Electron Beam Irradiated Corneal Versus Gamma-Irradiated Scleral Patch Graft Erosion Rates in Glaucoma Drainage Device Surgery

Long-Term Results of Sterile Corneal Allograft Ring Segments Implantation in Keratoconus Treatment

PURPOSE

To evaluate the efficacy and safety of sterile corneal allograft ring segments implantation for the treatment of keratoconus by analyzing long-term visual, refractive, and tomographic clinical outcomes.

METHODS

This prospective study included 62 eyes of 49 patients with keratoconus who underwent corneal allograft ring segments implantation at Istanbul Medipol University Faculty of Medicine between February 2020 and August 2022. Surgical outcomes using the Istanbul nomogram were evaluated in patients preoperatively and postoperatively at 1 month, 6 months, 1 year, and 3 years. Outcomes measured were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), spherical refraction (SR), cylindrical refraction (CR), topographic keratometric values, and corneal thickness at the thinnest point.

RESULTS

Preoperative mean UDVA and CDVA (LogMAR) were 0.96 ± 0.50 and 0.72 ± 0.47, respectively, and increased to 0.41 ± 0.34 and 0.22 ± 0.19 at the last visit (P < 0.001). There was a significant decrease in SE, SR, and keratometric values postoperatively (P < 0.001). There was no difference in CR and thinnest corneal thickness values (P = 0.333 and 0.154, respectively). The stromal and epithelial thicknesses measured by anterior segment optical coherence tomography were stabilized at 6 months and 1 year, respectively. No major complications or side effects were observed intraoperatively or postoperatively.

CONCLUSIONS

This study demonstrated that sterile corneal allograft ring segments implantation is a safe and feasible treatment for keratoconus, yielding notable long-term visual outcomes with minimal implant-related complications.

Electron beam-irradiated donor cornea for on-demand lenticule implantation to treat corneal diseases and refractive error

The cornea is the major contributor to the refractive power of the eye, and corneal diseases are a leading cause of reversible blindness. The main treatment for advanced corneal disease is keratoplasty: allograft transplantation of the cornea. Examples include lenticule implantation to treat corneal disorders (e.g. keratoconus) or correct refractive errors. These procedures are limited by the shelf-life of the corneal tissue, which must be discarded within 2-4 weeks. Electron-beam irradiation is an emerging sterilisation technique, which extends this shelf life to 2 years. Here, we produced lenticules from fresh and electron-beam (E-beam) irradiated corneas to establish a new source of tissue for lenticule implantation. In vitro, in vivo, and ex vivo experiments were conducted to compare fresh and E-beam-irradiated lenticules. Results were similar in terms of cutting accuracy, ultrastructure, optical transparency, ease of extraction and transplantation, resilience to mechanical handling, biocompatibility, and post-transplant wound healing process. Two main differences were noted. First, ∼59% reduction of glycosaminoglycans resulted in greater compression of E-beam-irradiated lenticules post-transplant, likely due to reduced corneal hydration-this appeared to affect keratometry after implantation. Cutting a thicker lenticule would be required to ameliorate the difference in refraction. Second, E-beam-sterilised lenticules exhibited lower Young's modulus which may indicate greater care with handling, although no damage or perforation was caused in our procedures. In summary, E-beam-irradiated corneas are a viable source of tissue for stromal lenticules, and may facilitate on-demand lenticule implantation to treat a wide range of corneal diseases. Our study suggested that its applications in human patients are warranted. STATEMENT OF SIGNIFICANCE: Corneal blindness affects over six million patients worldwide. For patients requiring corneal transplantation, current cadaver-based procedures are limited by the short shelf-life of donor tissue. Electron-beam (E-beam) sterilisation extends this shelf-life from weeks to years but there are few published studies of its use. We demonstrated that E-beam-irradiated corneas are a viable source of lenticules for implantation. We conducted in vitro, in vivo, and ex vivo comparisons of E-beam and fresh corneal lenticules. The only differences exhibited by E-beam-treated lenticules were reduced expression of glycosaminoglycans, resulting in greater tissue compression and lower refraction suggesting that a thicker cut is required to achieve the same optical and refractive outcome; and lower Young's modulus indicating extra care with handling.

Microstructure characteristics of cornea of some birds: a comparative study

Background

Light is the critical factor that affects the eye's morphology and auxiliary plans. The ecomorphological engineering of the cornea aids the physiological activities of the cornea during connections between photoreceptor neurons and light photons. Cornea was dissected free from the orbit from three avian species as ibis (Eudocium albus), duck (Anas platyrhynchus domesticus) and hawk (Buteo Buteo) and prepared for light and scanning electron microscopy and special stain for structural comparison related to function.

