Apr 07, 2010
"cupping" is a term applied to the optic nerve on the back of the eye. The optic nerve generally has a "dimple" or "cup". Ophthalmologists use a ratio called the cup to disk ration "C/D ration". An estimate is made of the width of the cup to the width of the whole optic serve. It is usually expressed as a decimal tenth. A flat optic nerve with no cup would be C/D = .0 an optic nerve ravaged by glaucoma that is 'cupped out" would be C/D = 1.0 So the possibilies are: 0, .1,.2,.3.,.4,.5,.6,.7,.8,.9,1.0 Some physicians express two numbers one being the verticle C/D and the other being the horizontal C/D. It has been shown that these are not exact numbers. There are large variations from observer to observer and even from the same observer from visit to visit.
90% of the population without glaucoma have C/D ratios of .4 or less. So a larger C/D might indicate glaucoma. However it's very complicated. You can have glaucoma with a small C/D and not have glaucoma with a large C/D. Other factors need to be taken into account like family history of glaucoma, age, corneal thinness, intra ocular pressure (remeber you IOP varies from hour to hour just like your blood pressure and your blood sugars. Many patients with glaucoma have normal IOPs for some or even most of a 24 hour period, conversely patients without glaucoma may top out over 21 for part of the day). Another factor is if the C/D are different in each eye, usually they're the same size.
When I see a patient with a C/D ratio or .5 or more I always tell them and explain what it means so that the next ophthalmologist that examines the patient will know it's been noted before.
I would never tell a person they had "moderate cupping" without explaining what it meant and giving them "the number" to add to their medical records. Sometimes I'll take a photograph of the optic nerves as a baseline. A new and wonderful instrument the OCT (optical coherence tomography) instrument has taken a lot of the guessing out of these issues and if there's any question at all that's the test I go to.