Fresh Human Myopic Lenticule Intrastromal Implantation for Keratoconus Using SMILE Surgery in a Long-term Follow-up Study: Ultrastructural Analysis by Transmission Electron Microscopy

SMILE-Derived Corneal Stromal Lenticule: Experimental Study as a Corneal Repair Material and Drug Carrier

PURPOSE

A detailed study of the physicochemical properties of SMILE-derived lenticules and evaluation of their drug delivery after loading with silver nanoparticles (AgNPs).

METHODS

The lenticules were decellularized and modified with crosslinking concentrations of 0.01 (0.01E/L), 0.05 (0.05E/L), and 0.25 (0.25E/L) mmol N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) per mg lenticule at 5:1 carbodiimide/N-hydroxysuccinimide (EDC/NHS) ratios. The degree of swelling, light transmittance, biomechanical properties, and stability of the non-crosslinked decellularized lenticules (DLs), 0.01E/L, 0.05E/L, and 0.25E/L were measured and characterized using Fourier transform infrared spectroscopy and transmission electron microscopy with non-crosslinked non-decellularized lenticules as controls. DLs, 0.01E/L, 0.05E/L, and 0.25E/L were soaked in AgNPs for 24 hours, and the concentration of the drug released was measured.

RESULTS

There was no significant difference in the degree of swelling between the groups (P > 0.05). The light transmittance of the lenticules did not change after decellularization and crosslinking and decreased after loading with AgNPs. Non-decellularized lenticules biodegraded within 108 to 120 hours, and the other groups biodegraded within 96 to 108 hours in vitro. The 0.01E/L had the highest tensile strength. The absorption peak intensity ratio of the amide I band and the amide II band decreased, and the arrangement of collagen fibers was more compact in crosslinked decellularized lenticules. The 0.01E/L had the highest cumulative drug release (3.4 ± 0.91 μg).

CONCLUSIONS

Crosslinking decellularization improved the biomechanical properties and resistance to water absorption of lenticules, increased covalent bonds between collagen fibers, and improved drug delivery. Crosslinked decellularized lenticules can be used as a new corneal patch material and drug delivery carrier for drug AgNPs.

Low-temperature vacuum evaporation as a novel dehydration process for the long-term preservation of transplantable human corneal tissue

Globally there is a shortage of available donor corneas with only 1 cornea available for every 70 needed. A large limitation to corneal transplant surgery is access to quality donor tissue due to inadequate eye donation services and infrastructure in many countries, compounded by the fact that there are few available long-term storage solutions for effectively preserving spare donor corneas collected in countries with a surplus. In this study, we describe a novel technology termed low-temperature vacuum evaporation (LTVE) that can effectively dry-preserve surplus donor corneal tissue, allowing it to be stored for approximately 5 years, shipped at room temperature, and stored on hospital shelves before rehydration prior to ophthalmic surgery. The dry-preserved corneas demonstrate equivalent biological characteristics to non-dried donor tissue, with the exception that epithelial and endothelial cells are removed and keratocytes are rendered non-viable and encapsulated within the preserved extracellular matrix. Structure and composition of the dried and rehydrated corneas remained identical to that of non-dried control corneas. Matrix-bound cytokines and growth factors were not affected by the drying and rehydration of the corneas. The ability to preserve human donor corneas using LTVE will have considerable impact on global corneal supply; utilisation of preserved corneas in lamellar keratoplasties, corneal perforations, ulcers, and tectonic support, will allow non-preserved donor tissue to be reserved for where it is truly required.

Long-term results of allogenic corneal lenticule of hyperopic SMILE for post-LASIK ectasia

Post-laser-assisted in situ keratomileusis (LASIK) corneal ectasia is a severe complication of corneal refractive surgery, and cryopreserved lenticules from hyperopic small incision lenticule extraction (SMILE) may offer a promising treatment though their long-term safety and efficacy are still under investigation. In this prospective case series, six eyes from six patients with post-LASIK ectasia received lenticules (mean cryopreserved time: 63 days). The procedure involved lifting the corneal flap, implanting the lenticule, and repositioning the flap. Over a follow-up period of at least one year, uncorrected distance visual acuity (UDVA) improved from 1.52 ± 0.40 preoperatively to 0.74 ± 0.28 LogMAR. Two eyes gained one line of corrected distance visual acuity (CDVA), three gained two lines, and one gained over three lines. Spherical equivalents decreased from -14.67 ± 2.36 D to -8.75 ± 4.03 D (p = 0.02). Mean anterior K and total corneal refractive power decreased (p < 0.05). Thinnest corneal thickness increased from 359.2 ± 39.3 μm to 401.7 ± 53.4 μm (p = 0.02). These findings support the potential of cryopreserved lenticules for treating post-LASIK ectasia, though further refinement in refractive predictability is needed.

