There are several corneal dystrophies. The most common is anterior basement membrane corneal dystrophy (ABMD). It is also known as map or dot or fingerprint corneal dystrophy. It is frequently associated with another corneal problem – recurrent erosions.
In Anterior Basement Membrane Dystrophy (ABMD), the basement membrane under the corneal epithelium does not function properly. The epithelium is a thin layer of surface skin covering the cornea (as well as the whole body). The basement membrane functions as a sticky anchor over which the epithelium grows. The basement membrane stabilizes the epithelium.
There are generally two conditions which cause basement membrane dysfunction – one inherited, and one acquired by a deep corneal abrasion (scratch) which damages the basement membrane. This condition is common, treatable, and rarely leads to significant vision loss.
What are the symptoms of ABMD?
Most patients who have ABMD don’t have any symptoms. However, when the basement membrane doesn’t stabilize the epithelium properly, two sets of symptoms may occur.
The first is called recurrent erosion, which describes a situation when recurrent abrasions (scratches) develop on the cornea. Because the epithelium isn’t anchored down well, the epithelium can come off with seemingly trivial trauma. An example is when the eyes first open in the morning. The lid crossing the dry cornea causes a scratch. Another example is with eye rubbing. Erosions usually last several days. However, they can last much longer depending on the size of the abrasion and the underlying health of the cornea.
The second set of symptoms are blurry and double vision. Because the epithelium isn’t anchored down well, folds or ridges may develop on the corneal surface from shifting epithelium. These ridges, called map and fingerprint lines, are visible during the eye exam. A smooth corneal surface is required for clear vision, so these surface irregularities degrade vision.
As the name implies, recurrent corneal erosions can become truly annoying as the cornea tends to heal, and then re-erode weeks, months or even years later. This is always accompanied by pain, light sensitivity and a foriegn body sensation.
What treatments are available?
For recurrent erosions, ointments and bandage contact lenses are often used as first line therapy. We often prescribe the drug doxycycline, as well, because it has been shown to help the cornea heal more quickly.
Depending on the situation, stromal puncture, which is an in-office procedure which allows the epithelium to stick down tighter, can be performed.
For recurrent erosions that don’t respond to the simple therapies, Phototherapeutic Keratectomy (PTK), which utilizes the excimer laser, is very effective at creating a stickier surface for the epithelium.
For blurry or double vision, the most effective therapy is to remove the irregular epithelium (essentially creating a large abrasion) to allowing the epithelium to regrow. The new epithelium is smoother and allows better vision.
What is Phototherpeutic Keratectomy (PTK)?
PTK involves the removal of a small amount of corneal tissue with the excimer laser. This creates a rougher surface for epithelial cells to adhere to, thus decreasing the chance of erosions. The excimer laser is the same laser used for LASIK and PRK. On occasion one can combine PTK with PRK to treat refractive errors at the same time; however, the additional treatment is not covered by insurance.
When undergoing PTK, the epithelium is removed before treatment. During the 4-6 days it takes for the epithelium to regrow, the eye will be uncomfortable. Drops will be given to promote healing and lessen pain, and a bandage contact lens will be placed for comfort during that week. PTK for recurrent erosion is usually successful, but there are expected side effects and possible risks. It will likely change the prescription for glasses (refractive error). The risks of any excimer treatment include infection, glare and haloes, ghosting, delayed healing, decreased vision, and scarring. A small dose of a medicine called mitomycin will be used to decrease the chance of scarring. Second surgeries and long term eye drops may be needed.