Purpose: To examine the technique of second-pass femtosecond laser to correct an incomplete flap during laser in situ keratomileusis.
Setting: Department of Ophthalmology, Bascom Palmer Eye Institute, Miami, Florida, USA.
Methods: Twenty porcine eyes were assigned to 1 of 4 groups. In the first 2 groups, a flap was created with a femtosecond laser with a centrally black-painted applanator at a 200 microm depth; a second flap was created at a 400 microm depth with the normal applanator. These groups differed by waiting or not waiting for the opaque bubble layer (OBL) to clear. In the third and fourth groups, the eyes were separated into those with and without OBL; however, the same depth was used for the second pass, which was performed after intentional suction loss. After these treatments, the corneas were examined using anterior segment optical coherence tomography (AS-OCT) and the surgical microscope.
Results: In the first group (did not wait for OBL to clear), the peripheral shallow cut and the central deep line were observed in the AS-OCT images, with corresponding findings under the surgical microscope. In the second group (waited for OBL to disappear), there were 2 parallel lines on the AS-OCT images; the lines corresponded to dual flaps. In the third and fourth same-depth-cut tests, lines and irregularities were seen on the bed and the back of the flap.
Conclusion: A second femtosecond laser pass for incomplete flaps, especially when the OBL has cleared, may result in an uneven lamellar cut.