Diamond knife corneal incisions

In the following study, eight linear corneal incisions were made in two human cadaver eyes with three diamond-bladed knives: the KOI, Cooper, and Micra micrometer knives. Prior to the incisions, ultrasonic pachymetry readings of the corneas were recorded, and all knives were calibrated to a guarded cutting depth of 0.55 mm (550 microns). Following the incisions, the corneas were fixed, sectioned, and incision depth carefully measured histologically. In all but two incisions made with the Cooper knife, the incision depth was significantly or highly significantly greater than the calibrated diamond length. There was a significant or highly significant difference in depth among incisions made with the same knife, as well as among incisions made with different knives. Depth variability was noted for all knives except for two comparisons between incisions made with a Micra and KOI knife, and one comparison between two incisions, both made with the Cooper knife. Difference in knife design which may account for the variation of incision depth and contribute to the unpredictability of radial keratotomy is discussed.