The European Experience with KLEx

Keratorefractive lenticule extraction (KLEx) for correcting myopic astigmatism is a safe, effective, and precise procedure that provides outcomes comparable to those associated with LASIK and PRK, said Thomas Kohnen MD, PhD.

“As a mature, flapless procedure involving a very small incision, I think that KLEx is a very intriguing option for patients seeking refractive surgery,” he commented.

Sharing an update on the European experience with KLEx, Professor Dr Kohnen said it began in 2006 with the VisuMax femtosecond laser (Carl Zeiss Meditec). SMILE using the VisuMax laser received the CE mark in 2011, and between 2020 and 2023, the CE mark was given to four additional KLEx procedures/laser platforms: CLEAR/FEMTO LDV (Ziemer), SmartSight/ATOS (Schwind), SMILE PRO/VisuMax 800 (Carl Zeiss Meditec), and SILK/ELITA (Johnson & Johnson).

Prof Dr Kohnen reviewed published literature reporting on these procedures, including a meta-analysis by German authors.¹ The investigators reviewed studies with minimum follow-up of 10 years, concluding that the results of KLEx (SMILE) are at least equivalent to PRK and LASIK, with none of the three procedures demonstrating superiority.

Prof Dr Kohnen said he performs KLEx with the ATOS laser. A preclinical study investigating its use for lenticule creation in fresh porcine eyes provided evidence that its accuracy and repeatability were comparable to already established systems.²

“This solid-state laser has a high repetition rate, low pulse energy, integrated eye tracking, cyclotorsion correction, pupil detection, and astigmatic correction,” he said. “Using it at our centre, we have found very good outcomes in the first 50 KLEx cases.”

KLEx candidates

In 2023, the German Society of Ophthalmology (DOG) Committee of Refractive Surgery published its recommendation on refractive surgical interventions that stated KLEx was appropriate for myopia correction from -1 to -8 D and astigmatism correction up to 5 D. The recommendations stated KLEx had limited application for correcting -8 to -10 D of myopia. Guidelines from the ESCRS are undergoing final revision and are expected to be published early in 2026. In agreement with the DOG recommendations, the ESCRS guidelines will recommend KLEx for treating up to -8 D myopia and 5 D astigmatism and specify that application over this limit should only be done with a regular cornea, no risk factors, and sufficient corneal thickness.

“In developing the ESCRS guidelines, we referenced a huge amount of data from the European experience, [particularly] refractive outcomes,” Prof Dr Kohnen said.

He also identified clinical scenarios that represent “special indications” for choosing KLEx when patients seek refractive surgery. Prof Dr Kohnen said KLEx is ideal for patients with thin corneas because it has minimal impact on corneal biomechanics. In addition, it could be preferred over LASIK for people who engage in contact sports for whom there is concern about trauma causing flap dislodgement. KLEx might also be a better choice than LASIK for patients with dry eye because KLEx may cause less disruption of corneal nerves. Since KLEx is performed with a large optical zone, it can also be a good option for individuals who are prone to halos and visual symptoms from spherical aberrations.

Prof Dr Kohnen spoke at AAO 2025 Refractive Surgery Subspecialty Day in Orlando, US.

Thomas Kohnen MD, PhD, FEBO is Professor and Chair of the Department of Ophthalmology, Goethe University, Frankfurt, Germany. kohnen@em.uni-frankfurt.de

1. Taneri S, et al. Ophthalmologie, 2022; 119(2): 163–169.

2. Lwowski C, et al. Transl Vis Sci Technol, 2022; 11(6): 20.

3. Berufsverband der Augenärzte Deutschlands e. V. (BVA); Deutsche Ophthalmologische Gesellschaft (DOG). Ophthalmologie, 2023; 120(6): 633–644.