The cornea, the clear front part of the eye through which light passes, is subject to many infections and to injury from exposure and from foreign objects. Infection and injury cause inflammation of the cornea--a condition called keratitis. Tissue loss because of inflammation produces an ulcer. The ulcer can either be centrally located, thus greatly affecting vision, or peripherallylocated. There are about 30,000 cases of bacterial corneal ulcers in the United States each year.
A corneal abrasion is basically a superficial cut or scrape on the cornea. Acorneal abrasion is not as serious as a corneal ulcer, which is generally deeper and more severe than an abrasion.
The most common cause of corneal ulcers is germs, but most of them cannot invade a healthy cornea with adequate tears and a functioning eyelid. They gainaccess because injury has impaired these defense mechanisms. A direct injuryfrom a foreign object inoculates germs directly through the outer layer of the cornea, just as it does to the skin. A caustic chemical can inflame the cornea by itself or so damage it that germs can invade. Improper use of contactlenses has become a common cause of corneal injury. Eyelid or tear function failure is the other way to make the eye vulnerable to infection. Tears and the eyelid together wash the eye and prevent foreign material from settling in.Tears contain enzymes and other substances to help protect against infection. Certain diseases dry up tear production, leaving the cornea dry and defenseless. Other diseases paralyze or weaken the eyelids so that they cannot effectively protect and cleanse the eyes.
A corneal abrasion is usually the result of direct injury to the eye, often from a fingernail scratch, makeup brushes, contact lenses, foreign body, or even twigs. Patients often complain of feeling a foreign body in their eye, andthey may have pain, sensitivity to light, or tearing.
Viruses, bacteria, fungi, and a protozoan called Acanthamoeba can allinvade the cornea and damage it under suitable conditions.
- Bacteria from a common conjunctivitis (pink eye) rarely spread to the cornea, but can ifuntreated.
- Fecal bacteria are more likely to be able to infect thecornea.
- A bacterium called Pseudomonas aeruginosa, which cancontaminate eyedrops, is particularly able to cause corneal infection.
- A group of incomplete bacteria known as Chlamydia can be transmitted to the eye directly by flies or dirty hands. One form of chlamydial infection is the leading cause of blindness in developing countries and is known asEgyptian ophthalmia or trachoma. Another type of Chlamydia causes a sexually transmitted disease.
- Other sexually transmitted diseases--forexample, syphilis--can affect the cornea.
The most common viruses to damage the cornea are adenoviruses and herpes viruses. Viral and fungal infections are often caused by improper use of topicalcorticosteroids. If topical corticosteroids are used in a patient with Herpessimplex keratitis, the ulcer can get much worse and blindness could result.
Symptoms are obvious. The cornea is intensely sensitive, so corneal ulcers normally produce severe pain. If the corneal ulcer is centrally located, visionis impaired or completely absent. Tearing is present and the eye is red. Ithurts to look at bright lights.
The doctor will take a case history to try to determine the cause of the ulcer. This can include improper use of contact lenses; injury, such as a scratchfrom a twig; or severe dry eye. An instrument called a slit lamp will be used to examine the cornea. The slit lamp is a microscope with a light source that magnifies the cornea, allowing the extent of the ulcer to be seen. Fluorescein, a yellow dye, may be used to illuminate further detail. If a germ is responsible for the ulcer, identification may require scraping samples directlyfrom the cornea, conjunctiva, and lids, and sending them to the laboratory.
Ophthalmologists and optometrists, who treat eye disorders, are well qualified to diagnose corneal abrasions. The doctor will check the patient's vision (visual acuity) in both eyes with an eye chart. A patient history will also betaken, which may help to determine the cause of the abrasion. A slit lamp, which is basically a microscope and light source, will allow the doctor to seethe abrasion. Fluorescein, a yellow dye, may be placed into the eye to determine the extent of the abrasion. The fluorescein will temporarily stain the affected area.
A corneal ulcer needs to be treated aggressively, as it can result in loss ofvision. The first step is to eliminate infection. Broad spectrum antibioticswill be used before the lab results come back. Medications may then be changed to more specifically target the cause of the infection. A combination of medications may be necessary. Patients should return for their follow-up visits, so that the doctor can monitor the healing process. The cornea can heal from many insults, but if it remains scarred, corneal transplantation may be necessary to restore vision. If the corneal ulcer is large, hospitalization maybe necessary.
The cornea has a remarkable ability to heal itself, so treatment is designedto minimize complications. If an abrasion is very small, the doctor might just suggest an eye lubricant and a follow-up visit the next day. A very small abrasion should heal in 1-2 days; others usually in one week. However, to avoid a possible infection, an antibiotic eye drop may be prescribed. Sometimes additional eye drops may make the eye feel more comfortable. Depending upon the extent of the abrasion, some doctors may patch the affected eye. It is veryimportant to go for the follow-up checkup to make sure an infection does notoccur. Use of contact lenses should not be resumed without the doctor's approval.
Treated early enough, corneal infections will usually resolve, perhaps even without the formation of an ulcer. However, left untreated, infections can lead to ulcers and the corneal ulcer can result in scarring or perforation of the cornea. Other problems may occur as well, including glaucoma. Patients withcertain systemic diseases that impede healing (such as diabetes mellitus orrheumatoid arthritis) may need more aggressive treatment. The later the treatment, the more damage will be done and the more scarring will result. Cornealtransplant is standard treatment with a high probability of success.
In typical abrasion cases, the prognosis is good. The cornea will heal itself, usually within several days. A very deep abrasion may lead to scarring. Ifthe abrasion does not heal properly, a recurrent corneal erosion (RCE) may result months or even years later. The symptoms are the same as for an abrasion(e.g., tearing, foreign body sensation, and blurred vision), but it will keep occurring. Similar or additional treatment for the RCE may be necessary.
Attentive care of contact lenses will greatly reduce the incidence of cornealdamage and ulceration. Germs that cause no problems in the mouth or on the hands can damage the eye, so contact lens wearers must wash their hands beforetouching their lenses and must not use saliva to moisten them. Tap water should not be used to rinse the lenses. Contacts should be removed whenever there is irritation and left out until the eyes are back to normal. It is not advisable to wear contact lenses while swimming or in hot tubs. Daily wear contact lenses have been found to be less of a risk than contacts for overnight wear (extended wear). Organisms have been cultured from contact lens cases, sothe cases should be rinsed in hot water and allowed to air dry. Cases shouldbe replaced every three months. Patients should follow their doctors' schedules for replacement of the contacts.
Eye protection in the workplace, or wherever tiny particles are flying around, is essential. Ultraviolet (UV) coatings on glasses or sunglasses can help protect the eyes from the sun's rays. Goggles with UV protection should be worn when skiing or in suntanning salons, to protect against UV rays. Prompt attention to any red eye should prevent progressive damage.
For people with inadequate tears, use of artificial tears eyedrops will prevent damage from drying. Eyelids that do not close adequately may temporarily have to be sewn shut to protect the eye until more lasting treatment can be instituted.