الفهرس 
Review of literatureOnly 14 pages are availabe for public view
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Abstract
Keratoconus is an ectatic corneal disorder characterized by progressive corneal thinning that generates a corneal protrusion, irregular astigmatism, and decreased vision. This protrusion, which assumes a conical shape, is generated by degeneration of stromal tissue leading to decrease the mechanical strength of the corneal structure.
Corneal tomography has the ability to measure not only the anterior corneal surface but also the posterior surface, allowing a three-dimensional image of the cornea. This technology provides significantly more information than anterior surface topography, as tomography utilizes data from anterior and posterior surfaces of the cornea, as well as pachymetric mapping.
The importance of posterior corneal astigmatism has been recognized recently, when toric IOL is considered, because selecting toric IOL based on anterior corneal measurements and neglecting posterior corneal astigmatism could lead to an incorrect estimation of total corneal astigmatism.
94 eyes of previously diagnosed Keratoconic patients were included in this study for which corneal topography with rotating Scheimpflug device was done. Evaluation of the magnitude and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA) and the correlation between ACA and PCA in the different stages of keratoconus were studied.
According to axis orientation of ACA and PCA, the dominant type of astigmatism orientation at both anterior and posterior corneal surfaces was WTR, some were oblique and there were no cases with ATR astigmatism orientation.
The magnitude of K1, K2, Mean K, ACA, anterior elevation and posterior elevation showed a highly statistically significant increase as the stages of KC progressed. The magnitude of PCA showed a statistically significant difference between the four groups.
There was a highly statistically significant correlation between ACA&PCA and anterior & posterior elevation in the different stages of KC.
There was a statistically significant correlation between TL & PCA in the different stages of KC and there was no correlation between TL-Y coordinate &PCA in the different stages of KC.