Comparison of Holladay equivalent keratometry readings and anterior corneal surface keratometry measurements in keratoconus

Abstract

Purpose: To compare the accuracy of the anterior corneal simulated keratometry (SimK) and the Holladay equivalent keratometry reading (EKR) provided by a Scheimpflug camera (Pentacam HR) with the keratometry (K) provided by a Placido system (T-Cone topography) in keratoconus and control eyes.

Methods: This prospective study included 40 consecutive patients with keratoconus and 40 voluntary participants with no ocular complaints. Any patients with corneal scar, corneal trauma, history of corneal surgery or contact lens usage were excluded from the study. Mean SimK and Holladay EKR measurements were taken with Pentacam HR in the 2, 3, and 4.5 mm corneal zones, and these values were compared with the T-Cone mean K value with the Placido topography system attachment on the Lenstar LS 900. Statistical analysis was performed using the paired Student's t test and the Bland-Altman analysis.

Results: A statistically significant difference was determined between the Placido K and the Scheimpflug EKR 2, 3, 4.5 mm and SimK values in the keratoconus group (p < 0.05). In the analyses which showed a difference between the SimK and Holladay EKR, it was observed that as the diameter of the corneal zone increased, the 95% LoA values were extended. No statistically significant difference was determined between the SimK and EKR 2 mm values (p > 0.05). In the control group, there was no statistically significant difference between any of the keratometric values.

Conclusion: In diseases which affect the posterior corneal surface, such as keratoconus, it is thought that because of the asymmetrical peripheral placement of the corneal apex, as the corneal diameter increases there could be an error increase of 1-3 mm in keratometric systems evaluating the anterior surface.

Keywords: Equivalent keratometry reading; Keratoconus; Placido; Scheimpflug.