Objective Evaluation of Novel Femtosecond Laser Flap Parameters in Opaque Bubble Layer Incidence: Digital Analysis
Narrative Responses:
Purpose
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 digital image analysis in comparison to two different patient interfaces and novel flap parameter settings.
Methods
Digital images from 100 flaps recorded during routine LASIK procedure assisted with the FS200 femtosecond laser (Alcon Surgical Fort Worth, TX). We investigated possible bias on the 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, of 50 flaps created with a metal-and-glass patient interface and group B, of 50 flaps with a molded plastic interface.
Correlation between the achieved and indented flap diameter was assessed using paired two-tailed t-tests, coefficient of determination (R2), trend line linearity, bias, and plots of differences against means.
Results
The indented flap diameters ranged 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 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. The comparison between the two patient interfaces showed no statistical significant difference.
Conclusion
The FS200 created flaps have excellent reproducibility. Very small deviations from the indented diameter are observed. OBL incidence was, for the majority of the flaps less than 3% of the total area. The newly-introduced patient interface showed interchangeable results.