Biomechanical Changes Pre- and Post-Flapless Femto Refractive Procedure and Femto-LASIK by Assessment of Corneal Deformation Response
Narrative Responses:
Purpose
To evaluate and compare corneal deformation amplitude in patients prior to and following small incision lenticule extraction (SMILE) and Femtosecond laser in situ keratomileusis (Femto-LASIK) using Non-Contact-Tonometer with visualization and measurement of the corneal deformation response to an air pulse with an Ultra-High-Speed Scheimpflug camera.
Methods
prospective, comparative study, 20 patients 40 eyes divided into 2 groups. Corneal Deformation amplitude was recorded using (Corvis®ST) prior to and 3 months after corneal laser refractive surgery for myopia. Preoperative corneal deformation amplitude was correlated with age and preoperative central corneal thickness (CCT). Postoperative corneal deformation amplitude was correlated with postoperative CCT in both treatment groups. The correlations between postoperative change in deformation amplitude and stromal ablation/removal depth, percentage of tissue ablated/removed, optical zone and patient age were also examined. The femtosecond laser platform used for SMILE and for flap creation was the Visumax 500 and the eximer laser platform was ALLEGRETTO excimer laser.
Results
A total of 40 eyes of 20 patients were involved in the study. Femto lasik was performed in 20 eyes and SMILE in 20. Mean preoperative corneal deformation amplitude of all eyes was 0.97 ±0.15 mm. Mean age, preoperative CCT, corneal deformation amplitude and ablation/tissue removal profile were similar in both groups. A statistically significant increase in deformation amplitude occurred following Femto-LASIK of 18.9% ±3 and on the contrary the smile group showed an increase of 4.7%±2. A weak correlation was found between postoperative decrease in deformation amplitude and the parameters examined.
Conclusion
Corneal deformation amplitude increased following Femto-LASIK is much more significant in comparison with the smile group. Postoperative deformation amplitude increase did not correlate with the amount or percentage of corneal tissue removed, nor with optical zone or patient age.