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Siddarth Rathi, Anastasios J Kanellopoulos, George Asimellis; Femtosecond laser flap parameters and opaque bubble layer incidence: a novel digital analysis technique. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1528.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the extent and rate of incidence on opaque bubble layer (OBL) and to determine femto-second laser assisted corneal flap diameter accuracy and precision by a novel digital image analysis.
Digital images from 100 flaps captured during routine LASIK procedures with the FS200 femtosecond laser (Alcon Surgical, Fort Worth, TX). They were objectively analyzed for flap size (diameter) by comparing achieved vs intended (programmed) diameter and investigated OBL incidence and extent (area). Two groups of study were formed: group-A and group-B, of 50 flaps of different laser flap parameters (A vs B: increased venting chimney diameter and decreased spot separation). Statistics were assessed using paired two-tailed t-tests, coefficient of determination (R2), trend line linearity, bias, and plots of differences against means.
The indented flap diameters ranged in both groups from 8.00 to 9.50 mm. The achieved flap diameter was on average -0.16 mm smaller for the programmed 8.00 mm, -0.12 mm for the 8.50 mm, and +0.03 mm larger for the 9.50 mm programmed diameter. With an average flap area 72.4±9.5 mm2, the average OBL area in group-B was 4.1±4.3 mm2 (14.34 to 0 mm2), corresponding to a 6% OBL-to-flap area. 30% of the flaps had zero, and 50% had OBL area corresponding to less than 2.7% of the total flap area. In group-A, respectively, the OBL-to-flap area was 2.9±2.3 mm2, corresponding to a 3.5% OBL-to-flap area.
The FS200 created flaps have impressive reproducibility. Very small consistent deviations from the indented diameter are observed. OBL incidence was, for the majority of the flaps less than 3% of the total area in group-A (improved parameter settings).
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