Is Crosslinked Corneal Donor Tissue Beneficial in PK?

Use of Donors Predisposed by Corneal Collagen Cross-linking in Penetrating Keratoplasty for Treating Patients With Keratoconus

Huang T, Ye R, Ouyang C, Hou C, Hu Y, Wu Q
Am J Ophthalmol. 2017;184:115-120

Background

Eyes with keratoconus undergoing corneal transplantation have among the highest success rates as far as graft clarity and longevity of all eyes undergoing keratoplasty. Many, if not most, patients with keratoconus have high expectations for good to excellent vision following their surgery.

One of the most frustrating outcomes of corneal transplantation for both patients and surgeons is a beautiful-looking, crystal-clear graft with poor vison due to refractive error, especially irregular astigmatism. This is not a new issue. There have been many modifications of the penetrating keratoplasty technique over the decades in an attempt to reduce refractive error and astigmatism (both regular and irregular) after corneal transplantation, whether it is penetrating keratoplasty or deep anterior lamellar keratoplasty (which is often done for eyes with keratoconus). While some techniques seem to help in the early postoperative period, the majority do not improve the refractive outcomes after all of the sutures are removed.

Study Summary

Huang and colleagues looked into whether the "strengthening" of the cornea that occurs with corneal crosslinking (a procedure most commonly performed for eyes with progressive keratoconus) might be beneficial in corneal donor tissue. They performed a fairly standard corneal crosslinking procedure on donor tissue and used it in a randomized fashion, comparing it with noncrosslinked donor tissue for penetrating keratoplasties in eyes with keratoconus. Both groups underwent the same penetrating keratoplasty technique and postoperative care. All sutures were removed by 18 months postoperatively in both groups.

Of note, they found slightly better uncorrected and best-corrected visual acuity in the crosslinked donor eyes than in the noncrosslinked donor eyes at 1 year postoperatively (with most or all sutures in), but both uncorrected and best-corrected visual acuity were statistically significantly better at 3 years postoperatively (with all sutures out for ≥ 18 months) in the crosslinked donor eye group. Manifest and keratometric cylinder were also statistically significantly better in the crosslinked donor eyes than in the noncrosslinked donor eyes at 3 years postoperatively. Additionally, simulated keratometry in the steepest meridian (Kmax) and corneal power were statistically significantly lower in the crosslinked donor eyes than in the noncrosslinked donor eyes at 3 years postoperatively.

From a safety standpoint, there was no difference in endothelial cell count, graft rejection episodes, and elevated intraocular pressure between the two groups.

Viewpoint

While 3 years may seem like a long-term study, it really is not that long in these eyes, as the expected longevity of penetrating keratoplasties for keratoconus is on the order of decades. We have longer-term data on corneal crosslinking for eyes with keratoconus, and there does not seem to be any great danger of endothelial decompensation over 5-10 years, but longer-term data are scarce. I am rather intrigued by the idea that an eye bank could crosslink the tissue without compromising the health of the endothelial cells and that this tissue might result in better visual results than standard non-crosslinked tissue.

While this study was on transplants in eyes with keratoconus, my guess is that the encouraging results might hold true for all penetrating keratoplasties.

One thing to keep in mind is that an epithelium-off crosslinking procedure was performed in these donor corneas. Consequently, a surgeon might not want to use this tissue in eyes where graft re-epithelialization might be problematic.

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