Abstract:

Objective    To evaluate the correlation between diameter of corneal flap created by LDV femtosecond laser and corneal curvature (K), so as to provide clinical evidence for the choice of suction ring to satisfy patients with different corneal curvature. Methods    Fifty myopic patients (100 eyes) who had femtosecond-assisted LASIK surgery from February to April 2013 in Peking Union Medical College Hospital were included in this study. Patients were divided into two groups based on the diameter of suction ring used in the creation of corneal flap. Thirteen patients (26 eyes) who used suction ring of 9.0mm were in Group Ⅰ, while the other thirty-seven patients (74 eyes) who used suction ring of 8.5mm were in Group Ⅱ. All the procedures were done by the same skillful surgeon who also measured the diameter of the cornea and the flap, and the corneal curvature during each procedure. An independent samples t test and bivariate correlation method were used to analyze the quantitative data. Results    There were eighteen males (36 eyes) and thirtytwo females (64 eyes) in this study aged 18 to 37 (average 24.6) years old. Patients all underwent binocular surgery and no intra-operative complication occurred. The average diameter of the cornea in each group was 10.7mm and 10.6mm respectively (t=0.04, P<0.05). The average diameter of the corneal flap in Group Ⅰ was 9.2mm, and for patients whose corneal curvature was greater than 44.0D, between 42.0D and 44.0D, or less than 42.0D, their average corneal flap diameter was 9.3mm, 9.1mm, and 8.6mm respectively, which showed a significant positive correlation between the corneal curvature and the corneal flap diameter (r=0.492, P=0.027). The average diameter of the corneal flap in Group Ⅰ was 8.3mm, and for patients whose corneal curvature was greater than 44.0D, between 42.0D and 44.0D, or less than 42.0D, their average corneal flap diameter was 8.4mm, 8.3mm, and 8.0mm respectively, which also showed a significant positive correlation between the corneal curvature and corneal flap diameter (r=0.513, P=0.001). Conclusion    The diameter of corneal flap created by LDV femtosecond laser is strongly correlated with corneal curvature, meaning patients with a high K Value tended to have a bigger corneal flap than patients with a relatively low K Value in femtosecond-assisted LASIK surgery. It suggest that surgeons should choose suction rings that are relatively bigger for patients with a low K Value in order to prevent creation of small or even free corneal flaps. And for patients with a high K Value, suction rings that are relatively smaller are recommended, in order to prevent creation of large corneal flaps, intraoperative bleeding, and post-LASIK dry eye.

Key words: Corneal flap, Corneal curvature,  LDV femtosecond laser, Correlation