Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Synonyms and keywords:Pars planitis; chronic cyclitis; peripheral uveitis; peripheral cyclitis; peripheral vitreitis; multiple sclerosis; MS; sarcoidosis
Intermediate uveitis refers to inflammation localized to the vitreous and peripheral retina. Primary sites of inflammation include the vitreous of which other such entities as pars planitis, posterior cyclitis, and hyalitis are encompassed. Intermediate uveitis may either be idiopathic or associated with the development of a systemic disease such as multiple sclerosis (MS) or sarcoidosis. As such, intermediate uveitis may be the first expression of a systemic condition. Evidence of a systemic disorder can be found in up to one third of patients with intermediate uveitis. There appears to be a relatively high correlation between intermediate uveitis and the occurrence of MS.
Pars planitis is considered a subset of intermediate uveitis and is characterized by the presence of white exudates (snowbanks) over the pars plana and ora serrata or by aggregates of inflammatory cells in the vitreous (snowballs) in the absence of an infectious etiology (eg, Lyme disease) or a systemic disease (eg, sarcoidosis). Some authorities believe that patients with pars planitis have worse vitritis, more severe macular edema, and a guarded prognosis compared to other patients with intermediate uveitis.
Infectious causes of intermediate uveitis include Epstein-Barr virus (EBV) infection, Lyme disease, human T-cell lymphotrophic virus type1 (HTLV-1) infection, cat scratch disease, and hepatitis C.
Differentiating Intermediate Uveitis from other Diseases
Associations of the disease with such entities as MS, sarcoidosis, or inflammatory bowel disease suggest an autoimmune component in at least a subset of patients. The clustering of familial cases has led to the investigation of human leukocyte antigen (HLA) associations. The inciting event appears to be peripheral retinal perivasculitis and vascular occlusion, leading to ocular inflammation, vitritis, and snowbank formation. The etiology of the antigenic stimulus is not clear and may be either vitreal or perivascular in nature. It is evident that genetics plays some role in the pathophysiology of intermediate uveitis, but the importance remains unclear.
Epidemiology and Demographics
In the United States the proportion of patients with intermediate uveitis is estimated to be 4-8% of uveitis cases in referral centers. The National Institutes of Health (NIH) reports a higher percentage (15%), which may indicate improved awareness or the nature of the uveitis referral clinic.
In the pediatric population, intermediate uveitis can account for up to 25% of uveitis cases.
Although intermediate uveitis can develop at any age, it primarily afflicts children and young adults. There is a bimodal distribution with one peak in the second decade and another peak in the third or fourth decade.
Natural History, Complications and Prognosis
Permanent loss of vision is most commonly seen in patients with chronic cystoid macular edema (CME). Every effort must be made to eradicate CME when present. Other less common causes of visual loss include rhegmatogenous retinal detachment, glaucoma, band keratopathy, cataracts, vitreous hemorrhage, epiretinal membrane, and choroidal neovascularization.