Possible risk factors and clinical effects of an opaque bubble layer created with femtosecond laser–assisted laser in situ keratomileusis

Purpose To report the risk factors and clinical effects of an opaque bubble layer (OBL) during creation of a laser in situ keratomileusis (LASIK) flap with the Visumax 500 kHz femtosecond laser. Setting HanGil Eye Hospital, Incheon, South Korea. Design Retrospective comparative study. Methods Visual acuity, manifest refraction, intraocular pressure, corneal curvature, corneal thickness, and optical quality were evaluated. To prove a previous hypothesis that the harder a surgeon applanates during flap creation (hard-docking technique), the higher the incidence of OBL, the area of the meniscus on the cornea to which pressure was applied by the patient interface was calculated. Eyes were separated into 2 groups; that is, OBL-occurrence group and OBL-free group. Clinical outcomes in the 2 groups were compared to measure the risk factors and clinical effects of an OBL. Results The study included 827 myopic eyes. The incidence of OBL was 5.0% (41 eyes). The mean flat keratometry was steeper and the preoperative cornea thicker in the OBL-occurrence group. The OBL-occurrence group had harder applanation (ie, a larger area of meniscus) than the OBL-free group. The incidence of OBL was higher in the hard-docking technique. Clinical outcomes, including refractive error, visual acuity, and optical quality, in the 2 groups were not statistically significantly different 1 month after LASIK. Conclusions The incidence of OBL was 5.0%. A steep, thick cornea and a hard-docking technique could be risk factors for an OBL. The OBL did not appear to affect optical quality or visual outcomes. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.