cuptodisc

Cuptodisc is a term used in ophthalmology to describe the cup-to-disc ratio (CDR), a metric that compares the size of the optic cup to the overall optic disc. The optic disc is the visible entry point of the retinal nerve fibers where the optic nerve exits the eye, and the optic cup is a central depression within the disc. The cup-to-disc ratio is commonly expressed as a vertical measurement, since cupping tends to be more pronounced in the vertical axis.

Clinical use and interpretation

The CDR is used to assess glaucomatous damage and to monitor changes in the optic nerve over time. A higher CDR can indicate excavation of the optic nerve head associated with glaucoma or other optic neuropathies, while a lower CDR is typical in healthy eyes. Normal values vary between individuals and depend on optic disc size; larger discs can have larger cupping without disease, whereas small discs may show significant cupping with disease. Because of this variability, the CDR is interpreted in the context of disc size, intraocular pressure, visual field testing, and other imaging data.

Measurement and methods

CDR can be estimated during a dilated fundus examination, or more precisely measured using fundus photography, optical coherence tomography (OCT), or confocal scanning laser ophthalmoscopy. In addition to the vertical CDR, clinicians may consider the overall cup-to-disc area ratio and other quantitative metrics of the neuroretinal rim.

Limitations

CDR assessment can be influenced by observer judgment, image quality, and anatomical factors such as myopia or disc size. It is most informative when used to detect progression over time rather than as a stand-alone diagnostic test.