cup/disk ratio (C/D, CDR)

Introduction

Finding on ophthalmoscopy:

Ratio of cup to optic disk.

Normal ratio is 0.3

Pathology

• an increased ratio (> 0.6) is characteristic of glaucoma.

Notes

• the optic disk can have a certain amount of cupping, a white cup or pit within the optic disk that contains no nerve fibers
• it is actually the increase in cupping that is indicative of glaucoma
• deep but stable cupping can occur due to hereditary factors without glaucoma

Additional terms

• glaucoma
• ophthalmoscopy
• optic disk cupping