Codeine Plus Paracetamol Versus Placebo for PRK Post-operative Pain

Inclusion Criteria: * older than 20 years * spherical component between -1.00 and -5.00, with or without astigmatism * cylindrical component up to 1.5D * spherical anisometropia of less than or equal to 0.75D, * cylindrical anisometropia of less than or equal to 0.5D, * stable refraction errors (maximal variation of 0.5D in the spherical or cylindrical component during 1 year) * amenable to follow-up for at least seven (7) days. Exclusion Criteria: * presence of active disease of allergic, inflammatory or infectious nature, in the ocular surface or its attachments * previous ocular history (pathology, surgery or ocular trauma) * best corrected visual acuity less than 20/25) * autoimmune disease, or immunosuppression or Diabetes Mellitus * pregnancy or lactation.