The eye is an incredibly complex and intricate organ that allows us to see the world around us. Even after death, certain parts of the eye can be donated to help restore sight to the blind. This article will examine which specific parts of the eye are able to be donated after death.
The Cornea
The most commonly donated part of the eye is the cornea. The cornea is the clear, dome-shaped surface that covers the front of the eye. It is a powerful refractive surface that focuses light as it enters the eye and accounts for approximately 2/3 of the eye’s focusing power. The cornea does not contain any blood vessels – it gets oxygen directly from the air. This lack of blood vessels allows the cornea to be transplanted without the high risk of rejection that blood vessels would pose.
There are several conditions that can damage the cornea and cause blindness, including infections, trauma, and degenerative diseases. A corneal transplant involves surgically replacing the damaged cornea with healthy donated corneal tissue. It is one of the most common and most successful transplant procedures. In the United States, about 48,000 corneal transplants are performed each year. The survival rate of corneal transplants exceeds 90% after five years. Transplant patients experience restored vision once the surgery heals.
To be eligible for corneal donation, the donor’s eyes must be harvested within 6-12 hours after death. The cornea is extremely sensitive, so timely removal is critical. After removal, the corneal tissue is evaluated and stored in preservatives until transplantation. With proper harvesting and storage techniques, corneal tissue can be stored for up to 14 days from the time of donation.
Advantages of Corneal Transplants
- Minimally invasive procedure
- High success rate
- Rapid healing and visual rehabilitation
- Low risk of rejection
The Sclera
The sclera is the tough, opaque white outer coating of the eye that covers most of the eyeball. Also known as the “white of the eye”, the sclera provides structure and protection for the inner workings of the eye. The only parts of the eye not covered by the sclera are the cornea and the thin tissue over the drainage angle. The sclera is composed of dense fibrous connective tissue consisting mostly of collagen.
Donated scleral tissue can be used to treat a variety of ocular conditions. Scleral reinforcement procedures use processed donor scleral tissue to treat scleral thinning disorders and strengthen the structural integrity of the eye. Scleral graft transplantation involves replacing a damaged portion of the sclera with healthy donor tissue. This treatment is used for severe eye traumas when part of the sclera is missing or severely damaged. Scleral contact lenses are large specialty lenses made from rigid gas permeable plastic that rest on the sclera. Donor scleral tissue can be used to customize the fit of these lenses.
To be suitable for donation, scleral tissue must be carefully dissected from the eye within 24 hours of death. The harvested tissue is treated with antibiotics, sterilized, and preserved in storage medium under refrigeration. It can be stored for up to 4 weeks before transplantation.
Advantages of Scleral Donation
- Maintains the structure and shape of the eye
- Strengthens a weakened sclera
- Customizes scleral contact lenses
- Treats severe ocular traumas
Extraocular Muscles
There are six extraocular muscles that control eye movement: four rectus muscles (superior, inferior, medial, and lateral) and two oblique muscles (superior and inferior). These muscles originate at the back of the eye and connect to the outer surface of the white part of the eye (sclera). When these muscles contract, they move the eye up, down, left, and right.
Donated extraocular muscles can be used to treat certain eye movement disorders. In a procedure called eye muscle transplantation, damaged or nonfunctional eye muscles are replaced with healthy donor muscles. This restores normal eye movement in patients with paralyzed eye muscles caused by neurological conditions or trauma.
To harvest viable extraocular muscles, the eye globe must be removed shortly after death, within 24 hours. The harvested muscles are dissected, treated with antibiotics, and refrigerated in preservative solution for up to 10 days until transplantation. Not all donor extraocular muscles meet the strict criteria to be suitable for transplant.
Advantages of Extraocular Muscle Transplantation
- Restores eye mobility
- Treats paralyzed eye muscles
- Allows for normal eye alignment and movement
- Improves vision in some cases
Fatty Tissue
Orbital fat is the soft, cushioning fatty tissue that surrounds the eyeball in the eye socket (orbit). This fat provides protective padding for the delicate structures of the eye and allows the eyeball to move freely. Orbital fat can be donated after death and used as filler for facial rejuvenation procedures.
The most common clinical use of donated orbital fat is for correcting a sunken appearance around the eyes. Sunken eyes can occur naturally with age or after an injury or surgery around the eye. Injected donor fat can fill the hollow areas around the eyes and restore a smoother, more youthful appearance.
To collect viable orbital fat, the fatty tissue surrounding the eyeball must be carefully removed within 24 hours after death. The harvested fat is processed, sterilized, and stored frozen until transplantation. When properly handled, donor orbital fat can be safely stored for over a year.
Advantages of Donated Orbital Fat Transfer
- Natural-looking and long-lasting filler
- No risk of allergic reaction
- Minimally invasive injections
- Smooths hollows under the eyes
The Retina
The retina is the innermost light-sensitive tissue lining the back of the eye. It contains photoreceptor cells called rods and cones that detect light and convert it into signals that are transmitted to the brain, enabling sight. Though less common than corneal transplants, retinal transplant surgeries are performed to treat certain retinal diseases that result in blindness.
Candidates for retinal transplant include those with retinitis pigmentosa, macular degeneration, diabetic retinopathy, retinal detachment, and traumatic injuries. During the procedure, the damaged retina is surgically removed and replaced with healthy donated retinal tissue. However, retinal transplants are very challenging – the retina is extremely delicate and complex. Graft survival rates and visual outcomes are not yet as favorable as other types of transplants.
To collect viable retinal tissue for transplantation, the donor’s eyes must be enucleated within 6 hours of death and kept refrigerated. The retina is carefully dissected from the back of the eyeball and stored in preservative solution until transplantation. Retinal tissues can be maintained for 3-7 days under proper conditions.
Potential Benefits of Retinal Transplantation
- May restore vision in certain blindness cases
- Replaces diseased retinal cells with healthy tissue
- Treatment option when other therapies fail
The Optic Nerve
The optic nerve is actually part of the central nervous system that transmits visual information from the retina to the brain, allowing us to see. Each optic nerve originates at the very back of the eye and carries nerve impulses stimulated by the retina. Though optic nerve transplantation is still highly experimental, research is underway to assess its potential for restoring vision.
In optic nerve transplant surgery, a donated segment of optic nerve tissue is implanted into a patient whose optic nerve is damaged. This offers hope to patients blinded by optic nerve injuries or diseases. However, there are formidable technical obstacles – successful fusion of the donor nerve with the recipient’s damaged nerve is very difficult.
For donation, the optic nerve must be carefully extracted from the donor’s eye within 24 hours of death. The harvested nerve segment is cleansed, sterilized, and stored in special preservative solutions until transplant. With proper handling, optic nerve tissue has been maintained for up to 3 weeks.
Potential Applications of Optic Nerve Transplantation
- May restore vision after optic nerve damage
- Could aid recovery from traumatic optic nerve injuries
- Experimental treatment for optic neuropathies
Conclusion
Although the eye cannot be transplanted in its entirety after death, certain components can be donated to help restore sight to the blind. The cornea is by far the most commonly donated and transplanted part of the eye. Other eye structures like the sclera, extraocular muscles, orbital fat, retina, and optic nerve also offer potential for transplantation in specialized cases. With proper techniques for timely harvesting and storage after death, these eye tissues can be used to give the gift of renewed vision.