The Performance of Four Different Corneal Topographers on Normal Human Corneas and Its Impact on Orthokeratology Lens Fitting

Purpose. To evaluate the performances of Humphrey Atlas 991, Orbscan II, Dicon CT200, Medmont E300 on young Chinese adults. Methods. Three sets of corneal topography measurements were obtained from each topographer from 22 subjects—two sets by the same examiner and one set by another examiner on the same day. Results. There were no significant within-examiner and between-examiner differences for any of the parameters tested for each topographer. However, only the repeatability and reproducibility (of apical radius[Ro], eccentricity, and elevation) of the Humphrey and Medmont were good. There was no statistically significant between-topographer difference in Ro, but significant differences in eccentricity and elevation values were found. The number of repeated readings that should be taken for a precision of 2 &mgr;m (elevation) were 12 for the Humphrey and 2 for the Medmont. Conclusions. The performance of both the Humphrey and the Medmont was very good. Roand eccentricity values of different topographers cannot be used interchangeably, but the agreement in elevation values was good for these topographers. The number of repeated readings required for maximum precision varies with the topographer used, and they are not interchangeable.

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