Comparison Of Simulated K's As Measured By The B&L Keratometer To The EyeSys Corneal Analysis System And The Alcon Hand-Held Keratometer.

Reliance on the reproducibility of corneal measurements is very important to the success and satisfaction patients experience with their eye care providers. The procedures most reliant upon corneal measurements include the fitting of rigid gas permeable lenses and surgical alteration of the cornea to correct refractive errors. Several systems are available to assist in the measurement of corneal curvature. The standard is the keratometer, but as we have become more technologically advanced, sophisticated computerized videokeratographers (CVK's) have made their way onto the market and into the office of practicing optometrists and ophthalmologists. Companies who manufacture and market CVK's claim they provide more information, are more reliable and give more accurate measurements of toric surfaces than the standard keratometer. The commonly used manual keratometer observes the first Purkinje image reflected from the cornea and relates the size of the corneal reflections from a collimated source to the cornea's radius of curvature.1 It assumes a spherocylindrical shape and measures the image at two or four points around a circle that is 2.8 to 4.0 mm in diameter depending on the corneal power] -3 The portable hand held Alcon keratometer interprets corneal curvature by interpreting the distance between reflected images of a projected beam onto the cornea. The distance between images is converted into steepest and flattest images using vergence relationships. 4 The EyeSys system, as with most other CVK's, measures corneal curvature by reflecting a Placido disk onto the cornea. Distortions in the rings that are reflected from the corneal surface are analyzed using algorithms that are based on tested calibration spheres and maintained in look-up tables within the computer's memory 3-6 In this study we compare the measurements of three PMMA to toric lenses of known tori city and ten human corneal surfaces using the manual B&L keratometer, Alcon hand-held keratometer and the EyeSys II system. With this data we have attempted to see if there are any significant differences between measurements taken by the manual keratometer, which is our standard instrument for comparison, versus the Alcon and the EyeSys units.