From all Lasik flap complication, LASIK flap buttonholes are those that lead most frequently to lack of best-corrected visible acuity (BCVA). Why do they occur? Skinny, irregular and perforated flaps appear to end result from a typical etiology; an insufficient coupling of the blade to the cornea. Steep corneas have been in comparison with tennis balls that may buckle centrally upon applanating pressure. This ends in a central dimple missed by the blade resulting in a buttonhole. One other idea is that increased keratometric values provide elevated resistance to chopping when applanated, resulting in upwards motion of the blade 임신중절수술.
The latter might be extra relevant to keratomes with decrease oscillation charges. Equally, flat corneas might end in a skinny and/or small flap as they may very well be under the enough chopping stage in sure areas. Insufficient blade to cornea coupling is usually because of poor suction (sunken globe/small diameter corneas with insufficient suction ring placement, conjunctival incarceration within the suction port…). Non-angled blades have equal probabilities of moving upwards in the direction of the floor or downwards in the direction of the stromal aspect if confronted with resistance. On the opposite hand, inferiorly angled blades usually tend to be pushed in the direction of the stroma. If a buttonhole is encountered (particularly centrally), most surgeons want to abort the process, substitute the flap and re lower a deeper flap (20-60 ?m deeper) roughly 10-12 weeks later. Whereas some advocate continuing with scraping the epithelium and performing a PRK laser ablation, we consider this method will not be possible in increased myopes as a result of look of surprising haze.
The next index for epithelial ingrowth ought to maintained across the margins of the buttonhole. The incidence of perforated flaps (in addition to skinny and irregular ones) could also be diminished if the surgeon ensures enough suction, inspects the blades and adjusts the keratome plate thickness in accordance with corneal curvature. Different useful measures embody making certain enough intraocular pressure earlier than chopping the flap. Measurement could also be most dear with a pneumotonometer as different means have been reported to offer imprecise readings at occasions. Care ought to be taken to keep away from conjunctival clogging within the suction port, which might result in discrepancy between the intraocular pressure and the suction pressure recorded on the microkeratome vacuum console. Newer microkeratomes have a safety mechanism to mechanically abort the process or to activate extra suction however are additionally liable to related issues if IOP measurements usually are not obtained to make sure enough suction. Some surgeons examine the microkeratome blade underneath the working microscope earlier than partaking it within the suction ring as a way to rule out manufacturing or different preoperative harm to the blade. It’s best to maintain the microkeratome away from arduous surfaces after meeting to keep away from subsequent blade harm.