Histochemical and ultrastructural evaluation of myopic corneal lenticules based on refractive error

BACKGROUND

This study aimed to investigate cell degeneration, apoptosis, and ultrastructural differences in refractive lenticules (RL) obtained using small incision lenticule extraction (SMILE) compared with spherical equivalence (SE) refraction values.

METHODS

This study included 84 eyes from 42 patients. Patients were divided into two groups according to the SE values: those with values below 4 diopters (D) (Group 1) and above 4 diopters (D) (Group 2). Patients who did not belong to the same SE group were excluded from the study. One RL obtained from each patient was separated for light microscopy and immunohistochemical examinations, and another for transmission electron microscopy (TEM) examinations. Caspase-3 for apoptosis and alpha-smooth muscle actin (α-SMA) for cell degeneration were evaluated using immunohistochemical examinations.

RESULTS

Histological analyses showed that the density of collagen fibres was greater in Group 1 than in Group 2. Glycoaminoglycan and glycoprotein staining intensities were also higher in Group 1. TEM observations showed that Group 1 had intact cell and nuclear membranes, peripheral heterochromatin, and large nuclei, while Group 2 showed heterochromatin condensation and fragmentation, increased intracellular vacuoles, and loss of cytoplasm. Immunohistochemical analyses revealed that α-SMA and caspase-3 were significantly higher in Group 2 than in Group 1 (p < 0.001 and p < 0.001, respectively).

CONCLUSIONS

Cell degeneration and apoptosis were significantly more common in the RLs with high SE values after SMILE surgery. The tissue response induced by surgery was more severe in the RLs with high SE values. This should be considered when reusing RLs.

Ocular Surface Fluid: More than a Matrix

Although the eye can be subjected to therapeutic manipulation, some of its structures are highly inaccessible. Thus, conventional therapeutic administration pathways, such as topical or systemic routes, usually show significant limitations in the form of low ocular penetration or the appearance of side effects linked to physiology, among others. The critical feature of many xenobiotics is the drug gradient from the concentrated tear reservoir to the relatively barren corneal and conjunctival epithelia, which forces a passive route of absorption. The same is true in the opposite direction, towards the ocular surface (OS). With the premise that tears can be regarded as equivalent to or a substitute for plasma, researchers may determine drug concentrations in the OS fluid. Within this framework, a survey of scholarly sources on the topic was conducted. It provided an overview of current knowledge, allowing the identification of relevant theories, methods, and gaps in the existing research that can be employed in subsequent research. OS fluid (tears particularly) has enormous potential as a source of biological material for external drug screening and as a biomarker of various systemic diseases. Given the numerous alternate matrices, knowledge of their properties is very important in selecting the most appropriate specimens in toxicological analyses.

Update on corneal crosslinking for keratoconus and corneal ectasia

PURPOSE OF REVIEW

To review corneal crosslinking for keratoconus and corneal ectasia, and recent developments in the field. This study will review the mechanism of crosslinking, clinical approaches, current results, and potential future innovations.

RECENT FINDINGS

Corneal crosslinking for keratoconus was first approved by U.S. FDA in 2016. Recent studies have confirmed the general long-term efficacy of the procedure in decreasing progression of keratoconus and corneal ectasia. New types of crosslinking protocols, such as transepithelial treatments, are under investigation. In addition, adjunctive procedures have been developed to improve corneal contour and visual function in these patients.

SUMMARY

Crosslinking has been found to be well tolerated and effective with the goal of decreasing progression of ectatic corneal diseases, keratoconus and corneal ectasia after refractive surgery. Studies have shown its long-term efficacy. New techniques of crosslinking and adjunctive procedures may further improve treatments and results.

Lenticule addition keratoplasty for the treatment of keratoconus: A systematic review and critical considerations

Keratoconus is a corneal disorder characterized by the progressive thinning and bulging of the cornea. Currently, the major goal of management is to halt its progression, restore normal corneal strength, prevent acute complications, and save vision. Penetrating keratoplasty and deep anterior lamellar keratoplasty as conventional surgical methods for advanced keratoconus are limited by relatively high rates of immune intolerance, slow post-operational recovery, high costs, and shortage of donor corneas. Recently, the development of lenticule addition keratoplasty enables the restoration of corneal thickness simply by implanting a lenticule into the stromal pocket created with the femtosecond laser, which can originate from cadaver corneas or more appealing, be extracted from patients via a small-incision lenticule extraction (SMILE) surgery. As the first systematic review in this field, we critically review publications on lenticule addition keratoplasty and provide our perspectives on its clinical application and the focus of future research.