A new technique for performing retreatments in small incision lenticule extraction (SMILE) cases appears to be both safe and efficacious in initial clinical studies, according to David Donate MD.
“While we clearly need a lot more patients and longer follow-up, early results with this new approach indicate that enhancements after primary SMILE procedures to eliminate residual refractive myopic error are feasible,” Dr Donate told EuroTimes.
The new approach to SMILE enhancements is called “sub-cap-lenticule-extraction” (sub-cap-LE), explained Dr Donate, who is in private practice in Lyon, France. “The aim is to leave the cap of the primary SMILE procedure untouched in order to conserve the benefits associated with SMILE. No new superior lenticule is cut to avoid the risk of a multiple dissection plane. The interface of the primary SMILE procedure then becomes the superior plane of the new lenticule, and the laser is used to create only the inferior plane and sidecut of the new lenticule. Once this has been achieved, the surgeon stops the ablation and the new lenticule is removed through the original corneal incision,” he said.
Dr Donate’s original report of sub-cap-LE included a single case presentation of a successful use of the technique in a 53-year-old woman who experienced blurred distance vision after bilateral SMILE for correction of moderate myopia. The same technique has now been used in a series of 12 eyes with similarly successful results, he said.
While the appeal of flapless refractive surgery has encouraged many surgeons to try SMILE in recent years, one of the frequently cited drawbacks of the procedure was the lack of an efficient and safe retreatment method.
Although photorefractive keratectomy (PRK) offers a viable means of correcting residual refraction after SMILE, issues such as pain, slow recovery and postoperative haze make it a less than optimal solution.
Carl Zeiss Meditec has also sought to address the issue by developing an option within the VisuMax platform to create a corneal flap after previous refractive correction with SMILE. This approach uses the laser to create four circle patterns that enable the original SMILE incision pocket to be converted into a LASIK-like flap that can be easily lifted to allow for stromal ablation of the residual refractive error with an excimer laser.
Another safe and effective method of retreating after SMILE is to perform a thin-flap LASIK procedure. This is the approach preferred by Dan Z Reinstein MD, FRCSC, FRCOphth, FEBO, who was one of the early adopters of SMILE in his London clinic.
“My protocol is to use a cap thickness of at least 135 microns for the primary SMILE procedure, something that we want to do anyway in order to take advantage of leaving the stronger anterior stroma and nerve plexus untouched. We know that the epithelium will have thickened centrally after a myopic correction to partially compensate for the tissue that has been removed, but we also know that the epithelium will not be thicker than about 80 microns. Therefore, we have a gap between 80 microns and 135 microns in which to make a flap,” Dr Reinstein told EuroTimes.
This leaves a more than sufficient safety margin to perform a thin-flap LASIK procedure, said Dr Reinstein.
“Given that the standard deviation of flap thickness with the VisuMax is 4.4 microns, if we aim for a 100-micron flap, then the flap will be more than four standard deviations away from both the epithelium and the existing SMILE interface, even if the SMILE interface was more superficial than intended. In reality, we are even safer than this because we measure both the epithelial thickness and SMILE cap thickness by optical coherence tomography (OCT) and very high-frequency digital ultrasound, so we can plan the flap thickness to use based on direct measurements,” he said.
While the method works very well, Dr Reinstein said the new technique proposed by Dr Donate is something that will definitely interest a lot of surgeons.
“If the results continue to be as promising as the initial case report by Dr Donate, then this may well become the standard method for retreatments after SMILE,” he said.
Dan Z Reinstein: firstname.lastname@example.org