Comparison of Keratometry Measurements by High-Resolution Scheimpflug Imaging and Conventional Topography in Normal and Keratoconus Eyes
Narrative Responses:
Purpose
To evaluate the difference between the keratometry (K) obtained with the Pentacam high resolution (HR), and corneal topography in both normal and keratoconus.
Methods
60 eyes of healthy subjects and 35 eyes with keratoconus, diagnosed either clinically or by corneal topography, were examined prospectively. Keratometry measurements in the flat (Kf) and steep (Ks) meridians were taken with the ALLEGRO Topolyzer VARIO System (Alcon Surgical) followed by the Pentacam HR(Oculus, Wetzlar,Germany). The Test-retest variability (TVR), coefficient of variation (CoV) were calculated to evaluate the difference between the two instruments.
Results
By topography the mean Kf was 43.33 in normal & 45.41 in keratoconus.By pentacam the mean kf was 42.86 in normal& 45.28 in keratoconus.There was statistically significant difference between the two instruments in normal group only(p<0.001).The mean ks by topography was 44.62 in normal& 48.01 in keratoconus.By pentacam was 44.37 in normal& 48.87 in keratoconus.There was a statistically significant difference between the two instruments in both groups(p<0.001).In normal the CoV for kf and ks were(0.65, 0.48%),while in keratoconus the CoV was higher (0.80, 1.13%).In normal corneas the TVR for kf and ks were(0.68, 0.46).in keratoconus,TVR was higher for both(1.05, 1.51).
Conclusion
Pentacam HR keratometry measurement is higher than those obtained by corneal topography in both normal and keratoconus. This difference should be considered if we are using the pentacam data for procedures like IOL power calculation. Also for patient follow-up, one keratometry device is recommended