Nasally located ɣ-zone PPA was associated with the temporal direction of CRVT/BMO offset, like a mirrored image of myopic PPA. ɣ-zone PPA is not restricted to myopia but represents the offset between the openings of the optic nerve head canal.