Risk Evaluation of Human Corneal Stromal Lenticules From SMILE for Reuse

Banking of post-SMILE stromal lenticules for additive keratoplasty: A new challenge for eye banks?

PURPOSE

ReLEx (Refractive Lenticule Extraction) Small Incision Lenticule Extraction (SMILE), the second generation of ReLEx Femtosecond Lenticule Extraction (FLEx), is a minimally invasive, flapless procedure designed to treat refractive errors such as myopia, hyperopia, presbyopia, and astigmatism. This review aims to provide a comprehensive overview of the methods for preserving SMILE-derived lenticules and discusses their potential future applications.

METHODS

A narrative literature review was conducted using PubMed, Scopus, and Web of Science databases, focusing on articles published up to January 2024 and available in English. The authors also evaluated the reference lists of the collected papers to identify any additional relevant research.

RESULTS

No standardized protocols currently exist for the storage or clinical application of SMILE-derived lenticules. However, these lenticules present a promising resource for therapeutic uses, particularly in addressing the shortage of donor corneal tissues. Their potential applications include inlay and overlay additive keratoplasty, as well as other ocular surface applications. Further research is needed to establish reliable protocols for their preservation and clinical use.

CONCLUSION

SMILE-derived lenticules offer significant potential as an alternative to donor corneal tissues. Standardizing their storage and application methods could enhance their use in clinical settings.

Impact of Latent Virus Infection in the Cornea on Corneal Healing after Small Incision Lenticule Extraction

The aim of the present study is to analyze the impact of cornea virus latent infection on corneal healing after small incision lenticule extraction (SMILE) and predict the positive rate of virus latent infection in corneal stroma. A total of 279 patients who underwent SMILE were included in this study. Fluorescence quantitative PCR was used to detect virus infection in the lenticules, which were taken from the corneal stroma during SMILE. Herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), Epstein-Barr virus (EBV), and cytomegalovirus (CMV) were detected. Postoperative visual acuity, spherical equivalent, intraocular pressure, corneal curvature (Kf and Ks), corneal transparency, and corneal staining were compared between the virus-positive group and the virus-negative group. The number of corneal stromal cells and inflammatory cells, corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), corneal total branch density (CTBD), and corneal nerve fiber width (CNFW) were evaluated using an in vivo confocal microscope. Out of 240 herpes simplex virus (HSV) tested samples, 11 (4.58%) were positive, among which 5 (2.08%) were HSV-1-positive and 6 (2.50%) were HSV-2-positive. None of the 91 CMV- and EBV-tested samples were positive. There was no statistical significance in the postoperative visual acuity, spherical equivalent, intraocular pressure, Kf and Ks, corneal transparency, corneal staining, the number of corneal stromal cells and inflammatory cells, CNFD, CNBD, CNFL, CTBD, and CNFW between the virus-positive and virus-negative groups (p > 0.05). In conclusion, there is a certain proportion of latent HSV infection in the myopia population. Femtosecond lasers are less likely to activate a latent infection of HSV in the cornea. The latent infection of HSV has no significant impact on corneal healing after SMILE.

An Efficient Technique for the Long-term Preservation of SMILE Lenticules Using Desiccation

PURPOSE

To evaluate a desiccation protocol for the long-term preservation of human small incision lenticule extraction (SMILE) lenticules and to study their integration in an in vivo rabbit model.

METHODS

Lenticules were retrieved after SMILE procedures in patients, then desiccated according to a novel protocol. Histologic and electron microscopic analyses were performed. Six rabbit eyes received grafts with an inlay technique, which consisted of inserting a desiccated lenticule into a stromal pocket. Rabbits were killed at different times between 6 and 24 weeks. Rabbit corneas were analyzed using optical coherence tomography, histology, and DAPI staining.

RESULTS

Microscopic analysis of desiccated lenticules showed a preserved stromal architecture after rehydration. A decellularization of the lenticules after desiccation was observed without any chemical treatment. All rabbit corneas remained clear after grafting human lenticules and no rejection occurred. Optical coherence tomography showed regular lenticular implantation and no decrease in lenticule thickness. Histologic analysis showed no inflammatory infiltration around lenticules and no nuclear material inside lenticules after 6 months.

CONCLUSIONS

A favorable integration of desiccated human SMILE lenticules in rabbit corneas was observed. The refractive issue of lenticular implantation must be investigated next. Clinical trials are needed to evaluate the use of desiccated SMILE lenticules to treat hyperopia or keratoconus in humans. [J Refract Surg. 2023;39(7):491-498.].

