title: Characteristics of normal corneal topography using the EyeSys corneal analysis system.
abstract: OBJECTIVE
  To study the parameters of corneal topography of normal eyes using the Corneal Analysis System (CAS, EyeSys Technologies) to determine the types and frequency of patterns and parameters.
  
  
  METHODS
  University of Illinois Eye Center, Chicago, Illinois, USA.
  
  
  METHODS
  Three independent, masked judges, using a forced-choice paradigm, classified corneal topography patterns into six categories on one randomly selected, normal eye of 100 persons who did not wear contact lenses. The patterns were defined by using the midpoint dioptric bin and a 0.50 diopter (D) steeper bin.
  
  
  RESULTS
  The pattern frequency using the mid-dioptric bin was teardrop (6%), amorphous (11%), round (11%), symmetric bow tie (17%), asymmetric bow tie (1 %), kidney (22%), and oval (32%). Mean refractive and keratometric cylinders, respectively, were teardrop (0.13 and 0.15 D), amorphous (0.15 and 0.49 D), round (0.18 and 0.56 D), oval (0.21 and 0.56 D), kidney (0.51 and 0.72 D), and bow tie (1.18 and 1.82 D). Pattern frequency using the 0.50 D steeper bin was round (2%), oval (5%), teardrop (6%), kidney (15%), amorphous (17%), asymmetric bow tie (17%), and symmetric bow tie (37%). Mean refractive and keratometric cylinders, respectively, were round (0.13 and 0.32 D), amorphous (0.25 and 0.38 D), kidney (0.11 and 0.42 D), oval (0.40 and 0.59 D), teardrop (0.08 and 0.75 D), and bow tie (0.65 and 1.09 D). Mean flat and steep contours were 41.76 D (95% confidence interval [CI], 38.68 to 44.84 D) and 44.15 D (95% CI, 41.00 to 47.31 D), respectively. Mean contour range was 2.40 D (95% CI, 0.61 to 4.17 D).
  
  
  CONCLUSIONS
  The data suggest that for 95% of normal corneas, corneal contours will be steeper than 38.50 D, flatter than 47.50 D, and have a contour range less than 4.25 D when using the EyeSys CAS.
authors.affiliation: Department of Ophthalmology and Visual Sciences, College of Medicine, University of Illinois at Chicago, USA.
authors.forename: N P
authors.initials: NP
authors.lastname: Alvi
authors.forename: T T
authors.initials: TT
authors.lastname: McMahon
authors.forename: J
authors.initials: J
authors.lastname: Devulapally
authors.forename: T C
authors.initials: TC
authors.lastname: Chen
authors.forename: M A
authors.initials: MA
authors.lastname: Vianna
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D003315:Cornea / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009885:Ophthalmology / Q000295:instrumentation; D010865:Pilot Projects; D011897:Random Allocation; D012016:Reference Values; D012029:Refraction, Ocular