29-06-2017, 03:57 PM
The ratio between cup and disc (often CDR) is a measure used in ophthalmology and optometry to evaluate the progression of glaucoma. The optic disc is the anatomical location of the "blind spot" of the eye, the area where the optic nerve and blood vessels enter the retina. The optical disk may be flat or may have a certain amount of normal suction cups. However, glaucoma, which in most cases is associated with increased intraocular pressure, often produces additional pathologic ventricles of the optic disc. The pink edge of the disc contains nerve fibers. The white cup is a pit with no nerve fibers. As glaucoma progresses, the cup enlarges to occupy most of the area of the disc.
The cup-to-disk ratio compares the diameter of the "cup" portion of the optical disk to the total diameter of the optical disk. A good analogy to better understand the cup-to-disk ratio is the ratio of a donut hole to a donut. The hole represents the cup and the area surrounding the disc. If the cup full 1/10 of the disk, the ratio will be 0.1. If it fills 7/10 of the disk, the ratio is 0.7. The normal cup-to-disk ratio is 0.3. A large cup-to-disc ratio may involve glaucoma or other pathology. However, cupping by itself is not indicative of glaucoma. On the contrary, it is an increase in suction cup when the patient ages which is an indicator for glaucoma. Deep but stable cupping may occur due to hereditary factors without glaucoma.