Cup-to-disc ratio

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Measurement used in ophthalmology to assess the progression of glaucoma. The optic disc is the anatomical location of the eye's "blind spot", the area where the optic nerve and blood vessels enter the retina. The optic disc can be flat or it can have a certain amount of normal cupping. But glaucoma, which is due to an increase in intra-ocular pressure, produces additional pathological cupping of the optic disc.

The cup-to-disc ratio compares the diameter of the "cup" portion of the optic disc with the total diameter of the optic disc. A good anology to better understand the cup to disc ratio is the ratio of a donut hole to a donut. The hole represents the cup and the surrounding area the disc. If the cup fills 1/10 of the disc, the ratio will be 0.1. If it fills 7/10 then the ratio is 0.7. A large cup-to-disc ratio may imply glaucoma or other pathology. [1] However, cupping by itself is not indicative of glaucoma. Rather, it is an increase in cupping as the patient ages that is an indicator for glaucoma. Deep but stable cupping can occur due to hereditary factors without glaucoma.

The pink rim of disc contains nerve fibers. The white cup is a pit with no nerve fibers. As glaucoma advances, the cup enlarges until it occupies most of the disc area. Courtesy AgingEye Times