Fig. 1

The optic disc has changed from the initial (a) to the final (b) visit. The distance from the fovea to the temporal margin of parapapillary atrophy was unchanged (white double arrows of same length), while the γ-zone was elongated. The horizontal diameter of this optic disc had been reduced to 0.772 of its original size. To account for the optic disc change of this patient, 39.5° of tilt by arccosine (0.772) was required. The curvatures along the Bruch’s membrane (linear lines) and anterior sclera (dotted lines) are drawn at both the initial (red lines) and final (blue lines) visits. The merged image (c) shows that the degree of tilting or sloping of the optic nerve head (ONH) is negligible, while the majority of optic disc change is induced by the elongation of the scleral layer uncovered by the Bruch’s membrane: γ-zone parapapillary atrophy. The ONH tilt angle of initial and final visits were 5.4° and 9.8°, respectively, when measured by the method described in: Marsh-Tootle WL, Harb E, Hou W, Zhang Q, Anderson HA, Weise K, Norton TT, Gwiazda J, Hyman L: Optic Nerve Tilt, Crescent, Ovality, and Torsion in a Multi-Ethnic Cohort of Young Adults With and Without Myopia. Invest Ophthalmol Vis Sci 2017, 58(7):3158–3171