Corneal Transplant Surgery


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Corneal transplant surgery (also known as corneal graft surgery), is an operation where the diseased part of your cornea (usually the central cornea) is removed and replaced with a similar matching piece of healthy cornea from a donor eye. The graft is usually held in place by fine sutures which are left in the eye until the cornea is adequately healed. Grafts can be full thickness (where the entire 5 layers of cornea are replaced) or partial thickness (where only certain layers are replaced).


(Image adapted from the internet)


The cornea is the clear, front window of the eye. A normal, healthy cornea is transparent and clear; this allows light to enter the eyeball. Light entering the eye passes through the clear cornea and clear lens to become focused onto the retina at the back of the eye. A clear cornea is therefore essential for you to have good vision.

When the cornea is damaged from injury or disease, it becomes scarred and/or cloudy. This prevents the light entering the eye from being focused precisely onto the retina. As a result, what you see becomes blurred, distorted and patchy. This can be severe enough to even cause blindness. Damage to the cornea can also cause significant pain and discomfort. This is because the cornea is full of nerve fibres, including those that transmit the sensation of pain. Pain from the cornea can be very intense.



WHEN IS A CORNEAL TRANSPLANT REQUIRED?

Corneal transplant surgery has been performed since the early 1900s. Of all transplant operations, it is one of the most successful and most common, with over 40,000 cornea transplants performed in the United States every year.

In general, there are 3 main reasons for you to have a corneal graft:
      1. Optical - to improve vision
      2. Therapeutic - to remove inflamed cornea and relieve pain
      3. Tectonic - to repair a perforation of your cornea

Not all diseases of the cornea require treatment with a corneal transplant. Most of the time, treatment with eye drops, tablets, spectacles or contact lenses are all that are needed to deal with the problems associated with the corneal disease.

The commonest corneal diseases requiring corneal grafting include pseudophakic bullous keratopathy (permanent cloudiness of the cornea after cataract surgery), keratoconus, corneal dystrophy, excessive corneal scarring, herpes infection of the cornea, complications after laser refractive surgery, trauma and chemical injury.



TYPES OF CORNEAL TRANSPLANT PROCEDURES

As stated above, corneal grafts can be full thickness or partial thickness. Broadly speaking, there are 3 main types of corneal transplant procedures: penetrating keratoplasty (full thickness), lamellar keratoplasty (partial thickness), and endothelial keratoplasty (partial thickness).

Penetrating keratoplasty: This is the conventional method of performing a corneal graft. In penetrating keratoplasty, a round button-shaped full-thickness section of unhealthy corneal tissue is removed from your eye. A similar sized, full thickness, healthy, donor corneal tissue is then used to cover the resulting gap in your cornea. This type of procedure is useful for conditions where the entire corneal structure has been affected and in trauma causing perforation.

Just imagine the scarred cornea as a badly scratched window in a room. It is not possible to remove and replace the entire window. Instead, a round circle is cut through the center part of the scratched window. The round circle of scratched glass is replaced by a similarly sized round circle of clear and unscratched glass, thus allowing you to see outside clearly again.





Lamellar keratoplasty: Sometimes, only certain layers of the cornea are diseased. A full-thickness graft can still be performed, but some may prefer a partial thickness graft where only the diseased layers are replaced and the healthy layers are left intact.

For example, lamellar keratoplasty may be suitable for corneal scarring involving only the front layers of the cornea. In this situation, a lamellar keratoplasty procedure will only replace the scarred front layers of the cornea while leaving the healthy layers at the back of the cornea intact.





Endothelial keratoplasty: The endothelium is the innermost layer of the cornea. When the endothelium is damaged, such as during complicated cataract surgery, this can cause the rest of the cornea to become swollen and cloudy. In this situation, an endothelial keratoplasty is appropriate because only the diseased endothelium is removed and replaced with healthy donor endothelium.

This technique of corneal transplantation is relatively new. After the diseased endothelium is removed, healthy new endothelium is floated into the correct position. An air or gas bubble is inserted into the eye to keep the endothelium in place. No stitches are required. The main benefit of this procedure is that most of your natural corneal shape and strength remains intact. This translates to better vision outcomes and less risk of complications compared to penetrating keratoplasty.






