LASIK Flap Buttonhole Management
LASIK flap buttonholes are an uncommon intraoperative complication that can occur during flap creation for LASIK. Flap buttonholes are caused by an abnormal lamellar cut during the creation of the LASIK flap. Performing an excimer laser ablation treatment in this setting can result in an irregular corneal surface and possibly loss of correctable visual acuity due to a flap-stromal bed contour mismatch.
- 1 Disease Entity
- 2 Diagnosis
- 3 Management
- 4 References
LASIK Flap Buttonhole
Flap buttonholes are caused by an abnormal lamellar cut during the creation of the LASIK flap where there is a connection between the flap interface and the corneal surface.
Flap buttonholes are caused by an abnormal lamellar cut during LASIK flap creation with either microkeratome or a femtosecond laser.
Preoperative risk factors include steep mean corneal curvature (K >46.00 D), previous ocular surgery, and attempted creation of thin flaps (≤100 µm).Any reduction in the intraocular pressure, loss of suction, power decrease in the microkeratome motor, or blade imperfections during passage of the microkeratome increases the risk for a buttonhole or a thin flap. Incidence has been noted to be higher in the left (second) eye treated with microkeratome-assisted flaps.
Vertical gas breakthrough when using a femtosecond laser for flap creation should be considered similar to a buttonhole. Risk factors for vertical gas breakthrough when using a femtosecond laser include corneal scars or breaks in Bowman’s membrane and attempted thin flap (≤100 µm) creation.
Irregular flap cuts can lead to deceased best spectacle corrected visual acuity, glare, haloes, and diplopia, but in general rarely lead to significant visual loss or a change in refractive error unless the surgeon proceeds with the ablation.
If a keratectomy has an irregular surface, no matter how irregular the surface might be, there is a perfect match in the underside of the flap. Therefore, if the flap is simply replaced the patient should return to the preoperative refraction and best corrected visual acuity. Problems arise when the bed is altered with an attempted ablation such that the flap no longer matches the underlying stroma. This mismatch can lead to loss of correctable acuity.
Screening for risk factors such as steep corneas, previous ocular surgery, and avoiding the creation of thin flaps may reduce the incidence of buttonholes. Steep corneas have been described as being at higher risk for buttonholes as an increased amount of tissue is compressed by the microkeratome and buckling of this tissue may lead to an irregular cut. Using a smaller ring or a femtosecond laser in these eyes may decrease such risk. Using a new microkeratome blade on the second eye should be considered if the flap measurement of the first eye is noted to be thin. Surface ablation should also be considered in these eyes with high keratometry values and prior corneal surgeries.
Femtosecond laser technology for creation of the lamellar keratectomy may reduce the incidence of flap buttonholes. However, femtosecond laser-assisted keratectomy buttonholes have been associated with thin flaps (≤100 µm), previous scars, epithelial plugs, or corneal facets through which subepithelial gaseous byproducts can escape, or when a rough flap dissection is performed.
Given the innate risks of lamellar surgery, it is important to prepare the patient for a potential flap complication prior to surgery. The patient should be informed preoperatively that a flap complication can occur and that in the event of an irregular flap, no laser ablation will be performed. This preparation will prevent the patient from panicking in the event of a flap abnormality and reduces the pressure on the surgeon to proceed with an ablation that may not be appropriate.
Diagnosis is usually made intraoperatively by the surgeon noticing an area of irregularity in the flap or stromal bed surface immediately after flap creation or after the flap is lifted.
It is important for the surgeon to be aware of prior ocular surgeries. When using a femtosecond laser for flap creation, the surgeon may want to ask about prior ocular trauma or surgeries that may have lead to breaks in Bowman’s membrane such as prior radial keratotomy, astigmatic incisions, pterygium, or foreign body removals.
