CORNEA DISEASES & TRANSPLANTS
Cornea, External Disease and Anterior Segment
The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. It plays an important role in focusing your vision. Any condition that affects the cornea can affect the cornea’s ability to help focus light on the retina, and thus affecting one’s ability to see clearly. Since the cornea creates two thirds of the focusing power of the eye, even a small change in the cornea may lead to changes in one’s vision. Conditions of the cornea may be treated with medications or surgery.
After minor injuries or scratches, the cornea usually heals on its own. Deeper injuries can cause corneal scarring, resulting in a haze on the cornea that impairs vision. If you have a deep injury, or a corneal disease or disorder, you could experience:
Pain in the eye
Sensitivity to light
Reduced vision or blurry vision
Redness or inflammation in the eye
Headache, nausea, fatigue
If you experience any of these symptoms, seek help from an eye care professional.
Keratitis is an inflammation of the cornea. Noninfectious keratitis can be caused by a minor injury, or from wearing contact lenses too long. Infection is the most common cause of keratitis. Infectious keratitis can be caused by bacteria, viruses, fungi or parasites. Often, these infections are also related to contact lens wear, especially improper cleaning of contact lenses or overuse of old contact lenses that should be discarded. Minor corneal infections are usually treated with antibacterial eye drops. If the problem is severe, it may require more intensive antibiotic or antifungal treatment to eliminate the infection, as well as steroid eye drops to reduce inflammation.
Any infection in the cornea can lead to scar formation. Scarring can reduce the quality of vision, so prompt diagnosis and treatment of infections is critical.
Fuchs’ dystrophy is a non-inflammatory, inherited condition that may be progressive and may affect both eyes. The internal lining of the cornea, called the endothelium, becomes damaged. If the endothelium does not function properly, fluid accumulates in the cornea, which causes clouding and a slow decrease in vision. Initially patients will notice blurred vision that is worse in the morning and a glare or halos around lights. As the dystrophy progresses, one’s vision can be blurred all day long. Early Fuchs’ dystrophy can be treated with hypertonic saline drops to help remove excess fluid from the cornea. In more advanced cases, surgery to replace the damaged cells may be necessary.
Keratoconus is a progressive thinning of the cornea. It is the most common corneal dystrophy in the U.S., affecting one in every 2,000 Americans. It is most prevalent in teenagers and adults in their 20s.
Keratoconus causes the middle of the cornea to thin, bulge outward, and form a rounded cone shape. This abnormal curvature of the cornea can cause double or blurred vision, nearsightedness, astigmatism, and increased sensitivity to light.
The causes of keratoconus aren’t known, but research indicates it is most likely caused by a combination of genetic susceptibility along with environmental and hormonal influences. About 7 percent of those with the condition have a history of keratoconus in their family. Keratoconus is diagnosed with a slit-lamp exam. Your eye care professional will also measure the curvature of your cornea.
Keratoconus usually affects both eyes. At first, the condition is corrected with glasses or soft contact lenses. As the disease progresses, you may need specially fitted contact lenses to correct the distortion of the cornea and provide better vision.
In most cases, the cornea stabilizes after a few years without causing severe vision problems. A small number of people with keratoconus may develop severe corneal scarring or become unable to tolerate a contact lens. Intacs, intracorneal rings, and corneal crosslinking are new treatment options under investigation to halt the progression of keratoconus. In severe cases, a corneal transplant may be needed due to scarring, extreme thinning or contact lens intolerance. This is a surgical procedure that replaces the keratoconus cornea with healthy donor tissue.
Full Thickness Corneal Transplant (Penetrating Keratoplasty):
A full thickness corneal transplant can be used to treat a wide variety of corneal conditions. In the standard method of performing this procedure, a hand-held surgical blade called a trephine is used to remove a button-shaped section of the central cornea that consists of all the corneal tissue layers. The button is replaced with healthy donated corneal tissue (a graft) from an eye bank. The transplanted tissue is typically sutured into position. The full thickness corneal transplant is an excellent tool for restoring vision, but recovery of best vision can take 6 or as long as 12 to 18 months.
A recent development in full thickness corneal transplants is the use of a femtosecond laser to assist with the procedure femtosecond laser-assisted keratoplasty. The surgeon programs the laser to create precisely shaped incisions, much more intricate than can be accomplished with a trephine, around the edges of the patient’s central cornea and the donor tissue. The incisions interlock like puzzle pieces, allowing the donated tissue to fit snugly on the eye. This has several advantages compared with a full thickness corneal transplant performed with a trephine. Fewer sutures can be used, and they usually can be removed sooner. The graft is more stable and tends to heal more quickly. The eye tends to heal more evenly as well, which results in a less irregular corneal shape, less astigmatism and therefore better vision.
Femtosecond laser-assisted keratoplasty is not for every patient. The peripheral cornea must be clear enough for the laser to properly create the incisions. A detailed analysis of the cornea with specialized imaging devices can determine whether a patient is a good candidate for the procedure. For those who are not good candidates for femtosecond laser-assisted keratoplasty, a standard corneal transplant can still be performed.
Partial Thickness Corneal Transplant:
Instead of replacing the full thickness of the cornea, some patients benefit from a partial replacement. Two types of partial thickness corneal transplants exist. In deep anterior lamellar keratoplasty, or DALK, only a very thin layer of tissue is left and the rest is replaced with donor tissue. Visual rehabilitation is similar to a full thickness corneal transplant. The advantage of a DALK is the lower rate of rejection as compared to the full thickness transplant. In descemet’s stripping automated endothelial keratoplasty (DSAEK) and descemet’s membrane endothelial keratoplasty (DMEK), a smaller amount of tissue is transplanted. These more recently developed technique offers faster visual recovery for patients with corneal swelling caused by endothelial conditions such as Fuchs’ dystrophy. Only a very thin layer of cornea is removed and then replaced with a thin layer of donor cornea. Vision can be restored as quickly as 2 to 3 months.