title: Muscular asthenopia and eccentric ablation after photorefractive keratectomy.
abstract: OBJECTIVE
  To investigate the relationship between muscular asthenopia and eccentric ablation after photorefractive keratectomy (PRK).
  
  
  METHODS
  Sixteen eyes of eight myopic patients whose muscular asthenopia was corrected by subjectively accepted spectacle prism after PRK, with visual acuity better than 0.8, were followed for 6 to 14 months. On the basis of preoperative and post-operative data and corneal topography, we calculated the total corrected corneal power using the Holladay formula and then measured the ablation eccentricity (h, millimeters) and its direction. According to the formula delta approximately equals Dh, the prism effective value (delta) caused by the eccentric ablation was computed and compared with the objectively accepted spectacle prism.
  
  
  RESULTS
  The subjectively accepted spectacle prisms were similar to calculated values from the formula. Mean difference was 0.10 +/- 0.25delta. The direction of the subjectively accepted prism was in the direction of the ablation deviation.
  
  
  CONCLUSIONS
  Eccentric ablation is an important cause of muscular visual asthenopia after PRK. The asthenopia may be corrected by spectacle prism. The spectacle prism value may be estimated by the formula delta approximately equals Dh.
authors.affiliation: Institute of Ophthalmology, Shandong Academy of Medical Science, Qingdao, People's Republic of China.
authors.forename: G
authors.initials: G
authors.lastname: Wu
authors.forename: L
authors.initials: L
authors.lastname: Xie
authors.forename: Z
authors.initials: Z
authors.lastname: Yao
mesh_terms: D000328:Adult; D001248:Asthenopia / Q000209:etiology* / Q000628:therapy; D001251:Astigmatism / Q000209:etiology* / Q000628:therapy; D003315:Cornea / Q000601:surgery; D019781:Corneal Topography; D004172:Diplopia / Q000209:etiology / Q000628:therapy; D005139:Eyeglasses; D006801:Humans; D054018:Lasers, Excimer; D009216:Myopia / Q000601:surgery; D018903:Photorefractive Keratectomy / Q000009:adverse effects*; D014792:Visual Acuity