Changes In Corneal Asphericity, Spherical Aberration And Effective Optical Zone After Lenticule Extraction Surgery With A Low Energy Femto Ldv Z8 Clear Utilising An Individualized Aspheric Treatment Profile.

To evaluate changes in corneal asphericity (characterized by Q-value), induced spherical aberration (SA) and effective optical zone (EOZ) after Corneal Lenticule Extraction for Advanced Refractive Correction (CLEAR).

A retrospective, single-surgeon, consecutive case-series study. All patients underwent CLEAR surgery in Silmäsairaala Pilke Eye Clinic in Tampere, Finland.

Postoperative changes in Q-value, induced SA and EOZ measured on the tangential curvature difference map generated by the Scheimpflug tomography system (Galilei G6 ColorZ, Ziemer Ophthalmic Systems AG, Switzerland) in patients treated with the low energy FEMTO LDV Z8 CLEAR application (Ziemer Ophthalmic Systems AG) to correct myopia or compound myopic astigmatism, were evaluated at 3 months after the surgery.

Sixty eyes of 30 patients with mean age 31.30 ± 4.77 years and mean preoperative spherical equivalent refraction (SEQ) of -3.15 ± 1.69 dioptres (D) were included. The mean positive increase of Q-value (oblate shift) after the surgery was +0.14 ± 0.25. No significant postoperative induction of SA was observed in the entire dataset. The mean programmed optical zone (POZ) was 6.50 ± 0.00 mm and the mean EOZ after CLEAR surgery was 5.93 ± 0.40 mm. A very strong, statistically significant, positive linear correlation between the change in Q-value and the induced SA was observed (r = 0.865; p < 0.001) and a moderate, significant negative correlation was found between the change in Q-value and the EOZ reduction (r = -0.519 ; p < 0.001).

In corneal laser ablation surgery aspheric algorithms were designed to compensate for the spherical aberration induced by standard ablation profiles, which led to an improved visual outcome. The CLEAR application for lenticule extraction surgery includes an individualized aspheric treatment profile with target asphericity set at the preoperative Q-value. In this study, after CLEAR surgery, minimal changes in corneal asphericity, limited induction of SA and little reduction of EOZ were observed. The individualized aspheric femtosecond laser treatment profile implemented in the CLEAR application seems to be effective in preserving a preoperative anterior corneal surface asphericity.