Damage to the posterior two layers of the cornea, namely the endothelium and the Descemet’s membrane complex can be caused by a hereditary condition known as Fuchs endothelial dystrophy, or by the trauma sometimes occurring with cataract surgery. In both of these conditions the endothelium and Descemet’s Membrane complex are abnormal and result in corneal edema (fluid build-up in the cornea).
In the past these conditions were treated with a full thickness-penetrating graft. A recent advance in treatment involves transplanting only the posterior two layers of the cornea using a healthy endothelium and Descemet’s Membrane from donor eyes from eye banks.
The transparent cornea, which covers the front of the eye, has five layers. Keratoconus makes the centre of the cornea thinner. The cornea then bulges out in a cone shape, making vision blurry. As a rule, the blurred vision cannot be corrected by glasses. In some cases, even hard contact lenses cannot correct it. The condition will worsen over time.
Corneal cross linking (CXL) is a new treatment for keratoconus. This procedure strengthens the collagen fibres in the cornea. It involves a combination of specially formulated drops of riboflavin (vitamin B2) and the use of low doses of UV light. Combining the two in specific doses has been proven to increase the number of collagen bonds in the cornea. The bonds help prevent more thinning and bulging of the cornea.
The corneal cross linking procedure is not meant to improve vision, but to prevent it from getting worse. However, 50 to 70 per cent of people who have this procedure done experience some improvement in their vision. An improvement may not be noticeable for three to four months.
Once the procedure has flattened the cornea, it may be possible to wear contact lenses. In most cases, it prevents the need for a corneal transplant. It is extremely rare for keratoconus to get worse after the cross linking procedure.
Corneal cross linking can be done as an outpatient procedure. It does not require fasting or any other specific preparation before surgery. It will take two to three hours to do both eyes. You will be given a mild sedative and a pain medication. The first step involves removing the corneal epithelium (outer layer of the cornea). Once this is gone, riboflavin drops are administered every two minutes for 30 minutes.
With the epithelium removed, the riboflavin drops can be absorbed well. After the cornea has been saturated with riboflavin, a UV light is used to activate the vitamin.
To promote the healing of the cornea, your eyes will be fitted with bandage soft contact lenses. They protect the eyes, speed healing and reduce irritation. Discomfort may last up to 48 hours after the procedure. During this time, lubricant drops and pain medications can be used to control the discomfort.
Since the surface of the cornea has been disturbed, vision will be blurry and hazy after the procedure. This lasts a week or two. Vision starts to stabilize within a month. The cornea continues to flatten for another three to four months. Since the cornea is continuing to change, vision may blur and vary for three to four months. You may see halos, glares, or dazzle with night vision. After a month, most people can wear contact lenses.
Although the eyes may be sensitive to light after the procedure, sunglasses can reduce this discomfort. Since vision is disturbed, you will need to arrange for transportation for the first one to two weeks after the procedure. It is a good idea to take a week or two off to focus on relaxing and letting the corneas heal. Most people are able to resume regular activities within two weeks.
Your eye surgeon will see you five days after the procedure. The contact lenses are removed and the cornea is checked. Expect follow up visits at four weeks, and three to four months after the procedure.
The only identifiable risk is infection. It is important that you let your surgeon know about any increase in pain or discharge from the eye. Your eyes will also be irritated by smoke and strong perfumes. You must not swim in a chlorinated pool for at least two weeks after the surgery.
In the past, corneal edema was treated with a graft or corneal transplant. Now, these conditions can be addressed by transplanting a healthy endothelium and Descemet’s membrane. It is a simpler procedure, since it involves only layers of the cornea rather than the full thickness. The surgery removes the Descemet’s membrane, replacing it with healthy donor tissue. Donor tissue is available from several eye banks.
New advances in eye care technology are making it easier to restore vision to those with corneal issues. For more information, talk with your vision care team.