Corneal topography with an aberrometry-topography system.

PURPOSE: To investigate the agreement between the central corneal radii and corneal eccentricity measurements generated by the new Wave Analyzer 700 Medica (WAV) compared to the Keratograph 4 (KER) and to test the repeatability of the instruments.

METHODS: 20 subjects (10 male, mean age 29.1 years, range 21-50 years) were recruited from the students and staff of the Cologne School of Optometry. Central corneal radii for the flat (rc/fl ) and steep (rc/st ) meridian as well as corneal eccentricity for the nasal (enas ), temporal (etemp ), inferior (einf ) and superior (esup ) directions were measured using WAV and KER by one examiner in a randomized order.

RESULTS: Central radii of the flat (rc/fl ) and steep (rc/st ) meridian measured with both instruments were statically significantly correlated (r = 0.945 and r = 0.951; p < 0.001). Comparison between the WAV and KER showed that rc/fl and rc/st measured with WAV were significantly steeper than those measured with KER (p < 0.001). Corneal eccentricities were statistically significantly correlated in all meridians (p < 0.05). Compared to KER, etemp and esup measured with WAV were greater (p < 0.05), while there were no statistically significant differences for enas and einf (p = 0.350 and p = 0.083). For the central radii, repeated measurements were not significantly different for the KER or WAV (p > 0.05). Limits of agreement (LoA) indicate a better repeatability for the KER compared to WAV.

CONCLUSIONS: Corneal topography measurements captured with the WAV were strongly correlated with the KER. However, due to the differences in measured corneal radii and eccentricities, the devices cannot be used interchangeably. For corneal topography the KER demonstrated better repeatability.