title: Reliability of Orbscan II topography measurements in relation to refractive status.
abstract: OBJECTIVE
  To investigate the reliability of corneal topography measurements using the Orbscan II topography system (Bausch & Lomb) not only referring to a normal cohort but also to different refractive conditions.
  
  
  METHODS
  Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany.
  
  
  METHODS
  Eighty patients (mean age 46.4 +/- 19.0 years) were assigned to 4 refractive groups (Group A: emmetropia (n=20); Group B: astigmatism (n=20) (-1.98 +/- 1.77 diopters [D]); Group C: hyperopia (n=20) (+4.84 +/- 1.6 D); Group D: myopia (n=20) (-9.64 +/- 3.79 D). Three measurements were performed in a series. Thirteen defined, standardized points of the entire cornea (apex, 3.0 mm, 5.0 mm, and 7.0 mm zone) were evaluated for 3 different maps (anterior elevation, pachymetry, keratometry).
  
  
  RESULTS
  In all 80 patients, the following mean values were found in relation to analyzed zones: with regard to the anterior elevation map, the values decreased from 5.53 microm (center) to -6.52 microm (7.0 mm zone), the corneal thickness increased from 549.41 microm to 638.63 microm peripheral and the keratometry from 43.86 D (apex) to 45.4 D (7.0 mm zone), respectively. Analysis of the 3 different maps in all 4 refraction groups showed a tendency toward an increase in SD from the center to the 7.0 mm zone for anterior elevation and pachymetry maps. For keratometry, however, the lowest SD was found in the 7.0 mm zone. In particular, patients with hyperopia showed significant differences (P<.01), compared with emmetropic patients; the SD was higher with regard to anterior elevation as well as keratometry in peripheral zones. Group B (astigmatism) showed significantly higher SD for anterior elevation in zones 3.0, 5.0, and 7.0 mm when compared with emmetropic patients.
  
  
  CONCLUSIONS
  The repeated Orbscan II measurements showed SD in the micrometer range for anterior elevation and pachymetry but values between 0.48 D and 0.97 D for keratometric data. Patients with astigmatism and especially hyperopia showed significantly higher SD values in peripheral zones for anterior elevation and keratometry, indicating a lower reliability, compared with the emmetropic cohort. However, the different ages of the patients could also be a possible explanation for these findings. Therefore, the Orbscan II seems to be a predictable and useful device for measuring corneal topography.
authors.affiliation: Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany.
authors.forename: Tanja M
authors.initials: TM
authors.lastname: Rabsilber
authors.forename: Klio A
authors.initials: KA
authors.lastname: Becker
authors.forename: Gerd U
authors.initials: GU
authors.lastname: Auffarth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results