Thin-flap LASIK has much less possibility of triggering inflammation and haze as compared to surface ablation
The rate of refractive enhancement after SMILE is low. If re-treatment is needed and there is sufficient tissue to safely create a flap, thin-flap LASIK is a viable option that provides excellent visual and refractive outcomes. According to an ophthalmologist. The eye doctor presented data from a retrospective study that reviewed 2,643 consecutive SMILE procedures performed between September 2013 and January 2016. A total of 116 (4.4%) eyes underwent re-treatment, of which 100 were with LASIK. Flaps, created using a femtosecond laser (VisuMax, Carl Zeiss Meditec), were ≤110 μm in all but three eyes. The attempted SEQ for the eyes re-treated with LASIK ranged from –1.88 to +1.50 D (mean –0.05 ± 0.99 D) and the mean cylinder was -0.70 ± 0.55 D. Postoperatively, mean SEQ relative to the target was +0.19 ±0.49 D, the refractive outcome was within ±0.5 D of target in three-fourths of eyes, and mean cylinder was –0.29 ± 0.24 D. Eighty-one percent of eyes achieved uncorrected distance visual acuity of 20/20 or better, up from 11% before the re-treatment and relative to 95% of eyes with corrected distance visual acuity of 20/20 or better. No eyes lost ≥2 lines of corrected distance visual acuity, and only one eye lost 1 line. “Initially, it was thought that only surface ablation could be done for eyes needing retreatment after SMILE, and then techniques were developed to convert the SMILE cap interface into a LASIK flap by performing a side cut or Circle procedure.” “The advantages of doing thin flap LASIK are that it has less chance of causing inflammation and haze compared with surface ablation, and compared with converting the SMILE cap interface into a LASIK flap, it leaves a greater amount of uncut stromal fibres and therefore causes less biomechanical weakening if the original SMILE cap was relatively thick.
PLANNING AND TECHNIQUE
In order to perform thin-flap LASIK, there must be sufficient space between the epithelium and the SMILE cap to safely create the flap. Making that determination requires the ability to visualize the full cap and epithelial thickness and obtain accurate measurements of the distance between the maximum epithelium thickness and the minimum cap thickness. Either very high-frequency digital ultrasound (Artemis Insight 100, ArcScan) or anterior segment optical coherence tomography (e.g., RTVue, Optovue) can be used for the anatomical evaluation. Providing some general rules, opthalomalogists believe that, “A thin LASIK flap can be created if there is at least 40 μm between the maximum epithelium thickness and minimum cap thickness. Therefore, assuming an average epithelial thickness profile after SMILE, a 90-μm flap can almost always be created in an eye that had a 120-μm SMILE cap.” The approach for lifting the flap has also evolved over time. The majority of cases were done using the bimanual inferior pseudo-hinge fulcrum technique, which was designed to reduce the risk of entering the small incision and creating a tear or accessing the original SMILE interface. He noted that SMILE interface access or an incision tear occurred in 10 (7.2%) of the 139 procedures. There were no intra-operative complications in the 84 consecutive cases that were done using the most recent iteration of the flap lift technique. The technique or method involves inserting the flap lifter and McPherson’s forceps in the inferior third of the flap. Upward pressure is applied while pushing the instrument across the interface in order to prevent the instrument from breaking through to the SMILE interface. While holding one instrument at the hinge to provide counterforce, the second instrument is used to separate the inferior third of the interface towards the hinge. The rest of the separation and flap lift can be completed using a standard technique. U.S. surgeons will have to make a few small changes to this technique to account for the current software restrictions on incision size and location according to the panel of ophthalmologists.