The cornea is the clear ‘watch-crystal’ of the eye. It is about the diameter and thickness of a dime. Along with the crystalline lens of the eye, it acts as a lens which focuses images onto the retina. It also acts as a barrier to the outside environment. The cornea stays clear by having a healthy endothelium – the inside layer of the cornea – which pumps ions and fluid out of the cornea.
Corneal transplantation is one of the most successful ophthalmic surgical procedures. It is used to replace an opaque, irregular, or damaged cornea. Corneal transplants are also called corneal grafts. Recent advances in corneal transplant surgery have improved the safety and visual recovery time of this surgery. The most common reasons for corneal transplantation include:
- Corneal swelling or edema – Severe cases are called bullous keratopathy.
- Keratoconus – Thinning, irregularity, and bulging of the cornea.
- Corneal transplant failure – While most corneal transplants stay clear for many years, some corneas fail and require repeat surgery.
- Corneal inflammation or scarring – Examples include infections (due to bacteria, viruses, or fungi), trauma, and chemical injury.
- Corneal dystrophies – Various different conditions, which occur due to genetic predisposition, can affect the corneal clarity.
Surgical Procedure – Standard Corneal Transplant
Corneal transplant surgery is performed as an outpatient procedure in an ambulatory surgical center. General or local anesthesia, with supplemental sedation, may be used. An anesthesiologist or anesthetist is present during the surgery to monitor vital signs and administer any medications needed to make the patient comfortable. A feeling of pressure may be noted, but there is no pain during the procedure.
Once the eye is anesthetized, the eye and the area around the eye are cleansed with an antiseptic solution. A surgical microscope is placed in position. The eyelids are held open with a device that prevents blinking so there is no need for the patient to worry about keeping the eye open during the surgery. Often, a ring-shaped device is attached to help maintain the normal contour of the eye during the surgery. A trephine is used to remove the central portion of the patient’s cornea and a slightly larger trephine is used to remove the central clear cornea from a donor. Stitches (sutures) secure the donor cornea in place.
Surgical Procedure – Endothelial Corneal Transplant
Endothelial corneal transplants are done when the cornea is swollen. Instead of replacing the whole cornea, only the back layer of the cornea is replaced. There are two types of endothelial transplants – DSAEK and DMEK. In DSAEK, the endothelium and a thin layer of the back of the cornea are shaved from the donor. This donor tissue is thin and can be folded, yet it is easily handled, so that it can be inserted through a very small opening on the edge of the eye. The donor tissue is then unfolded and an air bubble is used to secure it to the back of the patient’s cornea. The air bubble disappears within a short time by itself. In DMEK, the donor is ultra-thin and is injected into the eye and carefully unfolded using techniques that do not allow the tissue to be directly touched. The donor is supported with a gas bubble that lasts up to a week, while the donor establishes a bond with the patient’s cornea. Endothelial keratoplasty has several advantages over a standard corneal transplant- faster visual recovery, shorter healing time, and less likely to result in a change in corneal shape (astigmatism).
Dr. Fuerst has been performing successful endothelial keratoplasty since 2006.
Surgical Procedure – Deep Anterior Lamellar Keratoplasty (DALK)
DALK is indicated when there is an opacity of the front layers of the cornea and the endothelial (back) layer is healthy. An air bubble is used to separate the layers. Advantages over standard keratoplasty include faster healing, less chance of rejection, and less astigmatism.
Corneal transplant surgery may be combined with other surgery. Cataract surgery with intraocular lens placement, secondary insertion of an intraocular lens, or intraocular lens exchange are the most common procedures performed at the same time as corneal surgery. A corneal transplant procedure usually takes 30 minutes to 1 hour.
Cornea Donor Tissue Selection
Eyebanks collect, examine, test, and distribute corneas to ophthalmologists for corneal transplant surgery. Dr. Fuerst uses several eyebanks, all certified by the Eye Banking Association of America, for corneal donor tissue. Dr. Fuerst works with the eyebank to find a suitable donor, has the donor prepared by the eyebank for the planned procedure, and arranges to have the cornea sent to the surgical facility.
