(Corneal Graft; Penetrating Keratoplasty; Endothelial Keratoplasty)
Corneal transplantations are done for several reasons:
To reconstruct the cornea (eg, replacing a perforated cornea)
To relieve intractable pain (eg, severe foreign body sensation due to recurrent ruptured bullae in bullous keratopathy)
To treat a disorder unresponsive to medical management (eg, severe, uncontrolled fungal corneal ulcer)
To improve the optical qualities of the cornea and thus improve vision (eg, replacing a cornea that is scarred after a corneal ulcer, is clouded because of edema as occurs in Fuchs dystrophy or after cataract surgery, is opaque because of deposits of nontransparent abnormal corneal stromal proteins as occurs in hereditary corneal stromal dystrophy, or has irregular astigmatism as occurs with keratoconus)
The most common indications are the following:
Tissue matching is not routinely done. Cadaveric donor tissue can be used unless the donor is suspected of having a communicable disease.
Corneal transplantation can be done using general anesthesia or local anesthesia plus IV sedation.
Topical antibiotics are used for several weeks postoperatively and topical corticosteroids for several months. To protect the eye from inadvertent trauma after transplantation, the patient wears shields, glasses, or sunglasses. If transplantation involves the full thickness of the cornea (as in penetrating keratoplasty, or PKP), achievement of full visual potential may take up to 18 mo because of changing refraction with wound healing and after suture removal. Only the corneal endothelium needs to be transplanted in diseases where the corneal stroma is clear, has a smooth stromal surface with a regular curvature, and only the corneal endothelium is not functioning well (eg, Fuchs dystrophy, bullous keratopathy resulting from cataract surgery). In corneal endothelium transplantation (eg, Descemet stripping endothelial keratoplasty [DSEK]) or the newest technique, Descemet Membrane Endothelial Keratoplasty (DMEK), achievement of full visual potential usually occurs by 6 mo or 3 mo respectively. In many patients, earlier and better vision is attained by wearing a rigid contact lens over the corneal transplant.
Complications include the following:
Graft rejection rates are usually < 10% (eg, in patients with early bullous keratopathy), but may be up to 68% in higher-risk patients (eg, those with chemical injury). Rejection symptoms include decreased vision, photosensitivity, ocular ache, and ocular redness. Graft rejection is treated with topical corticosteroids (eg, prednisolone 1% hourly), sometimes with a supplemental periocular injection (eg, triamcinolone acetonide 40 mg). If graft rejection is severe or if graft function is marginal, additional corticosteroids are given orally (eg, prednisone 1 mg/kg once/day) and occasionally IV (eg, methylprednisolone 3 to 5 mg/kg once). Typically, the rejection episode reverses, and graft function returns fully. The graft may fail if the rejection episode is unusually severe or long-standing or if multiple episodes of graft rejection occur. Regraft is possible, but the long-term prognosis is worse than for the original graft. Keratoprosthesis (artificial cornea) can be placed if grafts fail repeatedly.
The chance of long-term transplant success is
The generally high rate of success of corneal transplantation is attributable to many factors, including the avascularity of the cornea and the fact that the anterior chamber has venous drainage but no lymphatic drainage. These conditions promote low-zone tolerance (an immunologic tolerance that results from constant exposure to low doses of an antigen) and a process termed anterior chamber–associated immune deviation, in which there is active suppression of intraocular lymphocytes and delayed-type hypersensitivity to transplanted intraocular antigens. Another important factor is the effectiveness of the corticosteroids used topically, locally, and systemically to treat graft rejection.
Corneal limbal stem cell transplantation surgically replaces critical stem cells at the limbus (the area where the conjunctiva meets the cornea). Host stem cells normally reside in this area. Transplantation is done when the host stem cells have been too severely damaged to recover from disease or injury.
Conditions such as severe chemical burns, Stevens-Johnson syndrome, and severe damage caused by chronic contact lens overwear may cause persistent nonhealing corneal epithelial defects. These defects result from failure of corneal epithelial stem cells to produce sufficient epithelial cells to repopulate the cornea. If untreated, persistent nonhealing corneal epithelial defects are vulnerable to infection, which can lead to scarring, perforation, or both. Under these circumstances, a corneal transplant, which replaces only the central cornea and not the limbus, is insufficient. Stem cells are needed to produce new cells that repopulate the cornea, restoring the regenerative capacity of the ocular surface.
Corneal limbal stem cells can be transplanted from the patient’s own healthy eye or from a cadaveric donor eye. The patient’s damaged corneal epithelial stem cells are removed by a partial-thickness dissection of the limbus (ie, all the epithelium and the superficial stroma of the limbus). Donor limbal tissue, which is prepared by a similar dissection, is sutured into the prepared bed. Systemic immunosuppression is required after cadaveric limbal grafts.