Effect of resection velocity and suction ring on corneal flap formation in laser in situ keratomileusis

Purpose: To determine the effects of microkeratome-cutting velocities and the suction ring on corneal flap creation. Setting: Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, Korea. Methods: Procedures were performed under clinical settings in 65 pig eyes. Keratometric diopters (D) were measured before and after application of the suction ring. Corneal thickness was measured before and after resection cutting; and the difference was taken as flap thickness. The microkeratome was initially set at a resection thickness-of 160 mu m. The blade oscillation (turbine velocity) was set at 30, 35, and 42 psi. The translational velocity was arbitrarily divided into high (1 to 2 seconds), moderate (3 to 5 seconds), and low (6 seconds or more). Data were analyzed by varying the velocities consecutively. Photographs of the cut surface were acquired by scanning electron microscopy to evaluate resection morphology by comparison. Results: Mean refractive powers were 39.94 D +/- 0.66 (SD) and 39.69 +/- 0.98 D before and after application of the suction ring, respectively; however, no significant difference was observed (P = .216). Lower surgeon translational velocity resulted in a significantly thicker corneal flap in 8 of the 9 paired comparisons (P < .05). Higher turbine velocity resulted in a significantly thicker corneal flap in 7 of the 9 paired comparisons (P < .05). The cut surface was smoother at higher turbine and lower translational velocity. The initial cut margin was steeper at higher translational velocity. Conclusions: The increase in intraocular pressure induced by the suction ring had no significant effect on keratometric power. At higher turbine and lower translational velocities, the corneal flap was thicker and the cut surface smoother, Higher translational velocities made the initial cut margin steeper. J Cataract Refract Surg 1999;25:1448-1455 (C) 1999 ASCRS and ESCRS.