title: A new index to measure the accuracy of refractive operations.
abstract: OBJECTIVE
  To create a new index to help evaluate the accuracy of the outcome of refractive surgery.
  
  
  METHODS
  By combining information given by the cross-cylinder form of surgically induced refractive change (SIRC) and basic methods of vector analysis, we constructed a new index which serves as a tool to evaluate postoperatively the changes achieved by refractive surgery. This new index gives easily understandable numerical values and takes into account changes in both spherical refraction and astigmatism. We demonstrated the use of this index in two study populations consisting of 20 consecutive eyes operated on using two different lasers, Meditec MEL60 and MEL70, respectively.
  
  
  RESULTS
  Although postoperative uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) were better in the MEL70 group, the difference of photoefractive keratectomy (PRK) for combined astigmatism and myopia was not statistically significant. Comparison of the changes in refraction achieved by the two lasers indicated that the MEL60 was more accurate; this was also seen when comparing the total index of error between the two groups.
  
  
  CONCLUSIONS
  We suggest the use of this total index of error (TIE) in clinical praxis because it provides an easy and accurate method of evaluating the accuracy of refractive operations. These inaccuracies might otherwise go unnoticed if the basic values only (e.g. UCVA, BCVA and haze) were used in postoperative evaluation.
authors.affiliation: Department of Ophthalmology, University of Tampere, Medical School, 33100 Tampere, Finland. sakari.suominen@uta.fi
authors.forename: S
authors.initials: S
authors.lastname: Suominen
authors.forename: J
authors.initials: J
authors.lastname: Pietilä
authors.forename: P
authors.initials: P
authors.lastname: Mäkinen
authors.forename: H
authors.initials: H
authors.lastname: Uusitalo
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000592:standards*; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D014792:Visual Acuity