title: Induced astigmatism after 4 and 6 mm scleral tunnel incision. A randomized study.
abstract: OBJECTIVE
  To study the surgically induced astigmatism after phacoemulsification through either a 4 or a 6 mm scleral tunnel incision by using multiple analyses of astigmatism.
  
  
  METHODS
  197 eyes from 186 patients scheduled for phacoemulsification between October 1992 and March 1994 were randomly assigned two different-sized incisions with follow-ups at 1 day, 1 week, 2 weeks, 1 month and 4 months after surgery. The surgically induced astigmatism was evaluated using at each follow-up: 1) The subtraction method, 2) vector analysis, 3) vector decomposition, 4) Cravy's vertical vector, 5) Naeser's polar values, and 6) the algebraic method.
  
  
  RESULTS
  By subtraction, without regard to axis, the induced astigmatism 4 months after surgery was +0.04 D and +0.18 D in the 4 mm and the 6 mm incision group, respectively. By vector analysis, the numerical value of the induced cylinder was stable one month after surgery at 0.61 D and 0.77 D in the 4 mm and in the 6 mm group, respectively. However, cylinder orientation was not found stable until 4 months after surgery, where 94% and 96% of the surgically induced astigmatism (vector decomposition) was against-the-wound in the two groups, respectively. By Cravy's method, the mean induced astigmatism changed from -0.08 D to -0.32 D and from -0.42 D to -0.60 D between 1 and 4 months in the 4 mm and the 6 mm group, respectively. Similar values were found with Naeser's method and with the algebraic method.
  
  
  CONCLUSIONS
  We conclude the mean cylinder of the surgically induced astigmatism (vector analysis) to be stable 1 month after phacoemulsification with both the 4 mm and 6 mm scleral tunnel incision. However, the direction of the induced axis (vector decomposition) was still drifting between 1 and 4 months in both groups. These astigmatic changes were adequately described using vector analysis and vector decomposition.
authors.affiliation: Department of Ophthalmology, Arhus University Hospital, Aarhus C, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Dam-Johansen
authors.forename: T
authors.initials: T
authors.lastname: Olsen
mesh_terms: D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000209:etiology*; D003315:Cornea / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D018918:Phacoemulsification / Q000009:adverse effects* / Q000379:methods; D011183:Postoperative Complications; D012029:Refraction, Ocular; D012189:Retrospective Studies; D012590:Sclera / Q000601:surgery*; D013536:Suture Techniques