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(A) Tortuosity measurement steps of a sample vessel segment. (B) Different zones of retina: zone A (region from 0 to 0.5 ONH diameters away from the ONH margin), zone B (region from 0.5 to 1 ONH diameters away from the ONH margin), and zone C (region from 0.5 to 2 ONH diameters away from the ONH margin).
