The Three-Pass-Underpass Technique: A Graded Flap Dissection Technique for Thin Femtosecond Sub-Bowman Keratomileusis Flaps

Abstract

Femtosecond laser-assisted sub-Bowman keratomileusis has an occasional intraoperative complication of a flap tear. We describe a new technique (three-pass-underpass technique) to dissect and lift the flap to reduce the probability of a tear. This comparative case series, 150 consecutive cases of femtosecond-assisted flap creation for laser in situ keratomileusis underwent flap separation with the new (three-pass-underpass) technique. These cases were retrospectively compared with 150 consecutive cases performed with the conventional, single stroke technique. The three-pass-underpass technique is as follows: After docking, centration, and initiation of the femtosecond laser pass, the side cut was opened with the sharp end of the Siebel Spatula. The blunt end was then inserted from temporal side to make the first pass of the spatula, constituting little less than one third of the area to be separated. The second pass of the spatula covered entire pupillary area, and the remaining third was covered by a third pass. The spatula was then inserted under the flap in the centre, and the flap was then freed up to the hinge by a sweeping movement toward the temporal and nasal periphery. Comparable visual-refractive outcomes and lesser flap tear rate were noted with the new technique compared with the conventional technique. The three-pass-underpass technique seems to be a safe alternative to the conventional single-stroke technique for dissecting sub-Bowman flaps.