Corneal Topography by Melanie Corbett & Nicholas Maycock & Emanuel Rosen & David O’Brart

Author:Melanie Corbett & Nicholas Maycock & Emanuel Rosen & David O’Brart
Language: eng
Format: epub
ISBN: 9783030106966
Publisher: Springer International Publishing

Topographic Features

In keratoconus, the thinning most commonly occurs just inferior to the corneal centre. Protrusion in this region gives the corneal surface an exaggerated prolate shape. The point of maximum protrusion is termed the apex of the cone. It is the highest point of the cornea and therefore has a slope of zero (in the same way as the very top of a hill is horizontal). The points of maximum steepness and greatest power (or smallest radius of curvature) are usually both inferior to the apex (Fig. 10.1). This results in astigmatism, which is asymmetric between the upper and lower hemispheres of the cornea.

Fig. 10.1Structure of a cone . The apex of the cone in keratoconus is at the highest point of the cornea and can therefore only be located from height or slope maps. The circles represent the relative radius of curvature of different parts of the cornea. For eccentric cones , the smallest radius of curvature (greatest power) is peripheral to the apex. The region of steepest slope may be even more peripheral. Therefore it is important to appreciate which scale is used in any map studied

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