Enhancement Options After Myopic Small-Incision Lenticule Extraction (SMILE): A Review

Abstract

Purpose:To provide an overview of the currently available retreatment methods after myopic small-incision lenticule extraction (SMILE).Design:Systematic literature review.Methods:The PubMed library was searched for articles containing the terms “small-incision lenticule extraction” and “enhancement” or “retreatment”. The last search was performed on May 1, 2019.Results:In contrast to laser in-situ keratomileusis (LASIK), which can be retreated by a flap relift, repeat SMILE retreatment is currently not approved and only seldomly performed. As substitutes, surface ablation, cap-to-flap conversion using the CIRCLE program in the VisuMax platform, and thin-flap LASIK have been recently established. While all options offer safety and efficacy comparable to LASIK retreatments, each has its patient-specific advantages and disadvantages. While surface ablation preserves the flap-free approach of the primary procedure, the aspect of pain and a slow visual recovery might render it less attractive as compared with CIRCLE and thin-flap LASIK which offer quick recovery, however at the price of flap creation. Besides, each retreatment method generates specific tissue responses and has a different impact on corneal biomechanics, which is strongly dependent on the previous SMILE parameters, especially the cap thickness.Conclusions:Refractive enhancement after SMILE is currently mostly performed by surface ablation, CIRCLE cap-to-flap conversion or thin-flap LASIK, which all offer safety and efficacy comparable to LASIK retreatments. In this review, a detailed overview over each method, its technical aspects, and specific advantages and disadvantages is given.

SmartSurfACE transepithelial photorefractive keratectomy with mitomycin C enhancement after small incision lenticule extraction

“…This technique requires accurate preoperative assessment, including epithelial thickness measurements by high-resolution anterior segment optical coherence tomography or very high-frequency ultrasound to prevent buttonholing. It also requires residual stroma calculations to avoid a gas breakthrough between the FS-LASIK and SMILE interface [ 29 ]. Furthermore, this would cause a disproportionate effect on corneal biomechanical strength [ 30 ].…”

Advances in refractive corneal lenticule extraction

“…However, the aspect of pain and a slow visual recovery might render it less appealing, particularly if it needs to be done bilaterally. [ 67 ] The SMILE cap can be converted into a FS-LASIK flap for secondary excimer laser application (CIRCLE). [ 68 ] Thin-flap LASIK, with a new flap anterior to the SMILE interface, can also be created.…”

“…Each enhancement method usually requires adjusted nomograms and generates specific tissue responses with a different impact on corneal biomechanics dependent on the previous SMILE parameters, especially the cap thickness. [ 67 69 ]…”

Research Progress on Morphological Changes and Surgery-Related Parameters of Corneal Cap in Small-Incision Lenticule Extraction

“…Reinstein et al [45] suggested that the prerequisite for successful secondary LASIK with a thin flap is the presence of at least 40 μm of space between the maximum epithelial thickness and the minimum cap thickness. Considering some postoperative reactions, such as epithelial thickening following the first SMILE operation [46], the initial cap thickness is designed to be ≥120 μm [47]. CIRCLE CIRCLE is achieved by changing the initial corneal cap into a corneal flap with femtosecond laser and then performing femtosecond-laser-assisted LASIK.…”