LASIK flap hinge position demonstrates no effect on corneal sensation, dry eye

This prospective study evaluated the effect of superior- versus nasal-hinged flaps on corneal sensation and dry eye after femtosecond laser-assisted LASIK for myopia and found that hinge position had no significant effect on corneal sensation or dry eye parameters. The authors suggest that selection of hinge position can be made according to the surgeon's preference. They say that for patients with high myopia and preoperative symptoms of dry eye, more aggressive postoperative dry eye regimens may be needed.

This is the first study to compare nasal vs. superior hinge location. Forty-three patients underwent bilateral femtosecond laser-assisted LASIK for moderate to high myopia (up to -15.00 D) with a superior hinge flap created in the right eye and a nasal hinge in the left eye. All patients had signs of dry eye prior to surgery. For this reason, they all received punctual plugs immediately after surgery.

The investigators evaluated corneal sensation, tear break-up time, ocular surface staining, and subjective dry eye symptoms for six months postoperatively. They found no differences between the nasal hinge and superior hinge groups one, three or six months after surgery in any of these parameters.

Corneal sensation was significantly decreased after surgery in both groups and required three months to return to baseline. Tear break-up time and Rose Bengal staining of the conjunctiva showed no significant change in either group from baseline. Schirmer test scores showed increased basal tear secretion in both groups starting one month after surgery, although this is affected by punctual occlusion. Fluorescein staining of the cornea increased in both groups but returned to baseline gradually. The ocular surface disease index increased in both groups and remained greater than preoperative scores, even at the six-month visit.

Previous studies examining the effect of flap hinge location (nasal vs. superior) on corneal sensation and dry eye syndrome after microkeratome assisted LASIK have reported conflicting results. Researchers have speculated that major corneal nerve fibers at 9:00 and 3:00 could be spared by varying hinge position, although this anatomical model has been replaced by studies showing equal distribution of corneal nerve trunks.

The authors of the current study conclude that femtosecond laser-assisted LASIK reduced corneal sensitivity and led to increased corneal staining postoperatively, although these parameters returned to baseline values within six months. They recommend considering postoperative punctal plug occlusions for patients who present with dry eye symptoms before LASIK.