INTRAOCULAR-TENSION INCREASE IN MICROKERA TOME SECTIONS (LASIK) AND IN KERATOPLASTY WITH THE GTS TREPHINE SYSTEM

Microkeratome systems are being increasingly applied in lamellar corne al surgery (e. g., LASIK). The results of the few studies on intraocul ar pressure changes during the microkeratome cut vary widely. In this study, we examined the intraocular pressure pattern (IOP) in relation to the initial pressure. Methods: We performed lamellar corneal cuts o n freshly enucleated porcine bulbs with three different microkeratome systems and different setting for the initial pressure (10, 20 and 30 mm Hg). The bulbs were cannulated, and the IOPs were recorded online w ith a two-chamber measuring system. In addition, we examined the GTS t rephine system applied for corneal transplantation. Results: It became obvious that there were significant differences between systems (sign ificance level, P = 0.05). With an initial pressure of 10 mm Hg the me asured values of the Schwind system are significantly lower than with the Polytech system, and these values are again significantly lower th an with the Chiron microkeratome. With 20 mm Hg the Chiron system show s significantly higher values than both other systems. With 30 mm Hg i nitial pressure, the pressure values with the Schwind system and with the Chiron microkeratome are significantly higher than with the Polyte ch system. Thus with all microkeratome systems the middle and maximum pressure values rise in correlation with the initial pressure levels. This effect was not seen with the trephine system. With the same initi al pressure, the standard deviation of the measured data of different mikrokeratomes was low (range 3.1-9.0 mm Hg). Conclusion: The pressure values shown are higher than the data published by the manufacturers. There is current discussion are to whether these pressure values are dangerous (e. g. bleeding) or not. The pressure values reached intraoc ularly during the microkeratome cut depend on the system and also on t he present initial intraocular pressure values. Only with the same ini tial pressure can reproducible applanation and cutting conditions be o btained, which guarantee stable quality of the cut.