What is the Cornea?
The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye to shield the rest of the eye from germs, dust, and other harmful matter. The cornea functions like a window that controls and focuses light entering the eye. To see well, all five layers of the cornea must be free of any cloudy or opaque areas.
What are some common cornea conditions?
Click below to learn about some of the most common cornea diseases and conditions we diagnose and treat at San Antonio Eye Center. Don’t see the information you are looking for here? We welcome you to contact us to ask questions about your eye health.
Allergies affecting the eye are fairly common. The most common allergies are those related to pollen, particularly when the weather is warm and dry. Other allergy sources include medications, contact lens wear, animal hair, makeup, face cream, and soaps.
Symptoms are temporary and may include redness, itching, tearing, burning, stinging, and watery discharge. These symptoms may be eliminated by avoiding contact with these sources.
Conjunctivitis (Pink Eye)
This term describes a group of diseases that cause swelling, itching, burning, and redness of the conjunctiva. The conjunctive is the protective membrane that lines the eyelids and covers exposed areas of the sclera, or white of the eye. Conjunctivitis is contagious can be caused by a bacterial or viral infection, allergy, environmental irritants, a contact lens product, eyedrops, or eye ointments.
At its onset, conjunctivitis is usually painless and does not harm vision. The infection will clear in most cases without medical care. In some cases, treatment will be needed. If treatment is delayed, the infection may worsen and cause inflammation and vision loss.
Sometimes the cornea is damaged after a foreign object has entered the tissue, such as from a poke in the eye. At other times, bacteria or fungi from a contaminated contact lens can pass into the cornea. Situations like these can cause painful inflammation and corneal infections. Corneal infections can reduce visual clarity, produce corneal discharges, erode the cornea, or lead to corneal scarring which can impair vision and may require a corneal transplant.
The deeper the corneal infection, the more severe the symptoms and complications. These infections, although relatively infrequent, are the most serious complication of contact lens wear.
Minor corneal infections are commonly treated with eye drops. Severe problems may require more intensive antibiotic or anti-fungal treatment, as well as steroid eye drops to reduce inflammation. Frequent visits to an eye care professional may be necessary for several months to eliminate the problem.
The continuous production and drainage of tears is important to the eye’s health. Tears keep the eye moist, help wounds heal, and protect against eye infection. In people with dry eye, the eye produces fewer or poor quality tears and is unable to keep its surface lubricated and comfortable.
The tear film consists of three layers–an outer, oily (lipid) layer that keeps tears from evaporating too quickly and helps tears remain on the eye; a middle (aqueous) layer that nourishes the cornea and conjunctiva; and a bottom (mucin) layer that helps to spread the aqueous layer across the eye to ensure that the eye remains wet. As we age, the eyes usually produce fewer tears. In some cases, the lipid and mucin layers produced by the eye are of such poor quality that tears cannot remain onthe eye long enough to keep the eye sufficiently lubricated.
Dry eye symptoms include:
- Scratchy or sandy feeling as if something is in the eye
- Stinging or burning
- Excessive tearing that follow periods of very dry sensation
- A stringy discharge from the eye
- Pain and redness of the eye
- Heaviness of the eyelids
- Blurred, changing, or decreased vision (although loss of vision is uncommon)
Dry eye is more common in women, especially after menopause. Dry eye can occur in climates with dry air, as well as with the use of some drugs, including antihistamines, nasal decongestants, tranquilizers, and anti-depressant drugs. People with dry eye should let their health care providers know all the medications they are taking, since some of them may intensify dry eye symptoms.
People with connective tissue diseases, such as rheumatoid arthritis, can also develop dry eye. It is important to note that dry eye is sometimes a symptom of Sjögren’s syndrome, a disease that attacks the body’s lubricating glands, such as the tear and salivary glands. A complete physical examination may diagnose any underlying diseases.
Artificial tears, which lubricate the eye, are the principal treatment for dry eye. They are available over-the-counter as eye drops. Sterile ointments are sometimes used at night to help prevent the eye from drying. Using humidifiers, wearing wrap-around glasses when outside, and avoiding windy and dry conditions may bring relief. For people with severe cases of dry eye, temporary or permanent closure of the tear drain (small openings at the inner corner of the eyelids where tears drain from the eye) may be helpful.
Fuchs’ dystrophy is a slowly progressing disease that usually affects both eyes and is slightly more common in women. Although doctors can often see early signs of Fuchs’ dystrophy in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s.
