A corneal flap is a thin, superficial layer of corneal tissue, typically 90-160 micrometres thick, consisting of epithelium, Bowman's membrane and superficial layers of dermis, which is created and deflected during LASIK (Laser-Assisted In Situ Keratomileusis) surgery to access the deeper layers of the corneal stroma. The flap can be created mechanically using a microkeratome (oscillating surgical blade) or by a bladeless method using a femtosecond laser (femto-LASIK), with the femtosecond laser providing greater precision in flap thickness and geometry and better repeatability of the procedure. The flap remains connected to the cornea by a 3-5 mm wide hinge (hinge), usually located in the upper or nasal part of the cornea, which allows the flap to be deflected, laser ablation of the stroma performed and then repositioned.
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