An elevation in the ratio of the diameter of the cup of the optic disc to the total diameter of the disk. The optic disc has an orange-pink rim with a pale center (the cup) that does not contain neuroretinal tissue. An increase in this ratio therefore may indicate a decrease in the quantity of healthy neuroretinal cells. [https://orcid.org/0000-0002-0736-9199, PMID:23557744]