What is a corneal erosion? What are its symptoms?
The cornea is the clear window in the front of the eye. The outer 10% of the cornea’s thickness is a protective layer called the epithelium. Just like the outer layer of cells on our skin, the corneal epithelium replaces itself often. We get a new corneal epithelium every week!
A corneal abrasion occurs when this top layer, the epithelium, is damaged. This usually occurs from trauma and is commonly caused by getting a foreign body into the eye or scratch by a fingernail. However, an abrasion can also develop in the absence of trauma. This is called “corneal erosion”. In a patient prone to this condition, simply opening the eyes in the morning can rip away an area of the epithelium. Most of us can recall falling and skinning our knees as children. Anyone who has had their cornea scratched can relate that this is far more painful, because the cornea is one of the most sensitive areas of our body. (A single grain of sand touching the cornea hurts: no other area is that sensitive!) If the corneal epithelium is removed, a patient feels severe tearing with burning and foreign body sensation, and a strong urge to close the eye. The eye naturally wants to stay shut until the defect heals. A corneal erosion can heal in just a few hours, often resolving by the time one arrives at the doctor’s office.
What causes corneal erosion?
It is typically a combination of genetic weak adherence and mechanical friction that causes spontaneous erosions of the corneal epithelium.
The weaker the adherence between the epithelium and the underlying corneal layers, the easier it is for the epithelium to be rubbed. The weakness can be genetic or due to trauma. Some people have epithelial corneal dystrophies or other genetic conditions where they are born with more weakly adherent epithelium that is prone to spontaneous erosions. The most common of these is the epithelial basement membrane (map-dot-fingerprint) dystrophy. Some patients after experiencing a traumatic abrasion have difficulty healing the epithelium with firm attachment. It the epithelium does not heal right the first time, it may remain weak at that location and be prone to recurrent erosions that prevent the area from ever healing strongly.
The more friction there is on the epithelium, the more likely it is to erode. A fingernail digging into a cornea is considered maximum friction, and can even abrade strongly adherent epithelium. But friction is also elevated in a dry eye. Think of a windshield wiper going across a dry windshield: instead of gliding you can even hear its friction. When the eye surface is dry, its mucous coating becomes sticky as opposed to slippery. The friction between such sticky dry surfaces, is often enough to rip and rub off some epithelium… especially in conditions with weak adherence. Our eyes are often the stickiest in the morning which is why spontaneous erosions commonly happen when first opening the eyes upon awakening.
What are the complications of corneal erosion?
For the most part, corneal erosions are problematic because of the prominent pain and distress they cause the patient. The unpredictable nature of this condition can lead to much anxiety and missed days of work. Rarely, erosions can cause vision loss from corneal infection or scarring.
How are corneal erosions treated?
Medical therapies are often tried first. Surgical therapies are reserved for more severe cases.
We try to reduce corneal friction by lubricating it. Dry eye syndrome can be treated with artificial tears during the day and thick lubricants, such as Refresh PM Ointment, at night. Because the bedtime ointment is not likely to last until morning, we often ask patients to wake and reapply it in the middle of the night. View our section on dry eye syndrome to see other ways we can treat dry eye to help corneal erosions.
A bandage contact lens reduces friction on the cornea because it blocks the eyelids from directly rubbing against it. The contact can be left in place day and night for a month or so. We change the contact from time to time if we believe a longer treatment course would be helpful. The goal is to attain 3-6 months without an erosion which will make recurrences less likely. A daily antibiotic is necessary to prevent infection when a bandage contact lens is in place. Once a patient has gone 3-6 months without an erosion, the contact can be removed and concentrated salt drops (Muro 128) can be taken 3 times a day to help further strengthen the epithelium. We may sometimes try Muro 128 without a contact lens.
Patients who fail or are likely to fail medical therapy are offered superficial keratectomy (SK) or phototherapeutic keratectomy (PTK). These procedures remove the epithelium so that more normal and stronger epithelium can heal in. A bandage contact lens is used to protect the eye surface for 3-6 months after a SK or PTK being done for recurrent corneal erosions.