Update of Research Progress on Small Incision Lenticule Extraction (SMILE) Lenticule Reuse

The SMILE lenticule is a complete corneal stroma that is removed from SMILE surgery. Since the increasing number of SMILE surgeries, a large number of SMILE lenticules have been produced, so the reuse and preservation of the stromal lens has become a research hotspot. Due to the rapid development of the preservation and clinical reuse of SMILE lenticules, there have been many related studies in recent years, so we updated it on this basis. We searched PubMed, Web of Science, Embase, Elsevier Science, CNKI, WANFANG Data and other databases for all articles published on the preservation and clinical reuse of SMILE lenticules, screened useful articles, selected relevant articles published in the last five years as the main body for summary, and then reached a conclusion. The existing preservation methods of SMILE lenticule include Moist chamber storage at low temperature, cryopreservation technique dehydrating agent and corneal storage medium, which have their own advantages and disadvantages. Presently, smile lenticules can be used for the treatment of corneal ulcers and perforations, corneal tissue defects, hyperopia, presbyopia and keratectasia, which have been proven to be relatively effective and safe. More research on smile lenticule reuse needs to be carried out to confirm its long-term efficacy.

Norepinephrine as an Enhancer Promoting Corneal Penetration of Riboflavin for Transepithelial Corneal Crosslinking

Purpose

Previously, we found norepinephrine (NE) could affect the corneal epithelial integrity, herein we investigated the feasibility and safety of NE serving as a chemical enhancer to promote corneal penetration of riboflavin during transepithelial corneal crosslinking (CXL).

Methods

The dosage of NE that could promote riboflavin diffusion through the healthy epithelial barrier without inducing epithelial damage in C57BL/6 mice was determined. The safety of NE treatment was confirmed by morphological and histological examinations of the whole cornea. The efficacy of NE in promoting riboflavin penetration was verified by slit lamp and scanning electron microscope (SEM), and corneal biomechanical measurement after CXL. To better fit the clinical scenario, increased NE dosage and shortened riboflavin infiltration time were further evaluated.

Results

The lowest dosage of NE (1 mg/mL) that facilitated transepithelial riboflavin permeation was 2 µL. No visible corneal structure alteration was observed after NE treatment. SEM indicated dissociation of intercellular junctions among corneal epithelial cells. Homogenous distribution of riboflavin throughout corneal stroma was observed. NE-treated corneas reached comparable biomechanical properties after CXL, including stress-relaxation curve and elastic modulus, with corneas treated with the commercially available transepithelial drug Peschke TE. To better fit the clinical scenario, increasing NE up to 5.5 µL helped riboflavin infiltrate the corneal stroma within 30 minutes. After CXL with 9 mW/cm2 ultraviolet-A (UVA) for 2.5 minutes, the cornea showed significantly enhanced corneal biomechanical properties with undisturbed corneal endothelium.

Conclusions

NE serves as an effective enhancer in increasing riboflavin diffusion with limited impairment on corneal epithelium and has great potential for clinical application.

Translation Relevance

NE serves as an effective enhancer for riboflavin penetration and clinical transepithelial CXL.

Experiment-Based Validation of Corneal Lenticule Banking in a Health Authority-Licensed Facility

With the expected rise in patients undergoing refractive lenticule extraction worldwide, the number of discarded corneal stromal lenticules will increase. Therefore, establishing a lenticule bank to collect, catalog, process, cryopreserve, and distribute the lenticules (for future therapeutic needs) could be advantageous. In this study, we validated the safety of lenticule banking that involved the collection of human lenticules from our eye clinic, transportation of the lenticules to a Singapore Ministry of Health-licensed lenticule bank, processing, and cryopreservation of the lenticules, which, after 3 months or, a longer term, 12 months, were retrieved and transported to our laboratory for implantation in rabbit corneas. The lenticule collection was approved by the SingHealth Centralised Institutional Review Board (CIRB). Both short-term and long-term cryopreserved lenticules, although not as transparent as fresh lenticules due to an altered collagen fibrillar packing, did not show any sign of rejection and cytotoxicity, and did not induce haze or neovascularization for 16 weeks even when antibiotic and steroidal administration were withdrawn after 8 weeks. The lenticular transparency progressively improved and was mostly clear after 4 weeks, the same period when we observed the stabilization of corneal hydration. We showed that the equalization of the collagen fibrillar packing of the lenticules with that of the host corneal stroma contributed to the lenticular haze clearance. Most importantly, no active wound healing and inflammatory reactions were seen after 16 weeks. Our study suggests that long-term lenticule banking is a feasible approach for the storage of stromal lenticules after refractive surgery.