Corneal graft failure occurs when a transplanted cornea loses its ability to restore clear vision, often becoming cloudy and affecting a patient’s sight. Though corneal transplantation has helped restore vision for millions of people worldwide, the risk of graft rejection and failure remains a significant challenge in eye care today.

Understanding Corneal Graft Failure

When someone receives a corneal transplant, the hope is that the new tissue will bring back clear sight and improve their quality of life. However, sometimes the transplanted cornea stops working properly. This is called corneal graft failure. It means the transplanted tissue can no longer do its job of keeping the eye clear and helping the person see well.

Corneal graft failure is different from corneal graft rejection, which is a specific immune response where the body’s defense system attacks the transplanted tissue. While rejection can lead to failure, not all graft failures are caused by rejection. A graft might fail for other reasons, such as problems with the cells that pump fluid out of the cornea, infections, or issues with the eye’s surface.

The cornea is normally an immune-privileged tissue, meaning it has special characteristics that help it avoid being attacked by the body’s immune system. The cornea has no blood vessels, which limits how immune cells can reach it. Despite this natural protection, rejection remains the most common cause of corneal graft failure across all studies and reports.^[1]

How Common Is Corneal Graft Failure

Corneal transplantation is the most frequently performed type of human tissue transplant in the world. More than 180,000 corneal grafts are performed every year globally.^[14] In the United States alone, approximately 80,000 corneal transplantations were performed in 2021.^[2] Over the past 55 years, more than a million corneal transplants have restored vision for patients.^[12]

Despite being the most common transplant procedure, corneal graft failure remains a significant concern. In first-time graft recipients whose corneal bed has no blood vessels, the success rate is quite good, with two-year survival rates exceeding 90 percent. However, for patients with high-risk factors for rejection, this success rate drops dramatically to between 35 and 70 percent.^[1]

About one-third of all corneal grafts show signs of a destructive attack by the immune system when they fail. The incidence of graft rejection varies widely depending on the type of transplant procedure used and individual risk factors. For penetrating keratoplasty, which is a full-thickness transplant, long-term graft survival rates range from 52 to 98.8 percent, with rejection rates reported between 14.1 and 33.5 percent in different studies.^[2]

Newer partial-thickness transplant techniques tend to have lower rejection rates. For deep anterior lamellar keratoplasty, success rates range from 77 to 99.3 percent, with rejection incidents between 6 and 19.7 percent.^[2] Corneal graft rejection is the most common cause of graft failure in the late postoperative period, meaning weeks, months, or even years after the surgery.^[2]

Causes of Corneal Graft Failure

The most common cause of corneal graft failure is allogeneic rejection, which means the recipient’s immune system recognizes the donor cornea as foreign tissue and attacks it. This happens despite the cornea being in immune-privileged sites, which normally help protect transplanted tissue from immune attack.^[1]

When rejection occurs, it results in the loss of donor endothelial cells. These are specialized cells on the inner layer of the cornea that are absolutely critical for maintaining corneal transparency. They work like tiny pumps, removing excess fluid from the cornea to keep it clear. Human endothelial cells cannot repair themselves through cell division, so when they are lost during rejection, they cannot be replaced.^[1]

When the density of endothelial cells falls below a critical threshold, the cornea cannot prevent fluid buildup in its layers. This leads to swelling of the cornea, a condition called stromal swelling, which makes the cornea cloudy and vision poor. This cloudiness might happen suddenly during an acute rejection episode that cannot be reversed, or it might develop gradually after one or more rejection episodes that were treated but still caused some cell loss.^[1]

Not all graft failures are caused by rejection. Primary graft failure can occur when a transplanted cornea is swollen and cloudy from the first day after surgery and never becomes clear. This happens within three months of transplantation and has no identifiable rejection cause.^[14] Other causes of graft failure include chronic loss of endothelial cells over time without a clear immune trigger, infections, problems with how the eye surface heals, or severe irregular shape of the cornea that prevents good vision even though the graft tissue remains clear.^[14]

