Effects of flap diameter on dry eye parameters and corneal sensation after femtosecond laser-assisted LASIK

PURPOSE: Although femtosecond laser-assisted LASIK (laser-assisted in situ keratomileusis). provides a controllable flap size than a mechanical microkeratome, patients still experience dry eye symptoms after LASIK.The purpose of this study is to investigate the effects of different flap sizes on postoperative dry eye syndrome and corneal sensitivity. PATIENTS AND METHODS: This is a retrospective comparative study. Fifty-seven consecutive patients (113 eyes) who underwent myopic femtosecond laser-assisted LASIK treatment were recruited. Basic Schirmer's test value, tear breakup time (TBUT), corneal fluorescein staining scores, conjunctival rose bengal staining scores, and corneal sensitivity were measured before surgery, at postoperative 1, 3, and 6 months follow-up. RESULTS: When the eyes were grouped by flap diameter sizes (8.7 mm as the cutoff value), there were no significant differences in terms of corneal sensitivity and all dry eye parameters investigated at any time points between the large or small flap diameter groups. However, when the eyes were grouped by the ratio of flap diameter/horizontal corneal white-to-white distance (0.756 as the cutoff value), the larger ratio group showed decreased basic Schirmer's test (7.52 ± 4.43 mm) than the smaller group (12.15 ± 8.14) at 3 months (P = 0.006). Moreover, the group that had larger flap/corneal diameter ratio showed shorter TBUT (4.20 ± 1.73 s) than the smaller group (5.67 ± 1.90 s) at 6 months postoperatively (P = 0.011). CONCLUSIONS: LASIK-related dry eye syndrome was associated with flap/corneal diameter ratio, and surgeons should keep this effect in mind when customizing the cornea flap sizes for dry eye patients during LASIK.