WHAT TO EXPECT DURING CORNEAL TRANSPLANT SURGERY

Once the decision has been made to have corneal transplant surgery, a donor cornea needs to be ordered. Donor corneas come from volunteers who, prior to their deaths, have agreed to donate their healthy corneas to those who require them. How long you need to wait for a donor cornea will depend on your local eye bank. In the United States, the waiting time is generally 1 to 2 weeks.

Donor corneal tissue comes from volunteers who, before they die, agreed to donate their eyes to those who need them. Donated eyes will be processed and meticulously screened by the local or national eye bank to ensure that they are healthy, optically clear, and suitable for use in a transplant. In particular, the eyes are checked to make sure they are free from transmissible disease, including HIV and hepatitis.

Corneal transplant surgery is usually performed on an outpatient basis. You will not need to stay overnight at the hospital unless there is a reason for hospitalization. You can choose to have surgery to be done either under general or local anesthesia. With local anesthesia, an injection will be given around the eye to numb it. You will be awake throughout the entire procedure, but you should not feel any pain.

Once anesthesia has taken effect, a speculum is used to hold your eyelids open. Measurements are then made to determine the amount of diseased cornea to remove and the size of donor tissue required to replace it. After the button-shaped section of tissue is removed from your diseased cornea, the healthy donor tissue (cut to a button shape) is sutured in its place (see right). Corneal graft surgery usually takes 1 to 2 hours to perform.

(Image adapted from the internet)



WHAT TO EXPECT AFTER CORNEAL TRANSPLANT SURGERY

In the early days, your eye will be sore, watery and sensitive to light. You will be given antibiotic and steroid eye drops to help improve comfort, prevent infection, decrease inflammation and promote healing. Initially, these drops will need to be put in your eye hourly or 2-hourly, but will be reduced over a few weeks. In some people, the steroid eye drops need to be continued over several months. Avoid heavy exercise and lifting for at least one month, and make sure you do not inadvertently rub or apply pressure onto your eye.

The vision in your operated eye will be blurred for around 12 months after surgery. Your vision will slowly improve as the eye heals. By 3 months, the shape of your cornea will have stabilized to a certain extent and your refraction can be tested. Spectacles or contact lenses can be prescribed as early as 6 months after surgery to help you see better. If you have high amounts of corneal astigmatism, some of the sutures may be removed in stages to reduce it. It can take up to two years (when most, if not all, the sutures will have been removed) for your vision to stop fluctuating and achieve its best visual outcome. Laser vision correction may be appropriate in some cases to improve your vision further.

As with all surgery, a corneal transplant operation also comes with its own risk of corneal transplant complications. These include astigmatism (both regular and irregular), cataract, glaucoma, persistent inflammation and rarely, endophthalmitis (severe infection affecting the entire eyeball). Always make sure you instil your eye drops and look after your graft as instructed by your ophthalmologist.

An example of corneal graft rejection. One of the characteristic signs of graft rejection is the Khodadoust line (black arrow), which is the accumulation of inflammatory cells at the corneal endothelium. Symptoms include redness of the eye, reduced vision and light sensitivity. If you notice any of these symptoms, consult your ophthalmologist immediately.

(Image adapted from the internet)


One complication that you must always consider is corneal graft rejection. Corneal graft rejection develops when your body recognizes the graft as foreign and tries to mount an immune response against it. This occurs in around 10% to 20% of patients. Rejection can happen at any stage after surgery, even after many years of not having any problems. If detected early, it can be treated and the process reversed successfully. Because of this risk, you will need lifetime follow-up for your corneal graft.

Research on the long term outcomes of corneal grafts has shown that 2 of 3 full-thickness grafts tend to remain clear for 5 years or more. If a repeat transplant is needed, only half will remain clear for 5 years or more. Around 75% of corneal transplants result in improved vision. However, the remaining 25% will either develop worse vision or not notice any visual improvement.




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