The flap buttonhole is evident immediately after the microkeratome has completed the reverse pass. This will generally appear as a circular area of irregularity representing the area of buttonhole. If the flap is lifted, the stromal bed should have a corresponding area of elevation that appears smooth representing the uncut area of cornea where epithelium may still be present. A corresponding divot should be seen on the under-surface of the flap.
In femtosecond assisted flap creation the surgeon may see an area of clearing among the advancing raster pattern or a bubble of air within the treatment cone-corneal surface interface. The surgeon should stop the flap creation, if possible, prior to the creation of the corneal flap side cuts.
Irregular flap cuts can lead to deceased best spectacle corrected visual acuity, glare, halos, and diplopia, but in general rarely lead to significant visual loss or a change in refractive error unless the surgeon proceeds with the ablation. Most patients return to their preoperative visual acuity and may be treated at a later date.
Patients that undergo excimer ablation despite a flap buttonhole may develop a decrease in their best spectacle correction, glare, halos, diplopia, and light sensitivity.
The diagnosis is generally made intraoperatively immediately following flap creation or during lifting of the flap.
Corneal topography postoperatively may reveal an area of irregularity at the area of buttonhole that should improve with time.
Epithelial defect, epithelial basement membrane dystrophy, corneal scar, flap tear.
If a flap buttonhole is noticed prior to lifting the flap and the flap appears adequately positioned, the flap should not be lifted, and a bandage contact lens should be placed to assist flap adhesion. If the surgeon is unsure if a buttonhole exists, flap lift can be attempted with care not to poke the spatula through the area of the buttonhole and tear the flap further with the spatula. If the flap is lifted and the buttonhole confirmed, it should be meticulously repositioned and a bandage lens placed over the flap. If the flap is lifted it can generally be meticulously replaced without sequelae. Some surgeons advocate removing the epithelium in the area of the buttonhole in order to decrease the risk of epithelial ingrowth into the affected area, however, manipulation of this already thin area may lead to further complications. A bandage contact lens should be placed for 3-7 days in order to secure the flap into position.
In femtosecond assisted flap creation, the surgeon may notice vertical gas breakthrough during the raster pattern portion of the procedure. The surgeon should stop the flap construction, if possible, prior to the creation of the epithelial and Bowman’s membrane sidecuts. In this manner, the potential flap is maintained in the original confirmation and, if it is not lifted, the patient’s cornea should essentially return to its preoperative status in a few days. If the flap is lifted, the above recommendations used for microkeratome lift also apply.
Glasses or contact lenses may be used to correct refractive error or anisometropia while the flap heals.
Medical follow up
Several methods to managing buttonholes have been proposed. A repeat cut using a thicker flap (in general at least 20-60 µm deeper) can be considered if the flap was thin and the cornea is thick enough to undergo treatment. Surface ablation procedures such as photorefractive keratectomy (PRK) or laser assisted sub-epithelial keratomileusis (LASEK) can also be performed after the lamellar cut has healed. A no-touch surface ablation technique may be beneficial in these cases by reducing the chance of flap slippage during the procedure. Although immediate trans-epithelial PRK has been described, this technique is not recommended by the majority of surgeons.
Surgical follow up
Follow up for these patients should be done on a case-by-case basis, depending on the appearance and size of the buttonhole. The surgeon should monitor for scarring or epithelial ingrowth in the area of the buttonhole that may preclude a good outcome despite retreatment. If these complications occur, treatment should first be focused on preventing scarring that may preclude a good outcome with a second refractive procedure.
Surfacing of the blade or gas escape through the central corneal flap can lead to scarring or epithelial ingrowth into the interface which may limit the ability of the surgeon to successfully repeat the LASIK procedure at a later date. The timing of treatment should be adjusted for each patient as to treat before the epithelial ingrowth becomes severe and before severe scarring occurs that may leave irregular astigmatism that may not be amenable to treatment.
In general flap buttonholes are uncommon and treatable with excellent outcomes as long as good surgeon judgment and patient education occurs at the time of such an event.
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