A comparison of the ARK-700A autokeratometer and Medmont E300 corneal topographer when measuring peripheral corneal curvature.

PURPOSE

The purpose of this study was to evaluate if corneal topogometry measurements as taken with the ARK-700A autokeratometer are comparable with those measured by the Medmont E300 videokeratoscope at corresponding locations.

METHODS

Central and peripheral radius and eccentricity were measured in 122 right eyes of young normal subjects using autokeratometry and videokeratoscopy, obtained in a random order.

RESULTS

Curvature measurements obtained with the ARK700A and Medmont E300 correlated well for the central cornea. Larger differences were observed between peripheral autokeratometry readings and the empirically determined corresponding locations with the videokeratoscope. Correlations between the instruments are inconsistent, resulting in unacceptable confidence intervals. Corneal eccentricity was significantly different between the instruments for the vertical (t = 2.4; p = 0.018) and for the horizontal meridians. In the first case, the difference between the averaged values was not clinically significant, but in the horizontal meridian the AK significantly overestimated eccentricity values (t = -11.5; p < 0.001) with differences which were clinically significant.

CONCLUSIONS

Central corneal curvature data obtained by ARK700A and Medmont E300 can be interchanged but the same is not true of peripheral determinations of corneal shape. ARK700A probably measures peripheral corneal shape within an elliptical region between 5 and 7 mm in diameter, with the major axis in the vertical meridian.