COMPARISON OF 3 COMPUTERIZED VIDEOKERATOSCOPY SYSTEMS WITH KERATOMETRY

Purpose: To compare the reproducibility of computerized videokeratosco py systems by using normal eyes and calibrated objects. Methods. We ev aluated the reproducibility of three commercially available videokerat oscopes [EyeSys, TechnoMed C-Scan, and PAR Corneal Topography System ( CTS)I with the manual keratometer (Bausch & Lomb) by using calibration spheres and 10 normal subjects (20 eyes). All videokeratoscopy and ke ratometer results were obtained by one investigator (R.M.). Each eye a nd calibration sphere were submitted to 10 serial examinations by usin g each system. The average K of all points within the central 3.0 mm o f the topography systems (central 3.0 mm) was compared with the averag e K of the manual keratometer. Results. All videokeratoscopy systems c orrelated well with each other and manual keratometry when accessing a spheric and spherocylinder calibration balls. EyeSys central keratomet ry clinical results had the strongest correlation with the average ker atometry results at 35%, followed by PAR-CTS at 25% and C-Scan at 5%. Among the videokeratoscopy units, EyeSys and PAR-CTS had the strongest correlation at 65%. The correlation between the TechnoMed C-Scan and both the EyeSys and PAR-CTS systems was 25%. There was a statistically significant difference (p < 0.05) between the systems when analyzing the results obtained from clinical subjects. The average keratometry ( K) difference of human eyes between videokeratoscopy systems is <0.35 diopters (D) (p < 0.05), which may be clinically significant. The aver age manual K reading (42.97 D) is statistically significantly flatter (p < 0.05) than each of the videokeratoscopy units (EyeSys = 43.49 D; PAR = 43.48 D; C-Scan = 43.83 D). Comparing the 10 measurements of eac h eye or calibration object in the same videokeratoscopy system verifi ed that the devices give reproducible results. The average standard de viation (ASD) of the keratometer was 0.10 D. The ASD of the videokerat oscopy units was 0.05 D for the EyeSys, 0.29 D for the PAR-CTS, and 0. 31 D for the C-Scan systems. Conclusion, Based on this study, we shoul d not assume that the results of different topography systems can be i nterchanged in clinical studies.