For patients who have had glaucoma tube surgeries, a specific cause of corneal failure can occur when the tube touches the back of the cornea. This mechanical contact can damage the endothelial cells over time, leading to corneal swelling and failure even without rejection.^[3]

Risk Factors for Corneal Graft Failure

Certain factors put patients at much higher risk for experiencing graft rejection and eventual failure. One of the strongest risk factors is having blood vessels grow into the cornea before transplantation. A cornea with extensive blood vessel growth has much easier access for immune cells to reach the transplanted tissue and mount an attack. Patients with a vascularized corneal bed have significantly lower success rates compared to those with clear, vessel-free corneas.^[1]

The number of previous transplants also matters greatly. Each time a person receives a repeat corneal transplant, the chances of success decrease. The survival rates for third and fourth repeat grafts are particularly poor, at only 25 percent and zero percent respectively in some studies.^[9] This happens because each transplant can sensitize the immune system, making it more likely to recognize and reject future grafts.

Patients with certain underlying conditions face higher risks. Those who have experienced chemical burns, particularly alkali burns to the eye, have higher rejection rates. Prolonged inflammation and extensive vascularization of the cornea both compromise the immune privilege that normally protects corneal transplants.^[2]

Other high-risk situations include patients with a history of previous graft rejection, those with glaucoma or other eye conditions requiring additional surgeries, and patients with certain corneal diseases that involve inflammation. Eyes with iris defects, a history of vitrectomy surgery, or active inflammatory conditions also have increased rejection risk.^[2]

Poor adherence to medication after transplant surgery is another important risk factor. Patients who do not consistently use their prescribed anti-rejection medications, particularly corticosteroid eye drops, are at much higher risk for developing rejection episodes. The protective effect of these medications only works when they are used as directed.

Signs and Symptoms of Graft Rejection

Recognizing the signs of graft rejection early is critical because prompt treatment can sometimes reverse the rejection and save the graft. Patients who experience corneal graft rejection typically notice one or more warning symptoms. These include redness of the eye, pain or discomfort, increased sensitivity to light (called photophobia), and decreased vision.^[12]

A decrease in vision is often the symptom that prompts patients to seek care. The vision may become blurry or cloudy, sometimes gradually over days or weeks, or sometimes more suddenly. This happens as the cornea loses its clarity due to swelling or inflammation from the immune attack.

When a doctor examines an eye experiencing rejection, several clinical signs may be visible. The cornea may show swelling or cloudiness, particularly in the transplanted area. There may be inflammation inside the front chamber of the eye. Small white deposits called keratic precipitates may appear on the back surface of the cornea, specifically on the transplanted tissue rather than on the patient’s original cornea.^[12]

Blood vessels at the edge of the cornea may become engorged and more visible. One particularly telling sign is a rejection line, which can appear as a distinct line moving across the cornea. When this line involves the endothelial layer, it is called a Khodadoust line. This line represents the border between areas where endothelial cells have been destroyed by white blood cells and areas that are still clear.^[12]

There are different types of rejection that affect different layers of the cornea. Epithelial rejection affects the outermost layer and appears at the edge of the graft as an elevated ridge that shows up with fluorescein dye. Stromal rejection involves the middle layer and may show whitish infiltrates that can look similar to viral conjunctivitis. Endothelial rejection, the most common type affecting up to 50 percent of rejection cases, involves the critical inner cell layer and is associated with the most serious consequences for graft survival.^[12]

How Corneal Graft Failure Develops

Understanding how graft failure develops requires looking at what happens in the eye at a cellular and tissue level. The cornea normally maintains its transparency through a delicate balance. The endothelial cells on the back surface actively pump fluid out of the corneal tissue. Without this pumping action, fluid accumulates in the cornea’s layers, causing it to swell and become cloudy.

