The effect of hinge location on corneal sensation and dry eye after LASIK: a systematic review and meta-analysis

The aim of this meta-analysis is to investigate the possible effect of hinge location on corneal sensation and dry eye syndrome after laser-assisted in situ keratomileusis (LASIK). A comprehensive literature search was conducted in the PubMed, EMBASE, and Cochrane Controlled Trials Register to identify potentially relevant randomized controlled trials (RCTs) of comparing the effects of horizontal-hinge flaps and vertical-hinge flaps on corneal sensation and dry eye after LASIK. Meta-analyses were performed for corneal sensation, tear break-up time (TBUT), Schirmer's I test and corneal fluorescein staining (CFS) at 1 week, 1, 3, and 6 months postoperatively. Eight RCTs (657 eyes) investigating the effects of hinge location on the corneal sensation and dry eye syndrome after LASIK were identified. The results showed that the horizontal-hinge group causes less loss of sensation than the vertical-hinge group, and the difference was significant at 3-month postoperative (p = 0.01). The TBUT value was significantly larger and a lower percentage of patients with CFS in the horizontal-hinge group than in the vertical-hinge group at 1-month postoperative (p = 0.007 and p = 0.01, respectively) and 3-month (p = 0.03 and p = 0.009, respectively); Schirmer's I test values were also higher in the horizontal-hinge group, but the difference did not reach statistically significance at each postoperative period. According to the available data, we suggest that hinge location may have some effect on corneal sensation and dry eye syndrome after LASIK at the early postoperative period. However, there was no significant difference between the groups at 6 months after surgery. Further well-organized, prospective, randomized studies involving more patients are warranted.