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Managing Lasik Flap Buttonholes
By: Sam Melki
From all Lasik
flap complication, LASIK
flap buttonholes are the ones that lead most often to loss of
best-corrected visual acuity (BCVA). Why do they happen?
Thin, irregular and perforated flaps seem to result from a common
etiology; an inadequate coupling of the blade to the cornea. Steep
corneas have been compared to tennis balls that would buckle centrally
upon applanating pressure. This results in a central dimple missed by
the blade leading to a buttonhole. Another theory is that higher
keratometric values offer increased resistance to cutting when
applanated, leading to upwards movement of the blade. The latter is
probably more applicable to keratomes with lower oscillation rates.
Similarly, flat corneas may result in a thin and/or small flap as they
could be below the adequate cutting level in certain locations.
Inadequate blade to cornea coupling is often due to poor suction
(sunken globe/small diameter corneas with inadequate suction ring
placement, conjunctival incarceration in the suction port…). Non-angled
blades have equal chances of moving upwards towards the surface or
downwards towards the stromal side if faced with resistance. On the
other hand, inferiorly angled blades are more likely to be driven
towards the stroma.
If a buttonhole is encountered (especially centrally), most surgeons
prefer to abort the procedure, replace the flap and recut a deeper flap
(20-60 ?m deeper) approximately 10-12 weeks later. While some advocate
proceeding with scraping the epithelium and performing a PRK laser
ablation, we believe this approach may not be feasible in higher myopes
due to the appearance of unexpected haze. A higher index for epithelial
ingrowth should maintained around the margins of the buttonhole.
The incidence of perforated flaps (as well as thin and irregular ones)
may be reduced if the surgeon ensures adequate suction, inspects the
blades and adjusts the keratome plate thickness according to corneal
curvature. Other helpful measures include ensuring adequate intraocular
pressure before cutting the flap. Measurement may be most valuable with
a pneumotonometer as other means were reported to provide imprecise
readings at times. Care should be taken to avoid conjunctival clogging
in the suction port, which could lead to discrepancy between the
intraocular pressure and the suction pressure recorded on the
microkeratome vacuum console. Newer microkeratomes have a safety
mechanism to automatically abort the procedure or to activate
additional suction but are also prone to similar problems if IOP
measurements are not obtained to ensure adequate suction.
Some surgeons inspect the microkeratome blade under the operating
microscope before engaging it in the suction ring in order to rule out
manufacturing or other preoperative damage to the blade. It is best to
keep the microkeratome away from hard surfaces after assembly to avoid
subsequent blade damage.
Author Bio:
Adapted from: “101 Pearls in Refractive, Cataract and Corneal Surgery”
Samir Melki MD PhD and Dimitri T. Azar MD editors, Slack inc.
www.slackinc.com Dr. Melki is a experienced Boston
affordable LASIK surgeon, Laser Eye Surgery, Vision Correction and Cosmetic
Surgery
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