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Corneal topography: principles and applications

The topography is a geography term which comes from the Greek "topos" (the place) and "graphein" (describe). Corneal topography is the graphical representation of some geometric properties of the corneal surface. The measure of relief, the curvature, and the thickness of the cornea are crucial steps in the diagnosis and screening of corneal diseases, as well as the development of methods of vision correction.

The corneal topographer is a measuring instrument that performs a mapping specialist of the cornea, the anterior transparent window of the eye.

The modeling of the cornea appealed to special geometric considerations. It is necessary denconnaitre frustrates these properties to better interpret the maps of corneal topography and design sensitive and specific screening tests for the screening of Keratoconus.

 

The geometry of the cornea can be studied according to various technologies, which generally provide complementary data. Instruments that measure and describe more accurately the topographic corneal surface properties can be classified into two main types:

-the Placido disk (which uses concentric reflective test patterns)

-the elevation/depression recorders (using a device to scan a line of light either, a rotating Scheimpflug camera, or of a Stereography by frame - "raster-topography").

Topographic curvature systems based on Placido disk are valuable tools in assessing the curvature and the corneal refraction, but they do not directly describe the actual spatial form of the cornea. The elevation topographers provide a direct estimate of the elevation of the cornea, thus establishing a 'real' map three-dimensional shape of the anterior and posterior corneal surface. The topography of curvature and combined elevation has a great potential in the corneal anomaly detection, adaptation of contact lenses and refractive surgery planning.

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