الفهرس 
Optical Concepts Of KeratoscopyOnly 14 pages are availabe for public view
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Abstract
The anterior surface of the cornea is the major refractive surface of the eye, responsible for more than two-thirds of its total refractive power. Therefore, minimal changes in corneal topography dramatically affect the clearness of the image focused on the retina.
Clinicians have a number of methods for measuring corneal power and/or corneal shape including keratometry, keratoscopy, photokeratography, interferometry, computer assisted videokeratography, and rasterstereography. The Orbscan corneal topography system is a new device used to evaluate topography of the anterior and posterior corneal surfaces simultaneously. It provides both anterior and posterior corneal elevation maps , pachymetry as well as axial power data. Some corneal diseases,for example, posterior keratoconus, could only be diagnosed by evaluating the shape of the posterior corneal surface.
The aim of this work is to study corneal topography in normal Egyptian eyes using Orbscan corneal topography system.
In our study we evaluate 100 eyes of normal candidates and we found that the most common pattern in anterior elevation maps was the island 64%, the most common pattern in posterior elevation maps was the incomplete ridge 47%, the most common axial power map was asymmetrical bow tie 34% and the most common pachymetric pattern was round 48% . The central corneal thickness was 551.4µm (± 30.3) and the thinnest site on the entire cornea was an average of 539.4 µm(±32) ,commonly located in the inferotemporal quadrant.
We recommend the followings:
Special attention should be paid to the posterior surface of the cornea as sub clinical cases of posterior keratoconus may be detected by Orbscan which is a good device for corneal topography evaluation.
There are racial differences in corneal topography patterns which need further studies.
In conclusion, the results of this study provide a helpful reference for standards of Egyptian normal eyes as regards elevation, keratometric and corneal thickness using the Orbscan corneal topography system. These data will hopefully prove useful for future comparative studies.