title: Three and Four Horizontal Muscle Surgery for Large Angle Exotropia.
abstract: OBJECTIVE
  Surgery on two horizontal recti typically is most effective for angles less than 40 prism diopters (PD). The authors evaluate their experience operating on three or four rectus muscles for angles exceeding 40 PD.
  
  
  METHODS
  Retrospective chart review of 47 patients who underwent a first surgical procedure for a large angle comitant exodeviation. Patients were observed for a minimum of 2 months. Success was defined as deviation ±10 PD.
  
  
  RESULTS
  Median age was 48 years (range: 1 to 79 years). Thirty-four patients underwent three muscle surgery and 13 underwent four muscle surgery. Mean preoperative angles were 55 ± 9.8 and 72 ± 8.8 PD, respectively. Following three muscle surgery, rates of success, undercorrection, and overcorrection were 67%, 27%, and 7% at 2 months and 42%, 58%, and 0% at final follow-up (12 ± 8.7 months), respectively. Rates for four muscle surgery were 44%, 33%, and 22% at 2 months and 50%, 38%, and 13% at final follow-up (11 ± 12.2 months), respectively. Patients who were successfully aligned at 2 months had a mean preoperative angle of 55 PD, whereas those who were undercorrected had a mean preoperative angle of 67 PD (P = .009). Between 1 week and 2 months, 77% of patients experienced exotropic drift averaging 10 ± 9.1 PD. By final follow-up, 90% experienced exotropic drift averaging 15 ± 14.1 PD. Success rates for traditional and adjustable suture surgeries did not differ significantly.
  
  
  CONCLUSIONS
  Three and four horizontal muscle surgeries are effective for correcting large angle exotropia. Higher preoperative deviations predisposed to undercorrection. Postoperative exotropic drift should be anticipated.
authors.forename: John H
authors.initials: JH
authors.lastname: Chen
authors.forename: David G
authors.initials: DG
authors.lastname: Morrison
authors.forename: Sean P
authors.initials: SP
authors.lastname: Donahue
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005099:Exotropia / Q000503:physiopathology / Q000601:surgery*; D005133:Eye Movements / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000601:surgery*; D013508:Ophthalmologic Surgical Procedures; D012189:Retrospective Studies; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology