Repeatability of Corneal Astigmatism Measurements
Narrative Responses:
Purpose
To compare the performance of three different corneal topographers and 1 tomographer in measuring corneal astigmatism.
Methods
This is an observational study of corneal astigmatism measurements from 60 eyes of 51 pre-cataract surgery patients (ages 55 to 75). Keratron (Optikon, Rome, Italy; Placido ring topography), Pentacam (Oculus, Wetzlar, Germany; rotating Scheimpflug tomography), Cassini (i-Optics, The Hague, The Netherlands; color LED reflection topography), and Lenstar LS 900 (Haag-Streit, Koeniz, Switzerland; monochromatic LED reflection topography) were used for the measurements. Corneal astigmatism was derived from the keratometric parameters Kflat and Ksteep and the corresponding axis of the flattest meridian was recorded. The SD of three trials was used to describe repeatability.
Results
Repeatability was 0.14 ± 0.14 diopters (D) @ 9.4 ± 5.8 deg for Keratron, 0.23 ± 0.15 D @ 14.9 ± 13.2 deg for Pentacam, 0.15 ± 0.13 D @ 4.8 ± 4.8 deg for Cassini, and 0.14 ± 0.12 D @ 6.5 ± 7.5 deg Lenstar. For astigmatism of > 0.5 D (n=43), repeatability was 0.15 ± 0.08 D @ 7.3 ± 4.1 deg for Keratron, 0.24 ± 0.17 D @ 12.2 ± 14.4 deg for Pentacam, 0.13 ± 0.12 D @ 4.1 ± 5.3 deg for Cassini, and 0.16 ± 0.12 D @ 6.0 ± 6.7 deg for Lenstar.
Conclusion
Repeatability of the various devices was similar for magnitude of astigmatism. For axis of astigmatism, repeatability was highest for color LED reflection topography. This was true for lower as well as for higher amounts of astigmatism.