title: Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation.
abstract: OBJECTIVE
  To assess the efficacy and safety of a combined ablation of the steep and flat meridian to correct astigmatism with the excimer laser.
  
  
  METHODS
  Twenty-two eyes with myopic, mixed, or hyperopic astigmatism (mean preoperative spherical equivalent refraction -4.30 +/- 4.70 D [range, -12.50 to +1.50 D] and mean preoperative cylinder magnitude -3.40 +/- 1.40 D [range, -1.50 to -6.00 D]) underwent PRK with the Nidek EC-5000 excimer laser. The surgical strategy involved ablating half the amount of the cylinder (in diopters) along steepest meridian, the other half in a subsequent step along the flattest meridian; thereafter, the spherical equivalent was corrected.
  
  
  RESULTS
  Six months postoperatively, mean spherical equivalent refraction was -0.07 +/- 0.87 D and mean cylinder was -0.44 +/- 0.36 D. Mean spectacle-corrected visual acuity was 0.86 +/- 0.13 compared to 0.75 +/- 0.22 preoperatively. Mean corneal haze was 0.67 +/- 0.31. No patient lost 2 or more lines of spectacle-corrected visual acuity and there were no complaints about night halos or glare.
  
  
  CONCLUSIONS
  Unlike other ablation strategies, the cross-cylinder method creates a smooth transition (low dioptric gradient) between the treated and untreated cornea. This is achieved by first treating the cylinder and making the corneal surface spherical and then ablating the spherical component of the refractive error.
authors: Department of Ophthalmology, San Gerardo Hospital, Monza, Italy.
authors: P
authors: P
authors: Vinciguerra
authors: M
authors: M
authors: Sborgia
authors: D
authors: D
authors: Epstein
authors: M
authors: M
authors: Azzolini
authors: S
authors: S
authors: MacRae
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000150:complications / Q000601:surgery*; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D006956:Hyperopia / Q000150:complications / Q000601:surgery*; D054018:Lasers, Excimer; D008875:Middle Aged; D009216:Myopia / Q000150:complications / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000379:methods*; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D012449:Safety; D016896:Treatment Outcome; D014792:Visual Acuity