Reproducibility study of Placido-based corneal topography systems

Background: We have developed a computer software program that analyzes the reproducibility of corneal topography systems. Methods: Using a Macintosh computer with Microsoft QuickBasic programming we created a program that records and analyzes the corneal power of 72,000 points per topography map (200 points over each one degree meridian) by linear interpolation of the Placido-based ring data. Reproducibility studies on 7 normal and 7 abnormal (pathological and postsurgical) corneas were performed with 2 Placido ring based topography systems the EyeSys Corneal Analysis System (CAS) and the Humphrey MasterView system. Five exams were performed by two technicians each. The mean, range and standard deviation of corneal power was calculated for all points on a map, and represented pictorially for each patient. Statistical analysis of standard deviation at each point was used in assessing the reproducibility between systems and between technicians. Results: The topographic maps of mean power range and standard deviation are presented for selected patients. The overall mean standard deviation of power and the means within concentric annular zones and quadrants are presented for each system and technician for both normal and abnormal cornea. Intraobserver variability of each system were not significantly different for both normal and abnormal corneas. There was no significant difference between technicians, nor were there regional differences in variability.standard deviation of power is presented for each system and technician comparing intersystem and intraobserver variability for both normal and abnormal corneas. Conclusion: A precise method of analyzing multiple variables of reproducibility in corneal topography is now available through a new proprietary software system.