Results

The three investigated avian species are composed of three identical layers; epithelium, stroma, and endothelium, and two basement membranes; bowman's and Descemet’s membrane, separating two cellular layers, except for B. buteo which only has a Descemet’s membrane. The corneal layers in the investigated species display different affinity to stain with Periodic Acid Schiff stain. The external corneal surface secured by different normal epithelial cells ran from hexagonal to regular polygonal cells. Those epithelial cells are punctured by different diameter microholes and microplicae and microvilli of various length. Blebs are scarcely distributed over their surface. The present investigation utilized histological, histochemical and SEM examination.

Conclusions

The study presents a brief image/account of certain structures of cornea for three of Avian’s species. Data distinguish the anatomic structures of the owl's eye. The discussion explains the role of some functional anatomical structures all through the vision.

Preserved corneal lamellar transplantation for infectious and noninfectious scleral defects: Three case reports and literature review

RATIONALE

: Reinforcement of thinned or necrotizing sclera has been conducted using various materials, including allogeneic sclera, allogenic cornea, amniotic membrane, fascia lata, pericardium, periosteum, and perichondrium. Among them, good outcomes have traditionally been obtained using preserved scleral grafts. However, scleral patch grafts have complications such as graft retraction, thinning, dehiscence, and necrosis. Furthermore, to promote epithelial healing, scleral patch grafting must be accompanied by procedures such as amniotic membrane transplantation (AMT) or grafting using conjunctival flaps or autografts. Recently, acellular preserved human corneas have been used in various ophthalmic surgeries, with emerging evidence supporting its use for treating scleral defects as an option that does not require AMT or conjunctival autografting. We investigated whether corneal patch grafting would show wound healing and tectonic success rate outcomes comparable to those of existing techniques.

PATIENT PRESENTATION

: Three patients presented with intractable ocular pain. Slit-lamp examination showed marked scleral thinning at the nasal side.

DIAGNOSIS

: Scleral thinning progressed with conservative treatment; microbial staining and culturing were performed. Infectious or non-infectious scleritis was diagnosed according to slit-lamp examination and microbial culture results.

INTERVENTIONS

: A preserved corneal lamellar patch was grafted at the scleral thinning area.

OUTCOMES

All patients achieved tectonic success with reduction of inflammation following corneal patch grafting. Two patients achieved complete re-epithelialization within 7 days, while 25 days were required for the third patient. No patients experienced graft thinning, rejection, or infection.

LESSONS

: Our report suggests the feasibility of using acellular preserved human cornea patch grafts to reinforce inflammatory scleral defects and obtain successful outcomes in terms of wound healing. This technique shows a comparable tectonic success rate and superior effect on scleral defect healing without the need for adjunctive AMT or conjunctival autografting.

Preserved Corneal Lamellar Grafting Reduces Inflammation and Promotes Wound Healing in a Scleral Defect Rabbit Model

Purpose

To investigate the effect of preserved corneal lamellar grafting on inflammation and wound healing and to compare its effect with that of preserved scleral grafting in a scleral defect rabbit model.

Methods

New Zealand White rabbits were assigned to a corneal lamellar grafting group (n = 5) or a scleral grafting group (n = 5). After lamellar dissection of superotemporal sclera using 6.0-mm trephine, the same sizes of preserved human corneal or scleral grafts were transplanted with 10-0 nylon interrupted sutures. The grafted areas were photodocumented at 3 to 21 days after surgery to evaluate epithelial wound healing index (%), neovascularization and presence of filaments. The existence of CD3⁺ T cells and CD34⁺ cells at the grafted areas was analyzed at 21 days.

Results

Epithelial wound healing index was significantly higher in the corneal grafting group at 9 days (P < 0.05). Scleral grafts showed copious formation of filaments adherent to the engrafted area from 9 to 14 days, whereas the corneal grafts were free of filaments. The numbers of inflammatory cells were significantly higher in the scleral grafts (P < 0.05), and CD3⁺ T cells and CD34⁺ cells were populated within inflammatory cells at graft-recipient junctions in both groups. The mean areas of the estimated perigraft and intragraft neovascularization tended to be higher in scleral grafts.

Conclusions

Preserved corneal lamellar grafting enhances epithelial wound healing and alleviates inflammation in a scleral defect rabbit model.

Translational Relevance

This work suggests that the preserved corneal graft may be considered as a favorable alternative option for repairing scleral defects.