Cornea and Corneal Disease

What is the cornea?
The cornea is the eye’s outermost layer. It is the clear, dome­shaped surface that covers the front of the eye. It plays an important role in focusing your vision.
 
 
Why are tears important to the cornea?
Every time we blink, tears are distributed across the cornea to keep the eye moist, help wounds heal, and protect against infection. Tears form in 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 the conjunctiva – the mucous membrane that covers the front of the eye and the inside of the eyelids;
A bottom (mucin) layer that helps spread the aqueous layer across the eye to ensure that the eye remains wet.
 
 
What does the cornea do?
 
The cornea acts as a barrier against dirt, germs, and other particles that can harm the eye. The cornea shares this protective task with the eyelids and eye sockets, tears, and the sclera (white part of the eye). The cornea also plays a key role in vision by helping focus the light that comes into the eye. The cornea is responsible for 65­-75 percent of the eye’s total focusing power.
 
The cornea and lens of the eye are built to focus light on the retina, which is the light-sensitive tissue at the back of the eye. When light strikes the cornea, it bends—or refracts—the incoming light onto the lens. The lens refocuses that light onto the retina, which starts the translation of light into vision. The retina converts light into electrical impulses that travel through the optic nerve to the brain, which interprets them as images.
 
The refractive process the eye uses is similar to the way a camera takes a picture. The cornea and lens in the eye act as the camera lens. The retina is like the film (in older cameras), or the image sensor (in digital cameras). If the image is not focused properly, the retina makes a blurry image.
 
The cornea also serves as a filter that screens out damaging ultraviolet (UV) light from the sun. Without this protection, the lens and the retina would be exposed to injury from UV rays.
 
What are some common conditions that affect the cornea?
 
Injuries
 
After minor injuries or scratches, the cornea usually heals on its own. Deeper injuries can cause corneal scarring, resulting in a haze on the cornea that impairs vision. If you have a deep injury, or a corneal disease or disorder, you could experience:
 
Pain in the eye
Sensitivity to light
Reduced vision or blurry vision
Redness or inflammation in the eye
Headache, nausea, fatigue
If you experience any of these symptoms, seek help from an eye care professional.
 
Allergies
 
The most common allergies that affect the eye are those related to pollen, particularly when the weather is warm and dry. Symptoms in the eye include redness, itching, tearing, burning, stinging, and watery discharge, although usually not severe enough to require medical attention. Antihistamine decongestant eyedrops effectively reduce these symptoms. Rain and cooler weather, which decreases the amount of pollen in the air, can also provide relief. For more information see Facts about Pink Eye (Conjunctivitis).
 
Keratitis
 
Keratitis is an inflammation of the cornea. Noninfectious keratitis can be caused by a minor injury, or from wearing contact lenses too long. Infection is the most common cause of keratitis. Infectious keratitis can be caused by bacteria, viruses, fungi or parasites. Often, these infections are also related to contact lens wear, especially improper cleaning of contact lenses or overuse of old contact lenses that should be discarded. Minor corneal infections are usually treated with antibacterial eye drops. If the problem is severe, it may require more intensive antibiotic or antifungal treatment to eliminate the infection, as well as steroid eye drops to reduce inflammation.
 
Dry eye
 
Dry eye is a condition in which the eye produces fewer or lower quality tears and is unable to keep its surface lubricated.
 
The main symptom of dry eye is usually a scratchy feeling or as if something is in your eye. Other symptoms include stinging or burning in the eye, episodes of excess tearing that follow periods of dryness, discharge from the eye, and pain and redness in the eye.
 

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