Digitized Evaluation of Femtosecond Laser–Assisted LASIK Flap Parameter, x and y Diameter, Thickness, and Opaque Bubble Layer Extent
To determine the precision and accuracy of flap parameters (x and y diameter and thickness) in comparison to programmed settings as well as the extent of Opaque Bubble Layer (OBL) in femtosecond laser-assisted myopic LASIK. Comparative results between two centers.
Site-1 (US) 48 consecutive eyes (24 OD, 24 OS). Site-2 (GR), 36 consecutive eyes (16 OD, 20 OS). Flaps (programmed diameter 8.50-mm) were created with the FS200 femtosecond laser and were imaged digitally intra-operatively. Image processing by specially-developed software was employed to document flap diameter accuracy (vertical and horizontal) to the 100-μm sensitivity level, and OBL occurrence and extent as flap area percentage.
Additionally, 48 eyes from site-2 were investigated for 8.00-mm programmed flap diameter (24 OD, 24 OS) and central flap thickness (planned 110-μm) was measured in all site-2 eyes using anterior-segment OCT meridional scans acquired one-month postoperatively.
For 8.50-mm programmed flaps: US site-1, horizontal diameter 8.44±0.02 (8.35-to-8.45) mm, vertical 8.32±0.05 (8.24-to-8.43) mm. OBL extent was 5.48±8.25 (0.00-to-26.64) % of flap area. GR site-2, horizontal diameter 8.43±0.03 (8.39-to-8.48) mm, vertical 8.43±0.03 (8.41-to-8.49) mm. OBL extent was 5.33±7.59 (0.00-to-26.44) % of flap area.
For 8.00-mm programmed flaps (only GR site-2): Horizontal diameter 7.87±0.02 (7.84-to-7.89) mm, vertical 7.84±0.02 (7.80-to-7.85) mm. OBL extent was 4.89±7.52 (0.00-to-22.64) % of flap area. For the 110-μm thickness programmed flaps (all 84 site-2 flaps): measured central thickness 113.54±1.39 (111-to- 119) μm. Intra-flap thickness variation was under 5 μm (1-4) in all cases.
This study documents and confirms using an objective digitized analysis, that FS200-created flaps demonstrate high precision, accuracy, and reproducibility. Revised treatment parameters (venting channel dimensions, spot separation and energy settings) may offer significant reduction of clinical OBL occurrence.