Measurement Of The Relative Accuracy Of The Corneal Analysis System Versus Keratometry And Auto Keratometry.

With the advent of new surgical techniques to correct refractive error, the need to accurately measure the anterior corneal surface in a reproducible fashion has led to a revolution of new instrumentation. The computerized video keratographer has been in some instances able to supplant more conventional means (keratometry, keratoscopy and photokeratography) of measuring the corneal curvature. Each instrument uses a different technique so there always arises the possibility that one instrument is not as accurate or reproducible as another. Several studies have been published to address this issue with special attention focused on the computerized topographer. This instrument uses mathematical equations called algorithms to interpret the distance between reflected placido rings to assess the corneal curvature at any point on the cornea. The Corneal Analysis System (EYESYS) has been determined to be very accurate when using calibrated spherical steel balls. Since the algorithm complexity increases for trying to interpret aspheric corneas, the chance for error also goes up. The purpose of the study is to assess the validity of these algorithms on the very irregular shape of a human cornea. Another factor to consider is the inability to determine the absolute accuracy of any instrument when measuring the human cornea. Since the absolute power of any given cornea is not known, one can only relatively
compare the accuracy of any given technique.