In a healthy transplanted cornea, the donor endothelial cells continue this pumping function. However, when rejection occurs, the recipient’s immune system recognizes certain markers on the donor cells as foreign. T cells and other immune cells travel to the cornea and begin attacking the donor tissue. This immune attack is particularly devastating to endothelial cells.

Because human endothelial cells cannot divide and multiply to replace lost cells, any destruction is permanent. The cornea starts with a certain number of endothelial cells, and this number can only decrease over time, never increase. During a rejection episode, large numbers of these critical cells can be destroyed in a short period.^[1]

When enough endothelial cells are lost, the remaining cells cannot adequately pump fluid out of the cornea. The tissue becomes waterlogged and swollen. This swelling disrupts the normally precise arrangement of collagen fibers in the cornea that allows light to pass through clearly. As a result, the cornea becomes cloudy, and vision deteriorates.

Sometimes this process happens suddenly during an acute rejection episode. The eye becomes red and painful, and vision drops quickly as the cornea swells. Other times, the process is more gradual. A patient might have one or more rejection episodes that are treated and appear to resolve, but each episode causes some permanent loss of endothelial cells. Eventually, the cell count drops below the critical threshold needed to maintain clarity, and the cornea slowly decompensates over months or years.

The immune privilege that normally protects the cornea can be lost or compromised under certain conditions. When blood vessels grow into the cornea, they provide a highway for immune cells to reach the transplanted tissue. Chronic inflammation, extensive tissue damage, or repeated surgeries can also break down the protective mechanisms that usually keep immune responses in check.^[2]

Even in successful transplants, there is ongoing gradual loss of endothelial cells over time. This happens at a faster rate in transplanted corneas compared to natural corneas. While many grafts maintain adequate cell counts for years or decades, this gradual decline means that even grafts that have never experienced obvious rejection may eventually fail as cell density drops below the critical level needed for corneal clarity.

Prevention Strategies

Preventing corneal graft rejection and failure begins even before the transplant surgery. For patients identified as high-risk, doctors may recommend more aggressive prevention strategies. The cornerstone of rejection prevention is the consistent use of medications, particularly corticosteroid eye drops, after transplantation.

Topical corticosteroids work by suppressing the local immune response in the eye. These drops must be used exactly as prescribed, often multiple times daily in the period immediately after surgery, then gradually reduced to a lower maintenance dose that may need to be continued for years or even indefinitely. Patient adherence to this medication regimen is crucial for preventing rejection.

For high-risk patients, additional immunosuppressive medications may be recommended. These can include topical medications like cyclosporine or tacrolimus, which help prevent the immune system from attacking the graft. Some patients may require systemic immunosuppressive medications taken by mouth, though these carry more potential side effects and require careful monitoring.

The choice of surgical technique can also impact rejection risk. Newer partial-thickness transplant procedures that replace only the diseased layers of the cornea, rather than the full thickness, have shown lower rejection rates in many cases. For patients with disease limited to the endothelial layer, procedures like Descemet stripping endothelial keratoplasty or Descemet membrane endothelial keratoplasty may offer better outcomes with less rejection risk compared to traditional full-thickness penetrating keratoplasty.^[12]

Regular follow-up care is essential for all transplant recipients. Scheduled examinations allow doctors to monitor the health of the graft, check for early signs of rejection, and adjust medications as needed. During these visits, doctors can also ensure that the patient understands how to properly use their medications and recognize warning signs of problems.

Protecting the eye from injury is another important preventive measure. Trauma to the transplanted cornea can trigger inflammation and increase rejection risk. Patients should wear protective eyewear during activities that could result in eye injury. Prompt treatment of any eye infections or inflammation is also important, as these conditions can trigger or worsen rejection responses.

Some research has explored whether tissue matching between donor and recipient might reduce rejection risk. However, unlike organ transplants such as kidney or heart transplants, corneal transplantation does not routinely involve matching for blood type or tissue compatibility markers. The relative immune privilege of the cornea and practical challenges in tissue matching for time-sensitive corneal transplants have meant that any suitable donor cornea can be used, regardless of matching.^[12]