CHARACTERISTICS OF NORMAL CORNEAL TOPOGRAPHY USING THE EYESYS CORNEALANALYSIS SYSTEM

Purpose: To study the parameters of corneal topography of normal eyes using the Corneal Analysis System (GAS, EyeSys Technologies) to determ ine the types and frequency of patterns and parameters. Setting: Unive rsity of Illinois Eye Center, Chicago, Illinois, USA. Methods: Three i ndependent, masked judges, using a forced-choice paradigm, classified corneal topography patterns into six categories on one randomly select ed, normal eye of 100 persons who did not wear contact lenses. The pat terns were defined by using the midpoint dioptric bin and a 0.50 diopt er (D) steeper bin. Results: The pattern frequency using the mid-diopt ric bin was teardrop (6%), amorphous (11%), round (11%), symmetric bow tie (17%), asymmetric bow tie (1%), kidney (22%), and oval (32%). Mea n 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%), asymmet ric bow tie (17%), and symmetric bow tie (37%). Mean refractive and ke ratometric cylinders, respectively, were round (0.13 and 0.32 D), amor phous (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 f lat 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. M ean contour range was 2.40 D (95% CI, 0.61 to 4.17 D).Conclusion: 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 l ess than 4.25 D when using the EyeSys CAS.