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Uveitis refers to inflammation of the uvea, the middle vascular coat of the eye, and is the most common cause of inflammatory eye disease and an important cause of blindness and visual impairment in most communities. The annual incidence of uveitis is between 17 and 52 per 100,000 population,1-5 and the prevalence is 38 to 714 cases per 100,000 population.1,2,4-6 It has been estimated that uveitis accounts for about 10% of the visual handicap in the Western world, and up to 35% of all uveitis patients have been reported to suffer significant visual impairment or legal blindness.7,8 As uveitis often afflicts the young adult population in their most productive years of life, the personal and population burden of this sight threatening disease is significant. Knowledge of the different types and etiology of uveitis in various populations is important in the diagnosis and treatment of inflammatory eye disease. There has been a significant increase in our understanding of the pathogenesis and epidemiology of uveitis in the past decade, and this review will attempt to summarize current understanding of these important features of this common disease.Uveitis may occur at any age, but most commonly afflicts those aged between 20 and 59 years.2,9,10 Uveitis in children aged younger than 16 years is relatively uncommon accounting for only 5% to 10% of cases.11 The annual incidence of uveitis in children was reported to be 4 per 100,000 and the prevalence 28 per 100,000 population in a population-based study in Finland.12 Childhood uveitis is associated with unique diagnostic and management issues, tendency for chronic disease, and high complication rates, with severe visual impairment in up to one-third of all children with uveitis.11,13 As in adult patients, anterior uveitis is the most common anatomic type of uveitis in children in the Western world. In contrast to the clinical associations of uveitis in adults, the most common identified etiology of anterior uveitis in children is juvenile idiopathic arthritis (JIA), accounting for about 30% to 40% of anterior uveitis cases in those younger than 16 years of age, and is by far the most common systemic disease association of childhood uveitis.13,14 Posterior uveitis is the next most common type of uveitis in children, with toxoplasma retinochoroiditis being the most common identified etiology, similar to that seen in uveitis of adults.11Particular forms of uveitis may affect certain age groups more frequently, although this is by no means absolute. Pertinent examples of this predilection of uveitis for certain age groups are: JIA-associated chronic anterior uveitis in children; HLA-B27-associated acute anterior uveitis (AAU) predominantly affecting young adults (mean age of about 35 years)15; birdshot retinochoroidopathy in older adults (mean age of about 50 years)16; and uveitis masquerade syndromes, such as intraocular lymphoma, affecting the older population.Overall, males and females are approximately equally affected by uveitis in most clinical uveitis series.9,10,17,18 However, certain forms of uveitis exhibit variable degrees of gender preponderance. Some of the more clearly established examples of this are: the male preponderance (3:1) of HLA-B27-associated AAU15; the female preponderance (5:1) in chronic anterior uveitis of JIA19; and the lack of any gender preponderance in Fuch's heterochromic iridocyclitis.20Genetic, geographic, social, and environmental factors affect the distribution of the types, clinical associations and causes of uveitis in different populations.