A Prospective Randomized Comparison of Four Femtosecond LASIK Flap Thicknesses

Abstract

To evaluate the visual outcomes, predictability, and planarity of four types of 60-kHz femtosecond laser-assisted LASIK flaps: 90, 100, 110, and 120 microm. This randomized, prospective, interventional, comparative trial was performed at a tertiary care facility. Two hundred forty eyes with a calculated residual bed thickness >300 microm (at 120-microm flap thickness and subjective refraction) were randomized into four flap thickness groups to undergo femtosecond laser-assisted LASIK. Pre- and postoperative assessment included uncorrected visual acuity, best spectacle-corrected visual acuity (BSCVA), and refraction. Flap thickness was assessed by anterior segment optical coherence tomography on 28 points per flap at 1-month follow-up. Three new indices were devised to assess the predictability and planarity. The baseline parameters were matched. Postoperative vision and refractive outcome were similar in the four groups (P>.05, analysis of variance). The achieved flap thickness was different at each measured point among the groups (P<.05) with standard deviations ranging from +/-3.2 to +/-7.3 microm. The predictability and planarity were satisfactory in all four groups, although the indices were slightly better in the 110-microm and 120-microm groups. No loss of BSCVA or flap complications occurred in the four groups. The study demonstrated that all four flap thicknesses are relatively uniform in predictability and clinical outcomes.