Flap Thickness and the Risk of Complications in Mechanical Microkeratome and Femtosecond Laser In Situ Keratomileusis: A Literature Review and Statistical Analysis

Abstract

Introduction: A recent Cochrane review found no difference in visual acuity outcomes between femtosecond-assisted laser in situ keratomileusis (LASIK) and LASIK using mechanical microkeratomes (MMKs). This study compares the flap thickness and risk of complications related to flap creation using femtosecond lasers and MMKs. Methods: PubMed and the Web of Science are used to search the medical literature. An extensive search is performed to identify the flap thickness and complications of LASIK as reported up to Jul 15, 2021. The following keywords are used in various combinations: Corneal flap, femtosecond laser, laser in situ keratomileusis, laser-assisted in situ keratomileusis, LASIK, mechanical microkeratome. Results: After removing duplicates and irrelevant studies, 122 articles were included for review. Pooled differences for intended vs. postoperative flap thickness using MMKs and femtosecond laser were −4.07 μm (95% CI: −19.55, 3.24 μm) in studies on the MMK and 5.43 μm (95% CI: 2.30, 7.84 μm; p < 0.001), respectively. After removing the studies evaluating outcomes of the old generation Hansatome MMKs (which had a significantly greater variation of flap thickness), the pooled difference for newer MMKs was 4.97 μm (95% CI: 0.35, 9.58 μm; p < 0.001), but the results still favored the femtosecond laser. Uncommon and mild complications unique for the femtosecond LASIK are epithelial gas breakthrough, opaque bubble layer, transient light sensitivity syndrome, and rainbow glare. A single study reported a very low, but stastically different risk of postoperative flap slippage (0.033% for MMK LASIK, and 0.003% for femtosecond LASIK, respectively). Conclusion: In both manual microkeratome and femtosecond LASIK, intra- and postoperative complications were uncommon. The evidence of the superiority of one technique in terms of complications over another cannot be indisputably stated.

Early LASIK flap displacement without signs of infection

“…It is more difficult to achieve an even thickness flap using mechanical keratome vs femtosecond laser. 3 Increased thickness of the flap leads to greater rotational forces, which tends to produce folds at the nasal hinge, as seen in this patient. 4 In addition, uneven thickness can cause microdisplacements.…”

Efficiency of Moria One-Use Plus Sub-Bowman’s Keratomileusis Head in Achieving Predicted Corneal Flap Thickness in Sub Bowmans Keratomileusis

“…Contrary to that Kanclerz P et al have shown that the evidence of the superiority of one technique in terms of complications over another cannot be stated. 20 In our study the resultant corneal flap thickness was found as 101.18 ± 3.51 in right eye (p < 0.05) and 100.61 ± 3.49 in left eye (p > 0.05) which was statistically significant in right but insignificant in left eye respectively from the predicted value. There is a highly significant mean difference in resultant corneal flap thickness (P < 0.0001) of right and left eye.…”

Corneal foreign body post laser in-situ keratomileusis: Diagnosis, management, outcome and review of literature

“…Flap looked like a meniscus flap suggestive of microkeratome LASIK. 6 CFB caused a buttonhole in the flap with the flap margin delineated inferiorly ( Fig. 2 b).…”

“… 2 Post-LASIK patients have a risk of suffering additional flap related complications when sustaining trauma or foreign body (FB) fall. 3 Occurrence and management of trauma related flap complications like flap tear, avulsion, diffuse lamellar keratitis (DLK), 4 , 5 , 6 etc have been well reported in literature but there are very few reports describing the incidence of penetrating trauma or corneal foreign bodies (CFB) and their management. Post-LASIK eyes in addition to routine foreign body work up require careful inspection of flap and stromal bed.…”