CLINICAL-EVALUATION OF KERATOMETRY AND COMPUTERIZED VIDEOKERATOGRAPHY- INTRAOBSERVER AND INTEROBSERVER VARIABILITY ON NORMAL AND ASTIGMATIC CORNEAS

Aims-To evaluate intra-and interobserver variability in measurements o n normal and astigmatic corneas with keratometry and computerised vide okeratography. Methods-Keratometric readings with the 10 SL/O Zeiss ke ratometer and topographic maps with the TMS-1 were obtained by two ind ependent examiners on 32 normal and 33 postkeratoplasty corneas. Inter -and intraobserver coefficients of variability (COR) for measurements of steep and flat meridian power and location, in addition to the magn itude of astigmatism, were assessed. Results-Compared with TMS-1, the 10 SL/O keratometer showed a superior repeatability in measuring norma l corneas (intraobserver COR for keratometry and TMS-1 respectively: 0 .22 and 0.30 D for steep meridian power; 0.18 and 0.44 D for flat meri dian power; 0.26 and 0.40 D for astigmatism; 5 degrees and 26 degrees for steep meridian location; 5 degrees and 13 degrees for hat meridian location). Astigmatism intraobserver COR (0.20 D and 0.26 D for the t wo observers) and interobserver COR (0.28 D) of the keratometer for no rmal corneas was very good and not affected by observers' experience. Repeatability of the TMS-1 on normal corneas was found to be: (a) obse rver related, and Cb) astigmatism related. A novice observer showed a much greater COR (1.62 D for astigmatism, 30 degrees for flat meridian location) compared with the experienced examiner (0.40 D for astigmat ism, 13 degrees for flat meridian location). Higher deviation scores w ere observed for corneas with higher astigmatism. For the postkeratopl asty corneas, again the keratometer achieved superior reproducibility (astigmatism interobserver COR 1.12 D for keratometry, 4.06 D for TMS- 1; steep meridian location interobserver COR 10 degrees for keratometr y, 34 degrees for TMS-1).Conclusion-Keratometric readings are more rep roducible than topographic data both for normal and postkeratoplasty c orneas. The two instruments should not be used interchangeably especia lly on highly astigmatic corneas. For the TMS-1, users with the same l evel of experience should be employed in clinical or experimental stud ies.