The cornea is the clear, dome-shaped area that covers the front of the eye. Light passes through the cornea before reaching the retina in the back of the eye, and so it must remain clear so light can pass through. Corneal opacities can cause anything from minor irritation to vision problems and even blindness. In fact, corneal problems are the fourth leading cause of blindness (after glaucoma, cataracts, and age-related macular degeneration).
Injury, infection, and certain eye diseases can cause corneal opacities. Here is an overview of the symptoms, causes, and treatment of conditions that affect the cornea.
Corneal Opacity Symptoms
The cornea is formed by strong, tough tissue composed of five different layers, each with a specific function. The cornea protects the eye from dust, germs, UV rays, and other foreign substances. Along with the lens, it bends light rays onto the retina so that images appear in focus. If the corneal shape is excessively steep, flat, or not completely round, it can cause nearsightedness, farsightedness, or astigmatism. These are called refractive errors. Certain types of corneal diseases can change the shape of the cornea.
Depending on the cause, symptoms of corneal damage may include:
- Redness and swelling of the eye tissues and eyelid
- Blurred vision
- Sensitivity to light
- Sensation of something in the eye
- Eye discharge
- Milky or cloudy area on the cornea
- Vision loss
Corneal injuries can occur when a foreign object gets in the eye or from something striking the eye. This can cause cuts or scratches to the cornea. Common causes of cornea injury include:
- Chemical irritation
- An object in the eye, such as sand or dust
- Something striking the eye, such as a tree branch
- Radiation injury from the sun, sun lamps, welding, or sun reflected on snow (snow blindness)
- Complications of contact lens wear
Minor corneal abrasions heal quickly, usually within two days. More serious wounds take longer to heal and can cause irritation, pain, tearing, and redness. Something called a cornea erosion can happen when the abrasion re tears. If the cornea becomes deeply scarred it can cause vision problems. Treatment may include patching the eye, using a temporary contact lens, and prescription eye drops or ointments. If vision problems remain or the cornea becomes permanently damaged, you may need a cornea transplant. This surgery removes the damaged cornea and replaces it with a healthy donor cornea.
Corneal infection, also called keratitis, is relatively rare. Several conditions can cause an infection of the cornea, including:
Conjunctivitis (pinkeye). Bacteria, viruses, or allergies can cause conjunctivitis. The condition usually causes only minor eye irritation. However, if it becomes severe or remains untreated, it can lead to corneal infection.
Herpes zoster (shingles). This infection is caused by the same virus that causes chickenpox. In some people, the infection becomes active again later in life, causing a painful, blistering rash called shingles. Shingles that develop on the face, head, or neck can also affect the cornea. Forty percent of people who get shingles in those areas will develop it on the cornea.
Ocular herpes. Herpes of the eye is caused by the herpes simplex virus, the same virus that causes oral and genital herpes. Ocular herpes develops on the eyelid or surface of the eye and can lead to corneal inflammation. This virus is the most common eye infection that causes blindness in the U.S.
Depending on the cause, treatment for corneal infections may include:
Corneal dystrophies are somewhat rare conditions that cause changes to the cornea. There are more than 20 corneal dystrophies. These eye problems are inherited. If someone in your family has one of these eye conditions, you may be at risk.
Corneal dystrophies usually affect both eyes and can cause vision loss and blindness. Sometimes they cause no symptoms and are only discovered during an eye exam. Here are a few of the more common types of corneal dystrophies:
Fuchs' dystrophy progresses slowly, usually affecting people in their 50s and 60s. The condition damages the endothelial cells in the cornea. Symptoms include swelling and blistering of the cornea, blurred vision, pain, and vision problems. Early on, drops, ointments, and special contact lenses may ease symptoms. At later stages, corneal transplants successfully restore vision.
Map-dot-fingerprint dystrophy causes small gaps between the outer layer and the rest of the cornea, called epithelial erosions. These gaps cause blurred vision, pain, sensitivity to glare and light, and other symptoms that often flare up between ages 40 and 70. Usually the symptoms go away on their own without causing vision loss. Many people don't even know they have map-dot-fingerprint dystrophy. When symptoms occur, treatment may include eye drops and ointments, patching the eye, and removing eroded parts of the cornea.
Keratoconusis a progressive thinning of the cornea that affects 1 in 500 people in the U.S., usually in their teens and 20s, but it can occur in nearly every decade of life. With keratoconus, the cornea becomes thin and bulges outward in a cone shape, like a hernia. The condition can cause moderate to severe blurred vision, multiple images, glare, and halos around objects at night and rob people of the ability to lead a normal life. Often nearsightedness and astigmatism develop from keratoconus.
Other symptoms include swelling and scarring of the cornea. In mild cases most people can manage the condition with eyeglasses or special contact lenses. In early to moderate cases where the patient is still visually successful with glasses or contact lenses, corneal crosslinking, a procedure that uses riboflavin and light to strengthen the cornea, is generally recommended.
The goal is to prevent further worsening of disease. Procedures such as Intacs can help improve vision by partially reversing keratoconus. Corneal transplant, a surgery that replaces the cornea with a cadaver cornea, may be an option after all non surgical measures have been tried. Often hard contact lenses and glasses are required afterwards to improve sight.
Other Conditions That Cause Corneal Opacities
Other eye problems and disorders can also lead to corneal opacity, including:
- Iridocorneal endothelial syndrome, a condition that affects both the iris and cornea, usually only in one eye. It also causes glaucoma, which can be treated with medication.
- Pterygium, a red vascular growth of tissue on the cornea.
- Stevens-Johnson syndrome, a serious skin disorder that also can affect the eyes.
Preventing Corneal Opacities
Although corneal opacities have many causes, there are a few things you can do to help prevent damage to your cornea:
Wear protective eyewear. Protect your eyes with goggles or safety glasses during activities that can cause eye injury. This includes using power tools, chopping wood, or handling chemicals. Also be sure to wear sunglasses when spending time outdoors. Make sure your children also wear sunglasses.
Use contact lenses correctly. Follow your eye doctor's instructions for properly handling, storing, disinfecting, and discarding and replacing soft contact lenses.
Have regular eye exams. Many eye conditions can be detected early, before symptoms develop. Also be sure to see your eye doctor right away if you injure your eye or develop any unusual eye symptoms or vision problems.
Know your family history for eye diseases. Because corneal dystrophies are hereditary, you may be at risk if someone in your family has eye disease.