Femtosecond laser assisted peripheral stromal keratoplasty effective for corneal ectasia: Study
Keratoconus (KCN) and pellucid marginal degeneration (PMD) are bilateral, asymmetrical, noninflammatory, and progressive ectatic corneal conditions, characterized by stromal thinning leading to distortion of the corneal surface. In severe cases with irregular astigmatism where contact lenses cannot be used, or when corneal stromal opacity is present, lamellar or penetrating keratoplasty is the mainstay of treatment. Due to the costs and complications of corneal transplantation, research is ongoing to delay or replace it with simpler methods, such as intracornealring segments (ICRSs).
Although long‑term studies have shown the effectiveness of these implants in delaying corneal transplantation; melting of corneal stroma over the polymethyl methacrylate (PMMA) implants, migration of synthetic rings to the incision site, and corneal ulcers are major concerns. These complications are not uncommon, both when the ring is manually inserted into the cornea or when the procedure is femtosecond laser‑assisted.
The study by Jafarinasab M, Hadi Y. aimed to investigate the visual outcomes and complications of implanting differently shaped allogeneic corneal segments in the peripheral stroma of ectatic corneas.
This prospective, noncomparative case series included patients with primary corneal ectasia including keratoconus and pellucid marginal degeneration. In the operating room, one or two ring or crescent‑shaped allogeneic corneal segments were prepared using a handmade double‑bladed punch, which were then implanted by a specially designed device, into stromal channels in the peripheral recipient cornea fashioned with a femtosecond‑laser system.
A total of 15 eyes of 13 patients with mean age of 31.73 years were operated. There were significant improvements in uncorrected (0.68 to 0.3 logMAR) and corrected (0.44 to 0.16 logMAR) visual acuity, mean sphere, mean spherical equivalent refractive error, and mean keratometry (steep, flat, and average). Topographic and refractive astigmatism did not change significantly. Complications included a single case of bacterial keratitis secondary to epithelial defect, which was controlled with topical antibiotics eventually leading to an uncorrected vision of 20/25 one year after surgery.
Various interventions have been designed to delay or replace corneal transplantation in patients with KCN or PMD. ICRSs were designed to flatten central corneal curvature and achieve refractive improvement leaving the optical center of the cornea intact.
In this study, using the remaining anterior corneal button of DSAEK donor tissues, authors prepared allogeneic corneal ring segments and placed them in channels created in the patient's ectatic cornea using a femtosecond laser. The results showed a significant improvement in UDVA, SCDVA, spherical equivalent, and flat, steep, and average K‑readings in the central 3‑mm zone. In addition to becoming flat, corneal topography became more regular.
Since in patients with corneal ectasia, unlike those with usual refractive errors, the primary goal of surgical intervention is not to obtain spectacle independence, but to restore vision with the help of glasses that are tolerable; in this study, the criterion for effectiveness of the procedure was the improvement in SCDVA.
Biological rings increase corneal thickness at the location of implantation and since they are soft and malleable, concerns are reduced regarding its displacement inside the cornea or damage to adjacent tissues such as Descemet's membrane. This may imply their ability for use corneas of various thicknesses, however, further studies are needed to ascertain this. None of the patients reported symptoms such as glare or halo, which are not uncommon with synthetic ICRSs. This could be because the refractive index of allogeneic segments is the same as that of the recipient cornea, and that the implants are not rigid and unlike synthetic types they have no sharp edge.
Since authors used DSAEK buttons, in the absence of endothelium and epithelium, which are known to be more antigenic, one does not expect other types of corneal graft rejection. Processing of the transplanted corneal tissue with gamma irradiation may further diminish the allogenicity of donor corneal material. Biological rings or segments may be procured from remnants of donor corneas already used for lamellar or penetrating keratoplasty, anterior corneal buttons leftoverfrom DSAEK surgery, or even corneal donors unsuitable for optical keratoplasty. Such recycling of donor material residues or corneal tissues that do not meet transplantation requirements can help significantly reduce treatment costs.
"In summary, based on the preliminary results of our study, employing intrastromal corneal allogeneic ring segments for KCN and PMD may be an effective, low‑risk, simple, and economic option. Further studies should be conducted employing larger sample size, longer follow‑up, and more accurate instruments for better evaluation of this new method."
Source: Jafarinasab M, Hadi Y. Femtosecond laser-assisted peripheral additive stromal keratoplasty for treatment of primary corneal ectasia: Preliminary outcomes. Indian J Ophthalmol 2021;69:2663-8.
DOI: 10.4103/ijo.IJO_3206_20
