الفهرس 
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Abstract
Introduction: Keratoconus is non inflammatory, ectatic corneal disorder characterized by progressive corneal thinning that results in corneal protrusion, irregular astigmatism, and decreased visual acuity. The incidence of keratoconus is about 1 of 2,000 individuals with a higher incidence in refractive surgery candidates.
Aim: To determine the changes of posterior corneal astigmatism in cases with keratoconus.
Patients and methods: One hundred eyes of fifty patients were included in this retrospective, case control study which adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committees of the Ain Shams University Hospitals. These cases were divided into: Keratoconus group: comprised 50 eyes of 25 patients with keratoconus diagnosed on the basis of clinical and topographic signs. Control group comprised 50 eyes of 25 normal candidates for refractive surgery
Results: A total 100 cases were included in this retrospective study with mean age of 30.01 ±8.19 years old. The females were predominant in 63%.These cases were divided into keratoconus & control groups, each one had 50 cases. The mean age of keratoconus group was 29.39 ±7.81 years old versus 30.52±8.53 years old in control group. Females were predominant in keratoconus group (52%) while males were predominant in control group (54%).
Conclusion: We found that PCA is more increased in KC and its increase is correlated to anterior corneal astigmatism and CK1 but inversely correlated to Q values of both front and back corneal surfaces.
Recommendations: We recommend to routinely use pentacam or schimflug imaging device for refractive candidates as well as in diagnosis of KC.
Posterior corneal surface parameters are more important in detecting early or susceptible ectasia especially posterior corneal astigmatism, posterior Q value and posterior elevation point at thinnest location.