Tissue matching is not routinely performed or necessary for the majority of corneal transplants. Corneal tissue from donors with conditions which may be transmitted to the recipient is not used for corneal transplant surgery. The Eyebank uses historical information and extensive laboratory testing to allow the use of only suitable donor material.
Postoperative antibiotic eye drops are typically used for one week and corticosteroid eye drops are used for several months – or longer. Over-the-counter analgesics (pain pills) may be taken and are usually needed for only a short time. The stitches get covered with a layer, known as epithelium, very quickly and are not felt by the patient. Eye protection – a shield, glasses, or sunglasses – is worn for at least 30 days to protect the eye from inadvertent trauma after surgery. As long as eye protection is used, most activities may be resumed on the day after surgery; swimming and diving should be avoided for 1 month.
A typical post-operative visit schedule includes visits 1 day, 1 week, and monthly after surgery for 1 year. Visual acuity can vary significantly. Most patients attain at least 20/400 (the big ‘E’ on the chart) within a month. The stitches are usually removed when healing is adequate. This may take up to one year from the surgery. If vision is good with the stitches in place, they do not need to be removed.
In some patients, corneal astigmatism can be reduced in the early postoperative period by suture adjustment or selective suture removal. Achievement of optimal vision may take one year, or longer, because of changing refraction (glasses prescription), slow wound healing, and/or corneal astigmatism. In some patients, earlier and better vision is attained with a contact lens fit over the corneal transplant.
While corneal transplant surgery is highly successful, complications may occur. Complications include infection (intraocular or corneal), intraocular bleeding, wound leak, glaucoma, graft rejection, graft failure, high refractive error (especially astigmatism and/or myopia), and recurrence of underlying corneal disease.
With modern antibiotics and surgical techniques, infection is a rare occurrence. Bleeding may cause a delay in improvement of vision, but almost never results in a permanent vision loss.
Corneal graft rejection occurs in 10% to 20% of patients. Patients may complain of decreased vision, photosensitivity, ocular ache, and ocular redness. Graft rejection is treated with corticosteroid eyedrops, often supplemented with oral corticosteroids for a short time period. In most cases, the graft rejection episode is reversed, and graft clarity returns fully. The graft may fail if the graft rejection was unusually severe or long-standing or after multiple episodes of graft rejection. A repeat corneal transplant is possible, but the long-term prognosis for a clear regraft is somewhat lower than it was for the original graft. There is no limit to the number of times a corneal transplant may be repeated, although it is rare to recommend or perform many repeat surgeries.
The prognosis for a clear, functioning corneal transplant varies by diagnosis. The chance of long-term transplant success is better than 90% for keratoconus, corneal scars, mild to moderate corneal edema, or corneal stromal dystrophies. Success is somewhat lower for inactive viral keratitis. Corneal transplants for active corneal infections and scars due to chemical (alkali) or radiation injury have a much poorer prognosis.
The high rate of success of corneal transplantation is due to many factors. The cornea is considered to be relatively isolated from the body’s immune system, since it is avascular (no blood vessels). Another important factor is the effectiveness of the corticosteroid eye drops used to prevent, or treat, graft rejection.
Refractive Surgery after Corneal Transplantation
Corneal transplant surgery is one of the most successful eye procedures performed. While corneal transplants result in an optically clear cornea in the majority of cases, visual results are not always completely satisfactory because of astigmatism (irregularity) or anisometropia (the eyes have different prescriptions). Several different procedures are available to correct astigmatism and/or anisometropia following corneal transplant surgery. These procedures include the laser-assisted treatments LASIK and PRK, which Dr. Fuerst has offered since 1999. The goal of these procedures after a corneal transplant is to balance the eyes or decrease the need for corrective eyewear. Although the results are not quite as predictable as LASIK and PRK for patients who have not had corneal transplants, most patients find the improvement in uncorrected vision extremely beneficial and are very satisfied. Further advances in refractive surgery, including customized patterns guided by corneal topography or wavefront analysis, will make these procedures even more successful and may even allow treatment of some irregular astigmatism.