Evolutions in surgery

Corneas happier with SMILE than with excimer laser procedures

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Small-incision lenticule extraction (SMILE) appears to be a step forward from LASIK in the evolution of corneal refractive surgery. This is because it has greater respect for the cornea’s biomechanical and neuronal integrity, is less traumatic to the lamellar tissue and induces a less vision-compromising healing response, asserts Leonardo Mastropasqua MD, University of G d’Annunzio, Chieti-Pescara, Italy. Although excimer laser corneal refractive procedures have advanced since their introduction, many drawbacks remain. In the case of PRK, regression and haze are still an issue. For LASIK, flap creation alone causes biomechanical changes in the cornea that can lead to ectasia and it also severs the nerves of the ocular surface, leading to dry eye and other flap-related complications, Dr Mastropasqua told the XXXV ESCRS Congress in Lisbon, Portugal. “Small-incision refractive lenticule extraction has the advantage over PRK of being intrastromal and therefore less likely to induce haze. And unlike LASIK, it is flapless and the entire procedure can be performed with the same laser,” Dr Mastropasqua said. In addition, research has shown that collagen destruction and cell damage is minimal in femtosecond laser-created lenticules in the areas adjacent to the laser cut. Studies also suggest that SMILE induces less inflammation and extracellular matrix deposition than excimer laser procedures, especially at high refractive corrections, Dr Mastropasqua said. BETTER BIOMECHANICAL STABILITY SMILE also has much less impact on biomechanical integrity than LASIK, he noted. The resistance to deformation following LASIK is dependent on the thickness of the residual stromal bed, but after SMILE the residual stromal bed starts from Bowman’s membrane. Therefore, the deformation aptitude index is only slightly modified after SMILE for high myopic correction when tested with a Scheimpflug-based non-contact tonometer. He added that in vivo findings suggest that there is significantly less nerve loss after SMILE than after flap-based techniques and that SMILE is associated with quicker nerve regeneration. This may account for reduced dry eye symptoms reported in SMILE-treated corneas. BEYOND SMILE Looking ahead, Dr Mastropasqua noted that the less traumatising impact of the femtosecond laser also allows the possibility of implanting of lenticules from other corneas for refractive correction and the treatment of keratoconus. In a trial involving 10 eyes of 10 severe keratoconus patients that he and his associates conducted, preliminary results showed that lenticule implantation induced a significant flattening of anterior corneal central areas and an increase of corneal thickness that correlated consistently with the implanted lenticules with thickness and diameter. Leonardo Mastropasqua: mastropa@unich.it
Tags: Small-incision lenticule extraction