Reshaping and Customization of SMILE-Derived Biological Lenticules for Intrastromal Implantation

Purpose

To evaluate the feasibility of excimer laser reshaping of biological lenticules available after small incision lenticule extraction (SMILE).

Methods

Fresh and cryopreserved SMILE-derived human lenticules underwent excimer laser ablation for stromal reshaping. The treatment effects in the lasered group were compared with the nonlasered group with respect to changes in surface functional groups (by Fourier transform infrared spectroscopy [FTIR]) and surface morphology (by scanning electron microscopy [SEM] and atomic force microscopy [AFM]). Ten SMILE-derived porcine lenticules, five nonlasered (107-μm thick, -6 diopter [D] spherical power) and five excimer lasered (50% thickness reduction), were implanted into a 120-μm stromal pocket of 10 porcine eyes. Corneal thickness and topography were assessed before and after implantation.

Results

FTIR illustrated prominent changes in the lipid profile. The collagen structure was also affected by the laser treatment but to a lesser extent. SEM exhibited a more regular surface for the lasered lenticules, confirmed by the lower mean Rz value (290.1 ± 96.1 nm vs. 380.9 ± 92.6 nm, P = 0.045) on AFM. The lasered porcine lenticules were thinner than the nonlasered controls during overhydration (132 ± 26 μm vs. 233 ± 23 μm, P < 0.001) and after 5 hours in a moist chamber (46 ± 3 μm vs. 57 ± 3 μm, P < 0.001). After implantation, the nonlasered group showed a tendency toward a greater increase in axial keratometry (6.63 ± 2.17 D vs. 5.60 ± 3.79 D, P = 0.613) and elevation (18.6 ± 15.4 vs. 15.2 ± 5.5, P = 0.656) than the lasered group.

Conclusions

Excimer laser ablation may be feasible for thinning and reshaping of SMILE-derived lenticules before reimplantation or allogenic transplantation. However, controlled lenticule dehydration before ablation is necessary in order to allow stromal thinning.

LASIK and surface ablation in corneal dystrophies

Corneal dystrophies are a rare group of hereditary disorders, that are bilateral, non-inflammatory, and progressive. Clinically, they can be classified based on the anatomic layer of the cornea affected. Refractive surgery and phototherapeutic keratectomy (PTK) can be performed with caution in patients with certain corneal dystrophies, but should be avoided in others. For epithelial basement membrane dystrophy, photorefractive keratectomy (PRK) is the procedure of choice for treatment of refractive error, and PTK may be performed for the treatment of recurrent erosions or irregular astigmatism. PRK and laser-assisted in situ keratomileusis (LASIK) have been associated with exacerbation of combined granular-lattice corneal dystrophy. LASIK and PRK appear to be safe in mild forms of posterior polymorphous corneal dystrophy, whereas LASIK should be avoided in Fuchs dystrophy. The safety of refractive surgery and PTK in the remainder of epithelial, Bowman layer, and stromal dystrophies has yet to be established.