Uveitis () is the inflammation of the uvea, the pigmented layer that lies between the inner retina and the outer fibrous layer composed of the sclera and cornea. The uvea consists of the middle layer of pigmented vascular structures of the eye and includes the iris, ciliary body, and choroid. Uveitis is described anatomically, by the part of the eye affected, as anterior, intermediate or posterior, from front to back. In the panuveitic form, all parts are involved. The most common form is the anterior one. Symptoms include pain, floaters and blurred vision, and clinical examination may show redness and an irregular pupil, while ophthalmic examination shows dilated ciliary blood vessels and the presence of cells in the anterior chamber. Uveitis may arise spontaneously and associated with some genetic factors, or be associated with a wide range of conditions including autoimmune disease and infections. While the eye is a relatively protected environment, its immune mechanisms may be overcome resulting in inflammation and tissue destruction associated with T-cell activation. The incidence is approximately 1:4500, most commonly between the ages of 20–60. Uveitis is an ophthalmic emergency and requires a thorough examination by an ophthalmologist or optometrist, including dilation of the pupil to allow better visualisation. Urgent treatment is required to control the inflammation. Further procedures may be required to identify any underlying disease. Treatment usually involves the use of steroids, most commonly as eye drops. Any underlying disease, for instance herpes zoster (shingles) will also require treatment.
It is most commonly associated with HLA-B27, which has important features: HLA-B27 AAU can be associated with ocular inflammation alone or in association with systemic disease. HLA-B27 AAU has characteristic clinical features including male preponderance, unilateral alternating acute onset, a non-granulomatous appearance, and frequent recurrences, whereas HLA-B27 negative AAU has an equivalent male to female onset, bilateral chronic course, and more frequent granulomatous appearance. Rheumatoid arthritis is not uncommon in Asian countries as a significant association of uveitis. Noninfectious or autoimmune causes
Sympathetic ophthalmia
Behçet disease
Crohns disease
Fuchs heterochromic iridocyclitis
Granulomatosis with polyangiitis
HLA-B27 related uveitis
Spondyloarthritis (especially seen in ankylosing spondylitis)
Juvenile idiopathic arthritis
Sarcoidosis
Tubulointerstitial nephritis and uveitis syndrome

Infectious causes
Uveitis may be an immune response to fight an infection inside the eye. While representing the minority of patients with uveitis, such possible infections include:

brucellosis
herpesviruses (herpes zoster ophthalmicus - shingles of the eye)
leptospirosis
Lyme disease
presumed ocular histoplasmosis syndrome
syphilis
toxocariasis
toxoplasmic chorioretinitis
tuberculosis
Zika fever

Associated with systemic diseases
Systemic disorders that can be associated with uveitis include:
Enthesitis
Ankylosing spondylitis
Juvenile rheumatoid arthritis
psoriatic arthritis
reactive arthritis
Behçets disease
inflammatory bowel disease
Whipples disease
systemic lupus erythematosus
polyarteritis nodosa
Kawasakis disease
chronic granulomatous disease
sarcoidosis
multiple sclerosis
Vogt–Koyanagi–Harada disease

Drug related side effects
Rifabutin, a derivative of Rifampin, has been shown to cause uveitis. Several reports suggest the use of quinolones, especially Moxifloxacin, may lead to uveitis. White Dot syndromes
Occasionally, uveitis is not associated with a systemic condition: the inflammation is confined to the eye and has unknown cause.