Meniscus-Shaped Stromal Lenticule Addition Keratoplasty for Corneal Regularization and Thickening in Advanced Keratoconus

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.

Cutting Edge: Corneal Stromal Lenticule Implantation (Corneal Stromal Augmentation) for Ectatic Disorders

ABSTRACT

The ectatic disease of the cornea poses a significant challenge for ophthalmologists because commonly used treatments to improve visual acuity, such as spectacles and contact lenses, may not be effective, especially in advanced stages. In addition, the preferred surgical management, corneal transplantation, has various issues related to tissue availability, the steep learning curve, and postoperative complications such as tissue stability and half-life. Ongoing research for an alternative to keratoplasty has suggested various methods, such as corneal crosslinking, which can improve visual function when combined with other techniques. Early reports have become available on the feasibility and safety of different strategies for corneal stromal augmentation, both with and without corneal crosslinking, and their favorable clinical outcomes, including visual and keratometry improvements. Here, we explore the cutting-edge advancements in stromal lenticule implantation, encompassing different facets of the procedure.

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.

Corneal Biomechanical Evaluation After Meniscus-Shaped Stromal Lenticule Addition Keratoplasty (MS-SLAK) for Keratoconus

PURPOSE

To evaluate corneal biomechanical changes after meniscus-shaped stromal lenticule addition keratoplasty (MS-SLAK) performed for the treatment of keratoconus.

METHODS

This interventional study included patients affected by advanced keratoconus (stage III and IV) who underwent examination with a dynamic Scheimpflug analyzer and non-contact tonometer (Corvis ST; Oculus Optikgeräte GmbH) at baseline and 12 months after MS-SLAK. The biomechanical parameters evaluated in this study were integrated inverse radius (1/R), deformation amplitude ratio (DA ratio), stiffness parameter at first applanation (SP-A1), biomechanical intraocular pressure (bIOP), central corneal thickness (CCT), and stress-strain index (SSI).

RESULTS

Sixteen patients were enrolled in the study. The analysis was ultimately conducted on 15 patients. Comparative analyses showed an increase in corneal stiffness as demonstrated by a rise in SSI (P < .0001) and SP-A1 (P < .0001) and a decrease in DA ratio (P < .0001) and 1/R (P = .01). A significant increase in CCT was found (P < .0001). No statistically significant modification was found for bIOP (P = .43).

CONCLUSIONS

The corneal biomechanical analyses evaluated by the Corvis ST showed that MS-SLAK for advanced keratoconus is able to increase corneal overall stiffness. This result is explained by the significant increase in thickness induced by MS-SLAK. [J Refract Surg. 2023;39(7):499-504.].

Customized Bowman-Stromal Inlay: An Attempt to Change the Topography of the Keratoconus Cornea

PURPOSE

The objective of this report is to describe a modification of a previously reported technique with an aim of improving the corneal topography and visual outcomes in progressive keratoconus along with stabilization of ectasia.

METHOD

In a 26-year-old man with progressive keratoconus, corneal collagen cross-linking was performed in one eye. The other eye had a keratometry of 69.6 D and thinnest pachymetry of 397 µm for which a customized Bowman-stromal inlay surgery was performed. The technique involved the harvesting of Bowman-stromal inlay (anterior 180-μm human donor cornea having the Bowman's layer and anterior stroma) using the femtosecond laser and central ablation of this inlay was done on the stromal side using an excimer laser. This customized inlay was placed in the anterior stromal pocket of the patient's cornea using a regular intraocular lens injector.

RESULTS

Stabilization of keratoconus could be achieved in the present case along with improvement in the corrected distance visual acuity and pachymetry. Maximum keratometry decreased from 69.6 D to 57.3 D.

CONCLUSIONS

Customized Bowman-stromal inlay technique appears to be a step towards creating an ideal inlay for the keratoconus cornea.