title: Astigmatism induced by simultaneous recession of both horizontal rectus muscles.
abstract: OBJECTIVE
  Changes have been reported in the refractive state of the eye after various types of strabismus surgery. This study investigates the effect of large simultaneous recession of both horizontal rectus muscles on the refractive state of the eye.
  
  
  METHODS
  Twenty-six eyes (13 patients) were refracted 1 to 2 weeks before and 6 to 8 weeks after large horizontal rectus muscle recessions for the purpose of damping nystagmus. The preoperative refraction was mathematically subtracted from the postoperative refraction, and the induced refractive changes were averaged and statistically analyzed. The relation between the amount of recession and the induced astigmatism was also investigated.
  
  
  RESULTS
  A statistically significant change in astigmatism in the with-the-rule direction was induced with this procedure (+ 0.70 diopter cylinder, axis 90.0 degrees, P <.0002). With the narrow range of amounts of recession performed, there was no demonstrable relation between the amount of recession and the amount of induced astigmatism.
  
  
  CONCLUSIONS
  Recession of both horizontal rectus muscles, the same as has been reported for recession of one horizontal rectus muscle and recession-resection surgery on both horizontal rectus muscles, tends to induce a change in astigmatism in the with-the-rule direction.
authors.affiliation: Department of Ophthalmology, Labbafinejad Hospital, Shahid Beheshti University, Tehran, Iran.
authors.forename: Abbas
authors.initials: A
authors.lastname: Bagheri
authors.forename: Azadeh
authors.initials: A
authors.lastname: Farahi
authors.forename: David L
authors.initials: DL
authors.lastname: Guyton
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000209:etiology* / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D009759:Nystagmus, Pathologic / Q000601:surgery*; D009801:Oculomotor Muscles / Q000601:surgery*; D013508:Ophthalmologic Surgical Procedures / Q000009:adverse effects*; D011446:Prospective Studies