Around 50% of cases of uveitis are classified as idiopathic, while many of the others are associated with or form part of other disease entities.12 Idiopathic uveitis comprises a spectrum of CD4⁺ T cell mediated MHC class II restricted, chronic autoimmune intraocular inflammatory conditions,3the underlying immunological effector mechanisms of which have many features in common with systemic conditions associated with intraocular inflammation—for example, sarcoidosis, Behçet’s disease, seronegative spondyloarthropathies, and multiple sclerosis.4 Therapy for these conditions must be tailored to treat both ocular and systemic disease, although successful immunosuppression for the ocular inflammatory component can be achieved using the same approach as for idiopathic chronic intraocular inflammation, especially if the systemic component is inactive.5 Recognising whether intraocular inflammation is idiopathic or associated with systemic disease either at the time of presentation or in the future is difficult. For example, the term “intermediate uveitis”, which includes pars planitis, not only embraces an undetermined number of disease entities, but is frequently associated with underlying systemic diseases such as sarcoidosis and multiple sclerosis. Thus a major management problem which commonly arises is because the presently available clinical tests cannot predict whether patients with intermediate uveitis have or will develop an associated systemic disease. It is well recognised that in sarcoidosis up to 30% of cases present with uveitis, sometimes years before the onset of clinical signs of the …