The cornea is the clear, dome-shaped front window of the eye that focuses light onto the retina. When this tissue becomes clouded or misshapen due to disease or injury, vision is severely compromised. A corneal transplant, formally known as keratoplasty, replaces the diseased or scarred corneal tissue with healthy, clear tissue from a human donor. This procedure restores clarity to the visual pathway, improving sight and sometimes alleviating pain. Unlike a permanent synthetic lens implant, a corneal graft is biological donor tissue, meaning its lifespan is not indefinite.
General Expectations for Graft Survival
A successful corneal transplant is not a permanent solution, but modern techniques offer excellent long-term outcomes. The overall survival rate for a first-time penetrating keratoplasty (PK), the traditional full-thickness transplant, is high, with approximately 82% of grafts remaining clear and functional at ten years. This rate is heavily influenced by the underlying condition that necessitated the surgery.
Transplants performed for conditions with a low immunological risk generally have the best prognosis. For example, grafts correcting Keratoconus, where the cornea thins and bulges outward, show survival rates exceeding 90% after ten years. Conversely, eyes with pre-existing inflammation, extensive corneal blood vessels, or previous glaucoma surgery are considered high-risk. The duration of a clear graft is highly variable, ranging from a few years in complex cases to several decades in low-risk patients.
How Different Procedures Affect Lifespan
The specific surgical technique significantly impacts the graft’s longevity and the primary cause of its eventual failure. Full-thickness transplants, or Penetrating Keratoplasty (PK), replace all layers of the cornea. PK requires numerous sutures and creates a large wound, making it susceptible to a higher rate of immune rejection that can destroy the graft quickly.
Newer, partial-thickness procedures, known as Endothelial Keratoplasties (EK), only replace the innermost, damaged cell layer. Descemet Membrane Endothelial Keratoplasty (DMEK) and Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) are favored for endothelial diseases like Fuchs’ dystrophy because they leave the patient’s healthy outer corneal layers intact. DMEK has the lowest rate of immune rejection, recorded at less than 10% over ten years, compared to PK’s higher risk.
Despite the lower rejection risk, EK procedures have a different long-term limitation related to the donor tissue itself. The endothelial cells, which keep the cornea clear, are non-replicating and naturally decrease in number over time. Some studies suggest that surgical trauma or accelerated cell loss following EK procedures may lead to late graft failure due to cell exhaustion, even if the graft is never rejected. This failure mode is a slow process that typically occurs many years after the initial surgery.
Primary Causes of Graft Failure
A clear corneal graft stops functioning when the donor tissue loses its transparency, driven primarily by immune rejection or disease recurrence. Immune rejection occurs when the host’s body recognizes the donor tissue as foreign and mounts an attack against it. This T-cell mediated response leads to the destruction of the donor endothelial cells.
The destruction of the endothelial cell layer is often irreversible, causing the cornea to swell and become cloudy. This requires immediate and aggressive anti-rejection steroid drops. Eyes with pre-existing inflammation or blood vessels in the cornea are at the highest risk for this immunological failure. Recognizing the warning signs of rejection—redness, light sensitivity, pain, and decreased vision—is essential for timely intervention.
The other main cause of failure is the recurrence of the original disease in the new donor tissue. For example, the Herpes Simplex Virus (HSV), which remains latent in the host’s nerve tissue, can reactivate due to surgical stress or post-operative steroid use, causing a viral infection in the new graft. In high-risk cases, continuous prophylactic oral antiviral medication is often necessary to suppress the virus. Fuchs’ dystrophy does not recur in the donor tissue, but other genetic conditions like lattice or granular corneal dystrophies can recur as the host’s defective cells eventually migrate into the donor tissue.
Options Following Transplant Failure
When a corneal graft fails, the primary option for restoring vision is a repeat keratoplasty, or re-transplantation. Each subsequent transplant carries a progressively lower chance of success due to increased inflammation and scarring from previous surgeries. While a first-time PK has a high ten-year survival rate, a repeat PK has a lower five-year survival rate, often reported between 49% and 64%.
The presence of factors like pre-existing glaucoma or a history of previous rejection episodes further decreases the viability of a repeat transplant. For patients who have experienced multiple graft failures or severe underlying ocular surface disease, an artificial cornea, or keratoprosthesis (KPro), becomes the preferred alternative. The Boston Keratoprosthesis is the most common device used in these complex cases.
The KPro bypasses the body’s immune system entirely by replacing the cornea with a synthetic material. This offers a durable solution in eyes where donor tissue would almost certainly fail. The retention rate for the KPro in high-risk eyes is significantly better than for repeat biological transplants, with rates around 80% at four years. While it carries a risk of specific complications, such as glaucoma and infection, the artificial cornea offers the best chance for long-term vision.