The eye is highly sensitive, and there are several ways in which it protects itself from damage. The eyelid covers the eye, and tears and fluid protect it from infection. The cornea is the outermost layer of the eye and provides a barrier against dirt, germs, and disease.
Because the cornea is one of the first lines of defense, it can be irritated and become inflamed. This is known as keratitis.
Keratitis and the eye
Keratitis is a painful inflammation of the cornea and can have various causes.
Keratitis is a condition affecting the cornea, which is the transparent outer layer at the front of the eye. The cornea helps the eye to focus so that it can see objects clearly.
Keratitis causes the cornea to become inflamed. This can be very painful, cause problems with vision, and make the eye more sensitive to light.
Keratitis does not have one single cause. There is a range of different types of keratitis, and each type needs different treatment.
Causes and risk factors
Keratitis usually happens because something has irritated the eye, for example, an infection or injury. Certain risk factors make it more likely for keratitis to develop.
Wearing contact lenses is a risk, especially if a person wears them overnight. Failing to keep contact lenses or a contact lens case clean increases the chance of getting keratitis.
A person who has recently had an eye disease or injury might mean that they are more likely to develop the condition. People who have the herpes simplex virus are at risk of developing viral keratitis.
Keratitis can be caused by the eyes drying out. A problem with the eyelids or tear ducts can mean that a person's eye is not as moist as it needs to be.
Fungal keratitis occurs when part of a tree or plant, such as a twig, injures the eye, so those people who work with plants are more at risk.
Exposing the eyes to water — such as when swimming or in a hot tub — is a high risk for keratitis.
A person should always clean their contact lenses with a contact lens solution, not wash them in water.
Keeping contact lenses and lens cases clean will help reduce the risk of developing keratitis.
There are two main types of keratitis: infectious and noninfectious. Within these two categories, there are other forms of the condition.
Noninfectious causes of keratitis include:
- wearing contact lenses for too long
- the eye drying out, sometimes if the eye does not produce enough tears
- an allergy, for example to cosmetics or pollution
- something in the eye that should not be there
- injury to the cornea
- exposure to intense sunlight, for example from water or snow
- vitamin A deficiency
Infectious types of keratitis include:
- bacterial, usually from unclean contact lenses
- fungal, most often from an eye injury by a tree branch or plant
- viral, from infection with the herpes simplex virus or herpes zoster virus
- parasitic, caused by a tiny organism often found in lakes and rivers
The best treatment for keratitis will depend on which type of the condition someone has.
Pain in the eye is the key symptom of keratitis. Because the cornea is the part of the eye that helps to focus sight, vision may be blurred.
Someone may also feel that they have something in their eye, even if they do not, and the eye may water more than usual. The eye can also appear red, and there may be some discharge.
A person with keratitis may be sensitive to light, which is known as photophobia. They may dislike looking toward a light, having a bright light on in the house, or being outside in strong sunlight.
Keratitis can be serious and may cause loss of vision or blindness if left untreated. The condition is usually treatable if diagnosed early enough.
Complications can include permanent scarring, ulcers on the cornea, or less commonly glaucoma. This is a condition where pressure inside the eye can cause problems with vision.
A person should see a doctor or eye doctor if they have symptoms of keratitis.
An eye doctor will examine the eye and ask questions about what may have caused keratitis.
A doctor may diagnose bacterial or fungal keratitis by taking a small scraping from the cornea to send to a laboratory to be tested.
Viral keratitis does not need laboratory testing, but a doctor will ask for information about a person's medical history.
Parasitic keratitis may need a more detailed examination of the eye so that the doctor can see the parasite causing the condition.
Antibacterial eye drops may be prescribed for mild bacterial keratitis.
If a person has keratitis and wears contact lenses, they should take them out as soon as they develop any symptoms of infection or irritation. Contact lenses should not be used again until the condition has gone away.
If a person has is mild bacterial keratitis, a doctor may recommend they use antibacterial eye drops.
People can apply eye drops at home and will need to use them regularly. As the condition improves, individuals can use the medication less often.
People who have fungal keratitis will need to use antifungal medication for some months. If this does not resolve the condition, surgery may be necessary in extreme cases.
Eye drops or antiviral medication are used to treat viral keratitis. As there is no cure for the herpes simplex virus that can cause viral keratitis, the condition can happen again.
Parasitic keratitis is the most difficult type to treat and requires urgent medical treatment as well as surgery.
During treatment, someone should see an eye doctor if:
- the condition is not improving with the use of eye drops
- their sight becomes blurred
- the eye becomes more painful, or redder
- a white spot on the cornea grows in size
Apart from viral keratitis, most people can avoid other forms of the condition by following good contact lens hygiene.
People can help to prevent keratitis by:
- following the advice of their eye doctor about how to wear, replace, store, and clean contact lenses
- washing and drying hands with soap and water before touching the eyes or contact lenses
- avoiding sleeping in contact lenses
- keeping water away from contact lenses, such as when showering or swimming
- cleaning contact lenses with contact lens solution
- visiting an eye doctor regularly, and contacting them with any symptoms that give concern
Keratitis can affect people who do not wear contact lenses. It is important to protect the eyes from damage that can cause the condition.
Steps to protect the eyes include:
- wearing protective eyewear if working with plants or trees
- wearing sunglasses when exposed to bright sunlight
- being aware of anything that can cause an allergy, and avoiding them if possible
- eating a diet that includes vitamin A, which can be found in milk and eggs
It may also be possible to reduce the risk of viral keratitis. People should take care not to touch the eyes or the area around them, and only use eye drops that have been prescribed by a doctor.
Keratitis is treatable, but it is important to stop wearing contact lenses as soon as the eye becomes inflamed.
A person should seek medical advice to find the cause of the condition, as treatment can vary depending on the root of the problem.
Those who wear contact lenses are most at risk of infection. Following advice on cleaning and storing contact lenses should prevent keratitis in most cases.