Comparison of Cross-cylinder and Conventional Photorefractive Keratectomy(PRK) in Correcting Medium-high Astigmatism

Comparison of Cross-cylinder and Conventional PRK for Laser Correction of Astigmatism: A Randomized Clinical Trial.

The purpose of this study is to determine whether cross-cylinder approach is more effective than routine method in laser correction of astigmatism.

Both eyes of 50 patients(100 eyes) with medium-high compound myopic astigmatism and inclusion criteria,will be treated by photorefractive keratectomy (PRK) using excimer laser.It breaks chemical bonds within corneal stroma.It's wavelength is 193 nm that is in the ultraviolets range with high energy and very low tissue penetrance. The right or left eye of every patient would be allocated randomly to one of the study groups using RandList 1.1. In spite of recent advances in excimer laser machines and surgical techniques,correction of astigmatism is not more successful compared to myopia. In this study we will compare two methods of laser correction of astigmatism regarding to visual acuity,residual error and aberrations.

Inclusion Criteria:

• >20 years of age
• refractive stability for at least one year
• regular and symmetric astigmatism of >1.5 diopters

Exclusion Criteria:

• corneal thickness<470 microns
• keratoconus or suspected keratoconus
• active ocular disease and systemic collagen disease