Keratoconus is a bilateral (but usually asymmetrical) non-inflammatory progressive thinning process of the cornea. It manifests as characteristic cone-like ectasia of the cornea associated with irregular stromal thinning, resulting in a cone-like bulge , which causing irregular astigmatism and vision impairment.

Keratoconus is the most common form of corneal ectasia, with an incidence of 50-230 per 100,000 persons.Pentacam used diagnose & detect the progression in patients with keratoconus and also provide a detailed information about corneal tomography and topography.

In the last few years, it has been shown that in healthy individuals the posterior corneal surface has not only a different amount of astigmatism but also a different alignment of the steep meridian.

The aim of this research is to compare the amount and axis alignment of anterior and posterior corneal astigmatism in keratoconus with a healthy controlled group .

Inclusion Criteria:

• Patients diagnosed with keratoconus using the following criteria:

Specific diagnostic signs is asymmetric refractive errors with high progressive or irregular astigmatism, and elevated keratometry values, scissoring of the red reflex, Vogt striae, Fleischer rings, inferior or central steepening on topography with abnormal localized steepening .

Exclusion Criteria:

• Unwillingness to participate in the study .
• Corneal scarring.
• Any ectatic conditions that were not explicitly keratoconus such as keratoglobus and pellucid marginal degeneration .
• Previous ocular surgery.