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 consequence from a typical etiology; an insufficient coupling of the blade to the cornea. Steep corneas have been in comparison with tennis balls that will buckle centrally upon applanating pressure. This leads to a central dimple missed by the blade resulting in a buttonhole. One other concept is that larger keratometric values supply elevated resistance to slicing 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 could lead to a skinny and/or small flap as they might be under the satisfactory slicing degree in sure areas. Insufficient blade to cornea coupling is usually as a result of poor suction (sunken globe/small diameter corneas with insufficient suction ring placement, conjunctival incarceration within the suction port…). Non-angled blades have equal possibilities of moving upwards in direction of the floor or downwards in direction of the stromal aspect if confronted with resistance. On the opposite hand, inferiorly angled blades usually tend to be pushed in direction of the stroma. If a buttonhole is encountered (particularly centrally), most surgeons desire to abort the process, exchange 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 imagine this method is probably not possible in larger myopes as a result of look of surprising haze.
A better 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 lowered if the surgeon ensures satisfactory suction, inspects the blades and adjusts the keratome plate thickness in line with corneal curvature. Different useful measures embrace making certain satisfactory intraocular pressure earlier than slicing the flap. Measurement could also be most respected with a pneumotonometer as different means had been reported to offer imprecise readings at instances. Care must be taken to keep away from conjunctival clogging within the suction port, which may result in discrepancy between the intraocular pressure and the suction pressure recorded on the microkeratome vacuum console. Newer microkeratomes have a safety mechanism to robotically abort the process or to activate extra suction however are additionally susceptible to related issues if IOP measurements usually are not obtained to make sure satisfactory suction. Some surgeons examine the microkeratome blade below the working microscope earlier than participating it within the suction ring in an effort to rule out manufacturing or different preoperative injury to the blade. It’s best to maintain the microkeratome away from arduous surfaces after meeting to keep away from subsequent blade injury.