PURPOSE:

To analyze the clinical features and the risk factors leading to formation of flap buttonhole during laser in situ keratomileusis (LASIK) and the postablation visual outcome.

Medical records of all eyes that developed flap buttonhole during LASIK were retrospectively reviewed. Pre-LASIK measurements and intraoperative parameters were analyzed to predict the risk factors.

A total of 944 eyes underwent LASIK during the study duration. Four eyes (0.42%) developed partial thickness flap buttonhole. Thin-flap LASIK (flap thickness < or =90 microm) was performed in 230 eyes. The incidence of buttonholes in thin-flap LASIK cases was 1.7% (4 of 230). LASIK procedures were performed at a tertiary eye institute between October 2006 and December 2008. The mean age was 31 +/- 8.7 years. Preablation mean spherical refractive error in the affected left eye was -7.8 +/- 1.2 diopters (D), mean steeper axis keratometry was 44.0 +/- 1.56 D, and the mean pachymetry was 520 +/- 16 microm. Buttonholing in the flap occurred in the second (left) eye of all 4 cases. All cases had undergone thin-flap LASIK with 90-microm blade using the Moria M2 microkeratome. Flap diameter was +2/7.5 and 0/8.0 for 2 eyes each. Twelve weeks after the initial procedure, transepithelial phototherapeutic keratectomy/photorefractive keratectomy was performed in all 4 eyes. Postablation visual outcome was 20/20 and 20/25 in 2 eyes each. One patient had a faint subepithelial scar at the last 1-year follow-up.

Formation of flap buttonhole is significantly more common in the second eye and with the usage of Moria M2 microkeratome and 90-microm blade. In thin-flap LASIK, the practice of using the same microkeratome blade for the fellow eye, as is commonly followed at many refractive surgery centres, should be abandoned. Intraoperative subtraction pachymetry may be helpful in predicting the risk of buttonhole in the second eye. These precautions are especially mandatory in thin-flap LASIK irrespective of the other associated risk factors.