Corneal Transplantation After Refractive Surgery
Corneal transplantation is occasionally required after refractive surgery. Reasons for needing a corneal graft after refractive surgery include significant corneal scarring, irregular astigmatism, corneal ectasia, and corneal edema. Issues unrelated to refractive surgery, such as trauma, infectious keratitis, or corneal edema after cataract surgery, can also necessitate corneal transplant surgery. Each type of refractive surgical procedure is unique in the reasons a graft may be required and in ways to avoid problems with the corneal transplant. Corneal transplantation techniques and indications are discussed in greater detail in BCSC Section 8, External Disease and Cornea.
After RK, a graft may be required because of trauma resulting in incisional rupture, central scarring not responsive to phototherapeutic keratectomy, irregular astigmatism, contact lens intolerance, or progressive hyperopia. The RK incisions can gape or dehisce during penetrating keratoplasty trephination, preventing creation of an even, uniform, and deep trephination. One method for avoiding RK wound gape or dehiscence during keratoplasty is to mark the cornea with the trephine and then reinforce the RK incisions with interrupted sutures outside the trephine mark prior to trephination. If the RK incisions open during the corneal transplant surgery, then X, mattress, or lasso sutures may be required to close these stellate wounds.
Corneal transplantation may also be required after excimer laser surface ablation. However, because of the 6- to 8-mm ablation zones typically used, the corneal periphery is generally not thinned, and transplantation in this situation is usually straightforward.
After LASIK, corneal transplantation may be required to treat central scarring (eg, after infection or with a buttonhole) or corneal ectasia. A significant challenge in this scenario is that most LASIK flaps are larger than a typical trephine size (8 mm). Trephination through the flap increases the risk that the flap peripheral to the corneal transplant wound may separate. This complication may be avoidable through careful trephination and use of a gentle suture technique that incorporates the LASIK flap under the corneal transplant suture. Femtosecond laser trephination theoretically may decrease the risk of flap separation during trephination.
A few cases have been reported of inadvertent use of donor tissue that had undergone prior LASIK. The risk of this untoward event will increase as the donor pool includes more individuals who have undergone LASIK or surface ablation. Eye banks need to develop better methods to screen out such donor corneas. If a post-LASIK eye is inadvertently used for corneal transplantation, the patient should be informed. A regraft may be required to address significant anisometropia or irregular astigmatism.
Corneal transplantation is occasionally required in a patient with intrastromal corneal ring segments. The polymethyl methacrylate ring segments are typically placed near the edge of a standard corneal transplant, so the ring segments may be removed prior to grafting, or—because the ring segments lie within the central 7 mm of the cornea—they may also be left in place and removed in toto with the host tissue or removed at the time of trephination.
Though rare, corneal transplantation after laser thermokeratoplasty or conductive keratoplasty may be required. Trephination should be straightforward in such cases, and the thermal scars should generally be incorporated into the corneal button. Even if the scars are not incorporated and remain peripheral to the new cornea, they should not significantly affect wound architecture, graft healing, or corneal curvature.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.