What is Cup-to-Disc Ratio (CDR)? - Glaucoma Glossary

The cup-to-disc ratio is a structural measurement used by eye care professionals to assess the progression of glaucoma, comparing the diameter of the optic cup to the total diameter of the optic disc.

What it means for the patient

Your optic nerve has an outer rim (the disc) and an inner hollow area (the cup). In glaucoma, the nerve fibers in the rim die off, causing the hollow cup to become larger. A higher ratio often indicates more severe glaucoma.

Clinical significance

An increasing CDR, particularly vertical cupping or focal notching (such as the inferior rim), is a highly specific structural hallmark of glaucomatous optic neuropathy that precedes detectable functional visual loss.

How it is tracked

CDR evolution is structurally quantified using Optical Coherence Tomography (OCT) automated progression analysis and cataloged in the clinical timeline.