Fuchs’ dystrophy occurs when endothelial cells (single layer of cells on the inner surface of the cornea) gradually deteriorate. As more endothelial cells are lost over the years, the cornea may swell, become painful, and severely distort vision.
At first, a person with Fuchs’ dystrophy will awaken with blurred vision that will gradually clear during the day. This occurs because the cornea is normally thicker in the morning; it retains fluids during sleep that evaporate in the tear film while we are awake. As the disease worsens, this swelling will remain constant and reduce vision throughout the day.
Treatment & Cornea Transplants
When treating the disease, doctors will try first to reduce the swelling with drops, ointments, or soft contact lenses. They also may instruct a person to use a hair dryer, held at arm’s length or directed across the face, to dry out blisters that may form on the front of the cornea. This can be done two or three times a day.
When the disease interferes with daily activities, a person may need to consider having a corneal transplant to restore sight. The short-term success rate of corneal transplantation is quite good for people with Fuchs’ dystrophy. However, some studies suggest that the long-term survival of the new cornea can be a problem.
Learn more about cornea transplants.
Herpes Zoster (Shingles)
This infection is produced by the varicella-zoster virus, the same virus that causes chickenpox. After an initial outbreak of chickenpox (often during childhood), the virus remains inactive within the nerve cells of the central nervous system. In some people, the varicella-zoster virus will reactivate at another time in their lives.
When this occurs, the virus travels down long nerve fibers and infects some part of the body, producing a blistering rash (shingles), fever, painful inflammations of the affected nerve fibers, and a general feeling of sluggishness.
Varicella-zoster virus may travel to the head and neck, perhaps involving an eye, part of the nose, cheek, and forehead. In about 40 percent of those with shingles in these areas, the virus infects the cornea. Doctors will often prescribe oral anti-viral treatment to reduce the risk of the virus infecting cells deep within the tissue, which could inflame and scar the cornea. The disease may also cause decreased corneal sensitivity, meaning that foreign matter, such as eyelashes, in the eye are not felt as keenly. For many, this decreased sensitivity will be permanent.
Although shingles can occur in anyone exposed to the varicella-zoster virus, research has established two general risk factors for the disease: (1) advanced age; and (2) a weakened immune system.
Unlike herpes simplex I, the varicella-zoster virus does not usually flare up more than once in adults with normally functioning immune systems. Be aware that corneal problems may arise months after the shingles are gone. For this reason, it is important that people who have had facial shingles schedule follow-up eye examinations.
Iridocorneal Endothelial Syndrome
More common in women and usually diagnosed between ages 30-50, iridocorneal endothelial (ICE) syndrome has three main features: (1) visible changes in the iris, the colored part of the eye that regulates the amount of light entering the eye; (2) swelling of the cornea; and (3) the development of glaucoma, a disease that can cause severe vision loss when normal fluid inside the eye cannot drain properly. ICE is usually present in only one eye.
ICE syndrome is actually a grouping of three closely linked conditions: iris nevus (or Cogan-Reese) syndrome; Chandler’s syndrome; and essential (progressive) iris atrophy (hence the acronym ICE). The most common feature of this group of diseases is the movement of endothelial cells off the cornea onto the iris.
The cause of this disease is unknown. While we do not yet know how to keep ICE syndrome from progressing, the glaucoma associated with the disease can be treated with medication, and a corneal transplant can treat the corneal swelling.
This disorder is a progressive thinning of the cornea and is the most common corneal dystrophy in the U.S. Keratoconus affects one in every 2,000 Americans. It is more prevalent in teenagers and adults in their 20s. Keratoconus arises when the middle of the cornea thins and gradually bulges outward, forming a rounded cone shape.
This abnormal curvature changes the cornea’s refractive power, producing moderate to severe distortion (astigmatism) and blurriness (nearsightedness) of vision. Keratoconus may also cause swelling and a sight-impairing scarring of the tissue.
Studies indicate that keratoconus stems from one of several possible causes:
- An inherited corneal abnormality. About seven percent of those with the condition have a family history of keratoconus.
- An eye injury, i.e., excessive eye rubbing or wearing hard contact lenses for many years.
- Certain eye diseases, such as retinitis pigmentosa, retinopathy of prematurity, and vernal keratoconjunctivitis.
- Systemic diseases, such as Leber’s congenital amaurosis, Ehlers-Danlos syndrome, Down syndrome, and osteogenesis imperfecta.
