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Buttonholed Flaps and Vertical Gas Breakthrough
ETIOLOGY AND INCIDENCE OF BUTTONHOLED FLAPS AND VERTICAL GAS BREAKTHROUGH
Femtosecond LASIK
Cavitation bubbles from the femtosecond laser can dissect upwards toward the epithelium and are called vertical bubble breaks.1–3 The bubbles may either stay below Bowman’s membrane or break through the epithelium. When the bubbles stay under Bowman’s layer, a focal thinning in the flap is noted. If the break is through the epithelium, this is considered a buttonhole.
The following 2 types of bubbles have been described:
- Partial bubble breaks characterized by a gray/white appearance.
- Full breaks characterized by a deep black appearance. They are thought to occur due to the dissection of cavitation bubbles into the subepithelial space.
Risk factors include corneal scars, microscopic breaks in Bowman’s membrane, and thin flaps, which can lead to accidental vertical gas breakthrough (VGB). Reported VGB incidence varies between 0% with the 60 kilohertz (kHz) femtosecond laser (IntraLase [Abbott Medical Optics]) and 1.3% with Femto LDV (Ziemer Ophthalmic Systems).4,5
Microkeratome LASIK
A buttonholed flap occurs when the microkeratome blade travels more superficially than intended and enters the epithelium/Bowman’s complex. Buttonholes may be partial thickness if they transect Bowman’s layer or full thickness if they exit through the epithelium. The incidence of buttonholes ranges between 0.2% and 0.56%.1,6 No clear etiology has been identified for this complication. Presumed risk factors include the following:
- High keratometric values, although this is not consistent with our experience.
- Previous incisional keratotomy.
- Pre-existing surface lesion (eg, pterygium, corneal scars).
FEMTOSECOND LASIK COMPLICATIONS AND IMMEDIATE SOLUTIONS
Complication #1: Black Vertical Gas Breakthrough in Visual Axis
Video section: 1 minute 58 seconds
Platform: IntraLase FS60 (kHz) (Abbott Medical Optics)
Flap diameter: 9.3 mm
Flap target depth: 100 microns (µm)
The initial surgery on the right eye resulted in black VGB in the visual axis (video 4; time: 1 minute 58 seconds; Figures 4-1, 4-2, and 4-3).
Some practical measures are as follows:
- Continue the femtosecond laser treatment to avoid a partial flap.
- Assess the position of the VGB within the flap.
- The flap with black VGB affecting the visual axis should not be lifted and surgery should be aborted.
Figure 4-1. Initial surgery resulted in black VGB in the visual axis (red arrow).
Figure 4-2. Photograph showing black VGB in the visual axis (red arrow).
Figure 4-3. Photograph showing black VGB in the visual axis (red arrow). Surgery was aborted. Surgery in the fellow eye was uneventful. One month later, the right eye underwent LASIK surgery. At the 2-month follow-up visit, uncorrected distance visual acuity was 20/20 in each eye.
Figure 4-4. Initial surgery resulted in white/gray VGB in the para central pupillary area (red arrow). Figure 4-5. Photograph showing white/gray VGB in the para central pupillary area (red arrow). Complication #2: White/Gray Paracentral Vertical Gas Breakthrough Video section: 2 minutes 10 seconds Platform: IntraLase FS60 kHz Flap diameter: 9.3 mm Flap target depth: 100 µm The initial surgery on the right eye resulted in white/gray para central pupillary VGB (video 4; time: 2 minutes 10 seconds; Figures 4-4, 4-5, and 4-6). Figure 4-6. Flap lift did not result in a full-thickness buttonhole (red arrow) (see Figure 4-15). Excimer laser treatment was uneventful. Surgery was uneventful in the fellow eye.
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