Two Femtosecond Laser LASIK Platforms: Comparison of Evolution of Visual Acuity, Flap Thickness, and Stromal Optical Density

Abstract

Purpose: To compare postoperative evolution of visual acuity, flap thickness, and stromal optical density during the first 3 months after femtosecond (FS) laser in situ keratomileusis surgery for correction of myopia using the iFS 150-kHz FS laser and LenSx FS laser platforms. Methods: This was a prospective case series. Thirty-nine eyes treated with the iFS 150-kHz FS laser versus 38 refraction-matched eyes treated with the LenSx FS laser platform were included. Visual outcomes, flap morphology, and optical density of the stroma (in both flap and residual stromal bed) were compared at 4 visits during a three-month follow-up period. Results: No significant differences were found in uncorrected distance visual acuity in any of the follow-up visits (1 day −0.02 vs. −0.03; 1 week −0.04 vs. −0.03; 1 month −0.04 vs. −0.04; 3 months −0.03 vs. −0.05 logarithm of the minimum angle of resolution). Flaps created with the iFS 150-kHz FS laser were closer to the intended thickness (110 μm) in every postoperative comparison (1 day 108.6 vs. 124.3; 1 week 107.6 vs. 123.6; 1 month 110.4 vs. 126.8; 3 months 116.2 vs. 126.5 μm; P < 0.0001). Dispersion of values, standard deviation, intraflap range, and differences in symmetric points were lower in the iFS 150-kHz FS laser group. Flap stromal optical density was significantly higher in the LenSx FS laser group at day 1 and week 1 (134.5 vs. 158.9 gray scale unit [GSU]; P < 0.0001 and 144.8 vs. 160.1 GSU; P = 0.011, respectively). Residual stromal bed optical density was higher in the LenSx FS laser group at all postoperative visits, and the differences reached significance at 1 week postoperatively (121.9 vs. 135.4 GSU; P = 0.03). Conclusions: Although both devices provided satisfactory visual outcomes, significant differences were detected in flap parameters. Flaps made with the iFS 150-kHz FS laser were thinner, more uniform, transparent, and accurate compared with those obtained with the LenSx FS laser.

The Impact of Learning Curve on Flap Thickness Outcome in Femtosecond Laser-assisted Laser In Situ Keratomileusis Performed with New LenSx Dual Platform

“…Notably, data from a past study among experienced and novice LASIK surgeons indicated a fellowship-training program based on a standardized surgical protocol to result in statistically comparable outcomes between an expert surgeon and a fellowship-trained surgeon when newly transitioned from mechanical microkeratome to a FS laser flap creation. [20] However, it should be noted that, while FS laser-created LASIK flap has been reported to be a uniform flap that may contribute to more predictable refractive and wavefront outcomes, [5,9,21] the clinical relevance of FS laser is considered to remain controversial. [5,19] In a past study comparing iFS 150-kHz vs. LenSx FS lasers in correction myopia, authors reported association of iFS 150 kHz with significantly lower intra-FT range at…”

“…[ [3][4][5] Thus, the technological evolution of flap creation has emerged from manually guided mechanical microkeratomes to automated microkeratomes, single-use microkeratomes, and most recently to femtosecond (FS) laser technology. [3,6,7] In 2015, a new software program was installed to the original software of the LenSx FS laser to perform LASIK flaps via the same FS laser previously used for cataract surgery.…”

“…This theoretically allows for better approximation of the contour of the cornea, enabling an easier docking process while requiring less suction and minimizing corneal compression and distortion with less elevation in intraocular pressure (IOP), and it is therefore easier for the patient to maintain fixation while the suction ring is seated. [5,8] Although the perceived benefits are promising in terms of good visual outcomes and acceptable flap thickness predictability, there is limited published evidence regarding the corneal flap morphology outcome of the dual LenSx FS laser (Alcon Laboratories, Inc, Aliso Viejo, CA) device using curved applanation cone. [5,9] Indeed, the learning curve of surgeons, and the lack of sufficient data on safety profiles of FS laser technology overall, not only for the new LenSx dual platform, are considered amongst the major barriers in use of FS lasers for LASIK in real-life clinical practice.…”

“…[5,8] Although the perceived benefits are promising in terms of good visual outcomes and acceptable flap thickness predictability, there is limited published evidence regarding the corneal flap morphology outcome of the dual LenSx FS laser (Alcon Laboratories, Inc, Aliso Viejo, CA) device using curved applanation cone. [5,9] Indeed, the learning curve of surgeons, and the lack of sufficient data on safety profiles of FS laser technology overall, not only for the new LenSx dual platform, are considered amongst the major barriers in use of FS lasers for LASIK in real-life clinical practice. [10] Notably, moistness status of the contact surface is of critical importance in using the curved applanation cone.…”

“…However, in case of insufficient moisturization epithelial wrinkles may occur, which negatively impacts the focus of laser Learning curve in FS-LASIK with curved cone 4 beams and flap quality. [5,11] Hence, although the transition is easy for existing FS laser-assisted LASIK surgeons, there is a short learning curve for optimization of the contact surface. We aimed to evaluate the effect of this learning curve on flap thickness using the anterior segment optical coherence tomography (AS-OCT), considered a reliable method for assessing flap thickness parameters in LASIK for the cornea.…”