Keratoconus usually affects both eyes. At first, people can correct their vision with eyeglasses. But as the astigmatism worsens, they must rely on specially fitted contact lenses to reduce the distortion and provide better vision. Although finding a comfortable contact lens can be an extremely frustrating and difficult process, it is crucial because a poorly fitting lens could further damage the cornea and make wearing a contact lens intolerable.
In most cases, the cornea will stabilize after a few years without ever causing severe vision problems. But in about 10 to 20 percent of people with keratoconus, the cornea will eventually become too scarred or will not tolerate a contact lens. If either of these problems occur, a corneal transplant may be needed. This operation is successful in more than 90 percent of those with advanced keratoconus. Several studies have also reported that 80 percent or more of these patients have 20/40 vision or better after the operation.
Lattice dystrophy gets its name from an accumulation of abnormal protein fibers throughout the middle and anterior stroma (the thickest layer of the cornea). During an eye examination, the doctor sees these deposits in the stroma as clear, comma-shaped overlapping dots and branching filaments, creating a lattice effect.
Over time, the lattice lines will grow opaque and involve more of the stroma. They will also gradually converge, giving the cornea a cloudiness that may also reduce vision.
In some people, these abnormal protein fibers can accumulate under the cornea’s outer layer–the epithelium. This can cause erosion of the epithelium. This condition is known as recurrent epithelial erosion. These erosions: (1) alter the cornea’s normal curvature, resulting in temporary vision problems; and (2) expose the nerves that line the cornea, causing severe pain. Even the involuntary act of blinking can be painful.
To ease this pain, a doctor may prescribe eye drops and ointments to reduce the friction on the eroded cornea. In some cases, an eye patch may be used to immobilize the eyelids. With effective care, these erosions usually heal within three days, although occasional sensations of pain may occur for the next six to eight weeks.
By about age 40, some people with lattice dystrophy will have scarring under the epithelium, resulting in a haze on the cornea that can greatly obscure vision. In this case, a corneal transplant may be needed. Although people with lattice dystrophy have an excellent chance for a successful transplant, the disease may also arise in the donor cornea in as little as three years. In one study, about half of the transplant patients with lattice dystrophy had a recurrence of the disease from between two to 26 years after the operation. Of these, 15 percent required a second corneal transplant. Early lattice and recurrent lattice arising in the donor cornea responds well to treatment with the excimer laser.
Although lattice dystrophy can occur at any time in life, the condition usually arises in children between the ages of two and seven.
This dystrophy occurs when the basement membrane develops abnormally the front layer of the cornea (epithelium) basement membrane develops abnormally (the basement membrane serves as the foundation on which the epithelial cells, which absorb nutrients from tears, anchor and organize themselves). When the basement membrane develops abnormally, the epithelial cells cannot properly adhere to it. This, in turn, causes recurrent epithelial erosions, in which the epithelium’s outermost layer rises slightly, exposing a small gap between the outermost layer and the rest of the cornea.
Map-dot-fingerprint dystrophy, which tends to occur in both eyes, usually affects adults between the ages of 40 and 70, although it can develop earlier in life.
Epithelial erosions can be a chronic problem. They may alter the cornea’s normal curvature, causing periodic blurred vision. They may also expose the nerve endings that line the tissue, resulting in moderate to severe pain lasting as long as several days. Generally, the pain will be worse on awakening in the morning. Other symptoms include sensitivity to light, excessive tearing, and foreign body sensation in the eye.
Typically, map-dot-fingerprint dystrophy will flare up occasionally for a few years and then go away on its own, with no lasting loss of vision. Most people never know that they have map-dot-fingerprint dystrophy, since they do not have any pain or vision loss. However, if treatment is needed, doctors will try to control the pain associated with the epithelial erosions. They may patch the eye to immobilize it, or prescribe lubricating eye drops and ointments. With treatment, these erosions usually heal within three days, although periodic flashes of pain may occur for several weeks thereafter. Other treatments include anterior corneal punctures to allow better adherence of cells; corneal scraping to remove eroded areas of the cornea and allow regeneration of healthy epithelial tissue; and use of the excimer laser to remove surface irregularities.
Herpes of the eye, or ocular herpes, is a recurrent viral infection that is caused by the herpes simplex virus and is the most common infectious cause of corneal blindness in the U.S. Previous studies show that once people develop ocular herpes, they have up to a 50 percent chance of having a recurrence. This second flare-up could come weeks or even years after the initial occurrence.
Ocular herpes can produce a painful sore on the eyelid or surface of the eye and cause inflammation of the cornea.
