Uveitis is inflammation of the uvea, the middle layer of your eye. The eye is shaped much like a tennis ball, with three different layers of tissue surrounding a central gel-filled cavity. The innermost layer is the retina, which senses light and helps to send images to your brain. The middle layer between the sclera and retina is called the uvea. The outermost layer is the sclera, the strong white wall of the eye.

The uvea contains many blood vessels, the veins and arteries that carry blood flow to the eye. Since it nourishes many important parts of the eye (such as the retina), inflammation of the uvea can damage your sight.

Symptoms:
Symptoms of uveitis include:

• Light sensitivity
  
• Blurring of Vision
• Pain
  
• Redness of the eye

Uveitis may come on suddenly with redness and pain, or sometimes with a painless blurring of your vision. A case of simple "red eye" may in fact be a serious problem of uveitis. If your eye becomes red or painful, and doesn't clear up quickly, you should be examined and treated by a medical eye doctor.

Causes:
Uveitis has many different causes:

• A virus, such as shingles, mumps, or herpes
  
• A fungus, such as histoplasmosis
  
• A parasite, such as toxoplasmosis
  
• Related disease in other parts of the body, such as arthritis
  
• A result of injury to the eye. Inflammation in one eye can result from a severe injury to the opposite eye (sympathetic uveitis)
  
• Bacteria, such as syphilis

In most cases of uveitis, the cause remains unknown.

Diagnosis:
A careful eye examination by an ophthalmologist is extremely important when symptoms occur. Inflammation inside the eye can permanently affect sight or even lead to blindness if not treated.

In addition to examining the back of the eye, your ophthalmologist may order blood tests, skin tests, or x-rays to help make a diagnosis. Since uveitis can be associated with disease in the rest of the body, your ophthalmologist will want to know about your overall health and may want to consult your primary care physician.

Are There Different Kinds of Uveitis?
There are different types of uveitis, depending on which part of the eye is affected:

• When the uvea is inflamed near the front of the eye in the iris, it is called iritis. Iritis has a sudden onset and may last six to eight weeks.
  
• If the uvea is inflamed in the middle of the eye, it is called cyclitis. Cyclitis affects the muscle that focuses the lens. Cyclitis can also come on suddenly and last for several months.
  
• An inflammation in the back of the eye is called choroiditis. Choroiditis is slower to begin and may last longer.

Reference: American Academy of Ophthalmology