Fig. 2

Measuring the parameters of myopic tilted disc: the ovality index, optic disc torsion, and optical coherence tomography (OCT) horizontal tilt angle. a The ovality index was determined by the ratio (a:b) of the longest diameter (arrow a) and the shortest diameter (arrow b) of the optic disc identified on the fundus photograph. The optic disc torsion angle was defined as the angle between the axis along the longest diameter of the optic disc (arrow a) and the vertical median (white line) that was perpendicular to the Disc-Fovea line (black dot line) connecting the center of the optic disc and the fovea. b The triple overlayed image consisted of an optic disc color photograph, the en-face swept-source OCT (SS-OCT) image, and the horizontal cross-sectional scan of the optic disc. According to the green line that crosses the optic disc, the clinical boundary of the optic disc was identified, with two white lines drawn across the clinical boundary and extended down to mark the corresponding optic disc border in the cross-sectional OCT scan. The white dots indicate the clinical boundary of the optic disc, and the two blue dots indicate the inner edges of the Bruch’s membrane. The OCT tilt angle was the angle between the connecting line of Bruch’s membrane border (blue line) and connecting line of the disc boundary (white dot line)