Prompt treatment with anti-viral drugs helps to stop the herpes virus from multiplying and destroying epithelial cells. However, the infection may spread deeper into the cornea and develop into a more severe infection called stromal keratitis, which causes the body’s immune system to attack and destroy stromal cells. Stromal keratitis is more difficult to treat than less severe ocular herpes infections. Recurrent episodes of stromal keratitis can cause scarring of the cornea, which can lead to loss of vision and possibly blindness.
Like other herpetic infections, herpes of the eye can be controlled. An estimated 400,000 Americans have had some form of ocular herpes. Each year, nearly 50,000 new and recurring cases are diagnosed in the United States, with the more serious stromal keratitis accounting for about 25 percent. In one large study, researchers found that recurrence rate of ocular herpes was 10 percent within one year, 23 percent within two years, and 63 percent within 20 years. Some factors believed to be associated with recurrence include fever, stress, sunlight, and eye injury.
A pterygium is a pinkish, triangular-shaped tissue growth on the cornea. Some pterygia grow slowly throughout a person’s life, while others stop growing after a certain point. A pterygium rarely grows so large that it begins to cover the pupil of the eye.
Pterygia are more common in sunny climates and in the 20-40 age group. Scientists do not know what causes pterygia to develop. However, since people who have pterygia usually have spent a significant time outdoors, many doctors believe ultraviolet (UV) light from the sun may be a factor. In areas where sunlight is strong, wearing protective eyeglasses, sunglasses, and/or hats with brims are suggested. While some studies report a higher prevalence of pterygia in men than in women, this may reflect different rates of exposure to UV light.
Because a pterygium is visible, many people want to have it removed for cosmetic reasons. It is usually not too noticeable unless it becomes red and swollen from dust or air pollutants. Surgery to remove a pterygium is not recommended unless it affects vision. If a pterygium is surgically removed, it may grow back, particularly if the patient is less than 40 years of age. Lubricants can reduce the redness and provide relief from the chronic irritation.
About 120 million people in the United States wear eyeglasses or contact lenses to correct nearsightedness, farsightedness, or astigmatism. These vision disorders–called refractive errors– affect the cornea and are the most common of all vision problems in this country. Refractive errors are usually corrected by eyeglasses or contact lenses. Although eyeglasses or contact lenses are safe and effective methods for treating refractive errors, refractive surgeries, such as LASIK, are becoming an increasingly popular option.
Stevens-Johnson Syndrome (SJS), also called erythema multiforme major, is a disorder of the skin that can also affect the eyes.
SJS is characterized by painful, blistery lesions on the skin and the mucous membranes (the thin, moist tissues that line body cavities) of the mouth, throat, genital region, and eyelids. SJS can cause serious eye problems, such as severe conjunctivitis; iritis, an inflammation inside the eye; corneal blisters and erosions; and corneal holes. In some cases, the ocular complications from SJS can be disabling and lead to severe vision loss.
Scientists are not certain why SJS develops. The most commonly cited cause of SJS is an adverse allergic drug reaction. Almost any drug–but most particularly sulfa drugs–can cause SJS. The allergic reaction to the drug may not occur until 7-14 days after first using it. SJS can also be preceded by a viral infection, such as herpes or the mumps, and its accompanying fever, sore throat, and sluggishness.
Treatment for the eye may include artificial tears, antibiotics, or corticosteroids. About one-third of all patients diagnosed with SJS have recurrences of the disease.
SJS occurs twice as often in men as women, and most cases appear in children and young adults under 30, although it can develop in people at any age.
A corneal abrasion is an injury (scratch or cut) to the front of the cornea. Abrasions are commonly caused by fingernails scraches, paper cuts, makeup brushes, scrapes from tree or bush limbs, and rubbing the eye. Some eye conditions, such as dry eye, increase the chance of an abrasion.
- The feeling of having something in your eye
- Eye pain and soreness
- Eye redness
- Sensitivity to light
- Blurred vision
Treatment may include the following:
- Patching the injured eye to prevent eyelid blinking from irritating the injury
- Applying lubricating eyedrops or ointment to the eye to form a soothing layer between the eyelid and the abrasion
- Using antibiotics to prevent infection
- Dilating (widening) the pupil to relieve pain
- Wearing a special contact lens to help healing
Minor abrasions usually heal within a day or two, while larger abrasions usually take about a week. It is important not to rub the eye while it is healing. Do not wear your usual contact lenses while it is healing. Ask your ophthalmologist when you may start wearing them again.