Compare corneal high order aberrations before and after stream light trans-PRK and mechanical photorefractive keratectomy including third order aberrations; Trefoil and coma aberrations and forth order aberrations; spherical aberrations

Laser technology has played an important role in promoting the development of ophthalmology, especially corneal refractive surgery.1 Trans-epithelial photorefractive keratectomy (Trans-PRK) has become a highly researched topic in recent years.2 Different epithelial debridement methods with PRK showed favorable results for the surgical treatment of low to moderate myopia3. In mechanical PRK (m-PRK), epithelial debridement is achieved using a blunt spatula, whereas in stream light trans-PRK (t-PRK), there after an excimer laser is used to ablate corneal stroma3. The Stream Light t-PRK is a safe and effective treatment option for the correction of low to moderate myopia.4 Many studies have shown that the corneal asphericity developed significantly after refractive surgeries and introduce higher-order aberrations (HOAs).2 The present study focused on three of the most clinically important HOAs; spherical, coma, and trefoil aberrations, both preoperative and postoperative were recorded from topography over the 6-mm-diameter central corneal zone using Pentacam.

Inclusion Criteria:

• • Stable refraction for 1 year (refraction does not exceed 1D more than the last prescribed glasses).

  • Discontinuation of soft contact lens wears at least 1 week before examination.
  • Topography criteria:

• Corneal thickness equal or more than 470 um

• Symmetrical bow-tie

• Back elevation not more than +12

• Normal Belin\Ambrosio Enhanced ectasia display

• Spherical equivalent not more than -6D.

Exclusion Criteria:

• • Previous ocular surgery

  • Concurrent ocular pathology; corneal scar, corneal dystrophy
  • Systemic disease; Uncontrolled diabetes, collagen disease
  • Post-operative complications; sub-epithelial haze.

Myopic patients with spherical equivalent not more than -6D who will present to refractive surgery Centre in Assiut and seeking for refractive surgery to get rid of their glasses and fulfilling the inclusion and exclusion criteria