Comparison of Corneal Astigmatism Prediction Accuracy of Point-Source Color LED and Combined Placido–Dual Scheimpflug Corneal Topographers
Purpose
To evaluate the accuracy of corneal astigmatism prediction with a point-source color LED corneal topographer (Cassini, iOptics) and a combined Placido/Dual Scheimpflug corneal topographer (Galilei, Ziemer).
Methods
Both devices calculate total corneal power and astigmatism by combining anterior and posterior surface measurements. Corneal curvature and astigmatism will be measured in eyes undergoing cataract surgery with 1 diopter or more corneal astigmatism based on Lenstar automated keratometry. Measurements with the Cassini, Galilei, Atlas, and Lenstar will be performed before and 3 weeks after surgery. In eyes that receive a toric IOL, alignment of the toric lens will be recorded at both time points. The actual corneal astigmatism will be back calculated from the Holladay 1 formula using the post-operative refractive astigmatism and IOL orientation at the 3-week postoperative visit. The prediction error will be calculated as the difference between the astigmatism measured by each device and the actual corneal astigmatism. Vector analysis will be used in all calculations.
Results
Eyes will be divided into with-the-rule and against-the-rule astigmatism groups. Mean vector prediction errors and standard deviations for each device will be presented.
Conclusion
Both the Cassini and Galilei display total corneal astigmatism, which takes into account posterior corneal curvature and may have a theoretical advantage over Placido disc-based corneal topography. The performance of these devices in total corneal astigmatism prediction will be discussed.