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Millions of people around the world suffer vision loss that is irreversible, so eye doctors have worked to replace parts of the eye for centuries. While whole-eye transplants are currently not feasible, some parts of the eye can be successfully replaced with donor tissue.
Corneal transplants are the most common and successful form of eye tissue transplant. When someone refers to an eye transplant, they usually mean corneal transplant. However, there are some other types of eye tissue transplants, a few of which are still in development.
Thanks to advances in organ donation and transplantation, the understanding of eye transplants is improving. Researchers hopes that whole eye transplant will become feasible in a decade.
Like any surgery, there are risks to eye tissue transplants, but these forms of surgery, particularly corneal transplants, can be life-changing for the recipient.
Does an Eye Transplant Replace the Whole Eye?
With over 37 million people around the world suffering irreversible vision loss, being able to transplant an entire eye to a new person seems like a great solution.
Although eye transplants are performed, this procedure does not involve the entire eye. Instead, there are parts of the eye that can safely be transplanted to a different person, and most eye transplants are actually corneal transplants.
Whole-eye transplants (WET) are both experimental and controversial, but medical researchers are working on this technology.
What Is a Corneal Transplant?
A corneal transplant involves replacing the clouded cornea with a clear donor cornea. The donor cornea is collected from individuals who have willingly donated their eyes to benefit others. Donor corneas are stored freshly in eye banks regulated by FDA.
Corneal surgeries have success rates of more than 95%. The main reason behind these success rates is because the cornea has few tissues, minimizing the risk of rejection. New transplantation techniques have also lowered rejection rates.
Corneal blindness is a condition where other parts of the eye function properly, except for the cornea. Unfortunately, despite more than 10 million people having corneal blindness globally, only 100,000 corneal transplants are performed yearly, primarily because of a shortage of donor tissues. That aside, donor transplants are also rejected by the host's body, further lowering the number.
Some eye conditions that necessitate corneal transplant include:
- Keratoconus, cone-shaped cornea instead of the normal dome shape
- Complications from previous corneal surgery or other eye surgeries that affected the cornea
- Eye infection and injuries that damage the cornea
- Fuchs' dystrophy
- Penetrating keratoplasty (PK): This is the older form of corneal transplant, but it works well and is still performed often. During the transplant, you will most likely be awake with local anesthesia. Your doctor will remove a small piece of your cornea, and the donated tissue will replace what was removed, then sutured or stitched into place.
- Lamellar keratoplasty (LK): With LK, the inner and outer layers of the cornea are replaced rather than all layers as with PK. There are a few different techniques used in LK, which depend on how the donor tissue is prepared. All approaches to LK have a faster recovery time and fewer complications after the operation.
At your follow-up visit, your eye doctor will remove stitches if they are present and examine your eye for any potential complications.
Full recovery and vision return take about a year because it takes a long time for new tissues to integrate with your eye and for the swelling in the area to go down. You may still need glasses, contact lenses, or a laser surgery like LASIK to change refractive errors, but you will be able to see clearly thanks to the new cornea.
There are risks to both forms of cornea transplant. The main complication would be rejection of donor tissue. Your doctor may prescribe drugs to ease the body into working with this new tissue.
The following are other risks associated with corneal transplants:
- Infection in the eye
- Glaucoma, or high eye pressure that leads to retinal damage
- Loss of vision
- Scarring on the surface of the eye that clouds vision
- Swelling of the cornea
Other Eye Transplant Surgeries
Other types of eye transplant procedures, some of which are still in the early stages, include:
- Amniotic Membrane Transplantation (AMT). This is a well-established surgery. The amniotic membrane is replaced to treat problems affecting the sclera, the outer layer or “white” of the eye, and the conjunctiva, the clear tissue covering the white part of the eye.
- Eyelash transplants. Eyelashes do not need to be long to be effective, but they are an important part of the eye’s overall system, helping to maintain the microbiome. If eyelashes are lost due to injury, burns, medical conditions, or radiation treatment, they can be replaced with transplant surgery.
- Tear duct replacement. This procedure is still in its early phases, but in 2010, French eye surgeons transplanted eyelids with tear ducts as part of a full-face transplant. Eyelids with tear ducts have also been part of other transplants in the past few years. For people who suffer problems with clogged or insufficient tear ducts, this transplant could change how their eyes manage moisture.
- Retinal pigment epithelium transplant. Some early retinal cell testing has been very successful. In clinical trials, researchers have used human stem cells to create retinal pigment epithelial (RPE) cells, which can be beneficial for those suffering from macular degeneration or other conditions that involve degradation and loss of cells in the retina.
Whole Eye Transplant Is Still Experimental
According to the National Eye Institute (NEI) in 1977, the difficulties presented by transplanting the entire eye included:
- Keeping proper blood circulation in the transplanted eye during and after the operation.
- Immune system rejection of foreign tissue.
- Cutting the optical nerve and incorporating that into another person’s optic nerve.
As surgery techniques improve, the first two issues are being managed in different ways in different organ transplants. Nerve regeneration techniques are becoming more available to assist with connecting a new optic nerve.
In 2016, a team of surgeons aimed to perform a whole eye transplant, but studies conducted on laboratory mice and other animals found that cell growth was an important issue. Essentially, convincing cells not to die off completely and to regenerate when they were placed in a new environment was the crux of the problem.
While a WET has still not been conducted successfully yet, there is hope that within a decade, this technology will become possible.
Eye Surgery Success and Risks
Despite unmatched success rates of a corneal transplant and other eye surgeries, organ rejection is the main challenge associated with these procedures. Organ rejection occurs if your body's immune system does not recognize the transplanted tissue and attacks it.
Corneal rejection occurs in three out of 10 patients who undergo full-thickness transplants. Rejection risks are lower in partial-thickness surgery patients. Warning signs of impending rejection include:
- Sudden eye pain
- Hazy or cloudy vision
- Redness in the eye
- The eye becomes extra sensitive to light
You should inform your eye surgeon if you have any of these symptoms after a corneal transplant. That aside, corneal transplants may also cause other eye problems, such as bleeding, infection, detached retina, and glaucoma.
Even if the transplant works as expected, other eye problems, such as macular degeneration, diabetic retinopathy, and astigmatism can impair your vision.
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