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. 1998 Jun;82(6):637–642. doi: 10.1136/bjo.82.6.637

Clinical evaluation of keratometry and computerised videokeratography: intraobserver and interobserver variability on normal and astigmatic corneas

C Karabatsas 1, S Cook 1, J Papaefthymiou 1, P Turner 1, J Sparrow 1
PMCID: PMC1722645  PMID: 9797664

Abstract

AIMS—To evaluate intra- and interobserver variability in measurements on normal and astigmatic corneas with keratometry and computerised videokeratography.
METHODS—Keratometric readings with the 10 SL/O Zeiss keratometer and topographic maps with the TMS-1 were obtained by two independent 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 magnitude of astigmatism, were assessed.
RESULTS—Compared with TMS-1, the 10 SL/O keratometer showed a superior repeatability in measuring normal 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 meridian power; 0.26 and 0.40 D for astigmatism; 5° and 26° for steep meridian location; 5° and 13° for flat meridian location). Astigmatism intraobserver COR (0.20 D and 0.26 D for the two observers) and interobserver COR (0.28 D) of the keratometer for normal corneas was very good and not affected by observers' experience. Repeatability of the TMS-1 on normal corneas was found to be: (a) observer related, and (b) astigmatism related. A novice observer showed a much greater COR (1.62 D for astigmatism, 30° for flat meridian location) compared with the experienced examiner (0.40 D for astigmatism, 13° for flat meridian location). Higher deviation scores were observed for corneas with higher astigmatism. For the postkeratoplasty 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° for keratometry, 34° for TMS-1).
CONCLUSION—Keratometric readings are more reproducible than topographic data both for normal and postkeratoplasty corneas. The two instruments should not be used interchangeably especially on highly astigmatic corneas. For the TMS-1, users with the same level of experience should be employed in clinical or experimental studies.

 Keywords: keratometry; computerised videokeratography; astigmatic corneas

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Figure 1  .

Figure 1  

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Variability of astigmatism measurement (D) with the TMS-1 on normal corneas (A) for observer 1; (B) for observer 2. 

Figure 2  .

Figure 2  

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Variability of keratometric readings on post-PKP corneas (A) observer 1; (B) observer 3; (C) interobserver variability for observers 1 and 3. 

Figure 3  .

Figure 3  

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Variability of topographic measurements with the TMS-1 on post-PKP corneas. (A) Observer 1; (B) observer 3; (C) interobserver variability for observers 1 and 3. 

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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