SMILE put under the microscope

The relative advantages of small-incision lenticule extraction (SMILE®) over LASIK were brought under scrutiny in a debate held at the 23rd ESCRS Winter Meeting in Athens, Greece. Dimitrios Kyroudis MD took up the cudgel for LASIK, maintaining that its proven track record and only contradictory evidence supporting any superiority of SMILE in terms of visual outcomes or refractive stability, means that LASIK is the laser corneal refractive procedure of choice. SMILE was developed as a way of preserving the cornea’s biomechanical stability in order to prevent keratectasia while at the same time avoiding flap complications, diffuse lamellar keratitis and epithelial ingrowth. However, SMILE has its own, different set of complications, said Dr Kyroudis, Zurich, Switzerland. For example, obstructions to the laser beam on the ocular surface – from meibomian secretions in the tear film to ink used to mark the cornea – can prevent the laser energy from reaching the target stromal layer. The result can be difficult tissue separation, damage to the stromal bed and delayed visual recovery. Other complications can include loss of suction, which can require aborting and restarting the procedure, and retention of lenticule fragments, which can necessitate a second operation, without which the patient will have severe irregular astigmatism. Taking the opposing view, Konstantinos Moschou MD, Thessaloniki, Greece, maintained that there is adequate evidence to support SMILE’s efficacy and its superiority in some respects to LASIK. He noted over the past 10 years or so, more than 1.5 million eyes have undergone SMILE. There are 850 clinics worldwide in 70 countries where 1,700 surgeons can perform the procedure. Furthermore, SMILE was approved by FDA in 2016 and there have been more than 500 peer-reviewed studies published on the technique. He noted that SMILE has an inherent advantage over LASIK in that the femtosecond laser machine is less dependent on environmental conditions than the excimer laser. In addition, SMILE is less demanding than LASIK in terms of centration due to its larger optical zone than any excimer ablation profile. This results in less spherical aberrations. He added that whereas PRK and LASIK remove the shallower, stronger anterior stroma, SMILE removes deeper, weaker posterior stroma. That protects the eye from the development of ectasia. There are only four case-reports of ectasia published and, of those, three had infra-clinical preoperative keratoconus. “In conclusion, with SMILE we have better biomechanical stability, fewer higher-order aberrations and less dry eye symptoms,” Dr Moschou said. Dimitrios Kyroudis: dkyroudis@gmail.com

Tags: LASIK, SMILE