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ETIOLOGY AND INCIDENCE OF OPAQUE BUBBLE LAYER
Opaque bubble layer (OBL) varies in incidence depending on the particular femtosecond laser that is used. Some femtosecond laser systems have programs that create a decompression pocket or channel that facilitates gas escape during the raster pass.1–3 In some cases, gas can still collect in the stroma and lead to an OBL.1–3
Cavitation bubbles formed during flap creation can expand into a cleavage plane at the stromal interlamellar space, which connects to the surface via the side cut. It is hypothesized that when the laser energy is too high (causing excessive bubbles) or too low (resulting in an inadequate pocket to vent the bubbles), microplasma bubbles can travel in errant directions, push apart collagen fibrils around them, and expand into the created space.4 This is especially true in cases where the pocket/channel is turned off and no meniscus is present.4 It is also thought that older patients have denser collagen in the peripheral cornea and sclera compared with younger patients, which may not allow bubbles to exit the periphery.4 Steeper, thicker corneas, small flap, and hard-docking technique have been associated with more OBLs.4
Reported OBL incidence varies between 3.69% on WaveLight FS200 (Alcon Labs) and 52.5% on IntraLase FS60 kilohertz (kHz) (Abbott Medical Optics).5 Studies using the IntraLase 60 kHz femtosecond laser found that 52.5% developed an OBL of various severities.5 Forty percent were with a hard pattern, and 12.5% were with a soft pattern (under pocket-on mode).5–8 Studies on eyes undergoing WaveLight FS200 femtosecond LASIK found an average of 3.69% OBL in the flap area in the group with 1.7 mm channel length and 6.06% OBL in the group with 1.3 mm channel length.6 Studies on the VisuMax 500 kHz femtosecond laser (Carl Zeiss Meditec Inc) shows that the incidence of OBL was 5%. Studies on FEMTO LDV Z6 (Ziemer Ophthalmic Systems) shows that the incidence of OBL was 2%.9
FEMTOSECOND LASIK COMPLICATIONS AND IMMEDIATE SOLUTIONS
Complication #1: Opaque Bubble Layer in Visual Axis
Video section: 1 minute 5 seconds
Platform: IntraLase FS60 kHz
Flap diameter: 9.3 mm
Flap target depth: 100 microns (µm)
The initial surgery resulted in OBL reaching the visual axis (video 5; time: 1 minute 5 seconds; Figures 5-1, 5-2, and 5-3).
Some practical measures are as follows:
- Downward pressure with a spatula over the involved area after flap lifting may facilitate tracker registration and pachymetry measurement.
Figure 5-1. Initial surgery resulted in OBL in the pupillary area (red arrow).
Figure 5-2. Downward pressure with a spatula over the involved stromal area was exerted to express the air out and to facilitate tracker registration and pachymetry measurement.
Figure 5-3. Excimer laser treatment (VISX STAR S4 [Abbott Medical Optics]) was then uneventful.
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