Long-Term Dehydrated Donor Lamella Survival in Anterior Keratoplasty: Keratocyte Migration and Repopulation of Corneal Stroma

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.].

Ultrastructural Analysis of Rehydrated Human Donor Corneas After Air-Drying and Dissection by Femtosecond Laser

Purpose: To evaluate the efficiency of femtosecond laser (FSL) incision of rehydrated human donor corneas after air-drying and its effects on corneal structure.

Methods: We compared the rehydrated and fresh-preserved corneas by microscopy following Victus-Tecnolas FSL treatment for straight-edge anterior lamellar keratoplasty (ALK). The corneas were dehydrated at room temperature under a laminar-flow hood.

Results: To obtain the horizontal cut in rehydrated corneas, we increased the FSL pulse energy to 1.2 μJ from 0.80 μJ applied for the fresh corneas and obtained a clear-cut separation of the lamellar lenticule cap from the corneal bed. Light microscopy showed regular arrangement of stromal collagen lamellae, with spaces in between the fibers in the corneal stroma in the fresh and the rehydrated corneas, but the uppermost epithelial layers in the rehydrated corneas were lost. Transmission electron microscopy (TEM) revealed no signs of thermal or mechanical damage to the corneal structure. The epithelial basal membrane and Bowman's layer maintained their integrity. The epithelial basal layer and cells were separated by large spaces due to junction alteration in the rehydrated corneas. There were gaps between the lamellar layers in the stroma, especially in the rehydrated corneas. Keratocytes displayed normal structure in the fresh corneas but were devoid of microorganules in the rehydrated corneas. Minor irregularities were observed in the vertical incision and the horizontal stroma appeared smooth on scanning electron microscopy.

Conclusion: The corneal stroma of rehydrated corneas maintained morphology and integrity, while corneal cellular components were generally altered. When corneas are intended for FSL-assisted ALK, effective stromal bed incision is best achieved at a laser power higher than that currently adopted for fresh corneas.

Biobanking of Dehydrated Human Donor Corneal Stroma to Increase the Supply of Anterior Lamellar Grafts

PURPOSE

To investigate the effect of dehydration on human donor corneal stroma for biobanking.

METHODS

Epithelium and endothelium of research-grade human donor corneas (n = 12) were scraped off, leaving a bare stroma with attached sclera. The tissues were placed in a large Petri dish prefilled with silica gel in the periphery and stored at room temperature for 14 days. At the end of preservation, the tissues were rehydrated by being submerged in phosphate-buffered saline for 15 minutes. Transparency (using a custom-built device) and thickness (using optical coherence tomography) measurements were recorded before dehydration, after dehydration, and after rehydration of the tissues. Periodic acid-Schiff and alpha-smooth muscle actin (α-SMA) staining before dehydration and after rehydration were performed to determine the presence of keratocytes and expression of α-SMA. Tensile stress-strain before dehydration and after rehydration was performed to evaluate the biomechanical properties.

RESULTS

No difference in corneal transparency before dehydration (69.57 ± 6.41%) and after rehydration (67.37 ± 2.82%), P = 0.36, was observed. The corneas were more compact after dehydration. A significant change in thickness between before dehydration (625.8 ± 75.58 μm) and after rehydration (563.6 ± 15.77 μm) stage, P = 0.03, was noticed. The thickness was reduced to 147.6 ± 3.71 μm when dehydrated. Periodic acid-Schiff staining showed presence of stromal keratocytes and α-SMA protein expressed in control, dehydrated, and rehydrated corneas. There was no significant difference in the stiffness between control (27.86 ± 11.65 MPa) and rehydrated corneas (31.46 ± 11.41 MPa).

CONCLUSIONS

Human donor corneal stroma can be biobanked for up to 2 weeks in a dehydrated condition without losing their molecular or biomechanical properties after rehydration.