Table 1.

Optic nerve variables systematically analyzed.

Variable		Definition/Criteria of analysis
Disc-to-macula distance (DM) to disc diameter (DD) ratio (DM/DD)		DM/DD indicates the number of optic discs that can be apposed between the fovea and the center of the disc (29). Figure 1A shows how DM/DD was calculated.
Double ring sign		An outer ring formed by the area composed of bare sclera and an inner ring formed by the retinal nerve fibers (30)
Physiological cupping		Presence or absence
Cup-to-disc ratio		Horizontal cup diameter-to-horizontal disc diameter ratio
Optic disc ovality		Vertical-to-horizontal disc diameter ratio (or the maximal-to-minimal disc diameter ratio if the vertical diameter was oblique) (31). Oval discs were defined as having an ovality ratio >1.33
Torted optic disc		Deviation of the long axis >15°From the vertical meridian (32)
Peripapillary crescents		Presence or absence
Peripapillary crescentsa	Scleral crescent	If the sclera was visible in the crescent while the choroid and the pigment epithelium did not reach the optic disc margin (33)
	Choroidal crescent	If the choroid was visible in the crescent, as only the pigment epithelium did not reach the optic disc margin (34).
Peripapillary crescents localization		Temporal Below the disc (if the wider area of the crescent was inferiorly located) Annular (if the crescent was present in at least three quadrants), Other (for all other localizations).
Peripapillary atrophy		Atrophy is recognized by less well-defined contour compared to crescents, and variable degrees of extension.
Intra and peripapillary pigment anomalies	Gray crescents	An extension of the retinal pigment epithelium and Bruch membrane within the peripheral tissue of the optic disc (35).
	Conus pigmentosumb	Dark pigmented zone, resulting from localized proliferation of retinal pigment epithelium (36).
	Intrapapillary pigment	Papillary involvement of uveal melanocytes (37)
Tilted discc		If the optic nerve head was tilted in its sagittal axis.
Color		Graded as normal, temporal pallor or overall pallor.
Contour		Graded as sharp or elevated.

Definition and criteria of analysis.

^aBoth crescents are sharply boarded, and they were differentiated on photographic images because the scleral crescent was whitish and the choroidal was gray.

^bThe conus pigmentosum was differentiated from the choroidal crescent as it was more darkly pigmented, usually with a less well-defined contour and various shapes.

^cThe fundus image was corroborated by ophthalmoscopic examination to allow a better three-dimensional visualization of the optic nerve head insertion in confirming the tilted disc.