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The hole represents the cup and the surrounding area the disc. If the cup fills 1/10 of the disc, the ratio will be 0.1. If it fills 7/10 of the disc, the ratio is 0.7. The normal cup-to-disc ratio is less than 0.5. A large cup-to-disc ratio may imply glaucoma or other pathology. [3] However, cupping by itself is not indicative of glaucoma.
The optic disc is located 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. [2] There is a central depression, of variable size, called the optic cup.
The interpretation of fundus photographs that are glaucomatous must contain a description of the vertical and horizontal cup to disc ratio, vessel pattern, diffuse or focal pallor, asymmetry and development of the above factors. The retinal nerve fibre layer should also be studied and commented on. [23]
Cup–disc ratio CF: Count fingers vision – state distance ... Dissociated vertical deviation EF: ... Normal retinal correspondence NV
In megalopapilla the optic disc diameter exceeds 2.1 mm (or surface area more than 2.5 mm 2 [1]) with an increased cup-to-disc ratio. [2] Although the optic disc is looks abnormal, the disc colour, sharpness of disc margin, rim volume, configuration of blood vessels and intraocular pressure will be normal. [3] [1] Visual field is normal except ...
Changes on ophthalmologic exam include deepening and enlargement of the optic cup (leading to a high cup/disc ratio), a more vertical oval optic cup shape, pallor of the disc, and an increase in the blood vessels within the optic nerve on the nasal side of the disc.
The unit circle is the Cayley absolute that determines a metric on the disk through use of cross-ratio in the style of the Cayley–Klein metric. In the language of differential geometry, the circular arcs perpendicular to the unit circle are geodesics that show the shortest distance between points in the model.
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