What is the size of the optic disc?
Structure. The optic disc is placed 3 to 4 mm to the nasal side of the fovea. It is a vertical oval, with average dimensions of 1.76mm horizontally by 1.92mm vertically.
How do you calculate the size of an optic disc?
Probably the most accurate way to manually measure the optic disc is to do high-plus non-contact funduscopy using a 78- or 90-D lens and a slit lamp. To do this, simply bring the disc into view with your high plus lens using a narrow slit lamp beam.
What is normal optic disc area?
Optic disc surface area is between 2.1 mm2 and about 2.8 mm2 (the mean value of 2.69 mm2) with a range from 0.80 mm2 to 5.54 mm2 in an average Caucasian population without high myopia. Optic disc size varies from small to large according to racial heritage as follows: Caucasians, Hispanics, Asians, African-Americans.
What does large optic disc mean?
Large optic discs generally have large optic cups, but they may have a greater number of nerve fibers than small discs. 3 Asymmetry of the cup-to-disc ratio greater than 0.2 or notching or focal or diffuse thinning of the rim of the optic nerve is characteristic of glaucomatous changes.
What is normal C D ratio?
The normal cup to disc ratio (the diameter of the cup divided by the diameter of the whole nerve head or disc) is about 1/3 or 0.3. There is some normal variation here, with some people having almost no cup (thus having 1/10 or 0.1), and others having 4/5ths or 0.8 as a cup to disc ratio.
Is it normal to have a large optic nerve?
When a person is shown to have large optic nerve cups, it could be an indicator of damage unless it can be determined that the cup size is considered normal for that individual. Through periodic photographs of the optic nerve, the ratio of the cup to the disc can be monitored.
How many microns is the optic disc?
1,500 microns
Retinal thickening of one disc area, any part of which is located within one disc diameter (1,500 microns) from the centre of the fovea.
What if your optic nerve is big?