Background: The hinge technique greatly improves the results of automated lamellar keratoplasty but makes it impossible to measure the thickness of the corneal cap with a micrometer. We developed a technique of measuring cap and stromal disc thickness with a pachometer and compared the results with those obtained with a micrometer.
Methods: Measurements of the thickness of the stromal disc and/or corneal cap were taken with the Mitutoyo micrometer and the Chiron Corneo-Gage System III pachometer in five myopic and three hyperopic cases undergoing automated lamellar keratoplasty with complete cap resection. The intended postoperative refraction was plano. Postoperative refractions were taken at two months.
Results: In most cases, the corneal cap measured thinner while the stromal disc measured thicker by the micrometer than by the pachometer because of the hydration status of the stromal bed. In both myopic and hyperopic cases, the thickness measurements taken with the pachometer correlated better with the postoperative spherical equivalent values than those taken with the micrometer.
Conclusions: The thickness measurement of corneal resections by both micrometry and pachometry is greatly influenced by tissue hydration status. When hydration is similar, the pachometer provides more accurate thickness readings than does the micrometer, as determined by correlations with intended refractive results.