Juvenile idiopathic arthritis (JIA) is the most common childhood rheumatic disease and the most prevalent systemic disorder in children with uveitis [16, 17]. The common opinion is that JIA is a multifactorial autoimmune disorder, with a genetic predisposition that could be influenced by environmental factors and infections [18]. So far it is unknown which individual patient with JIA is at risk of developing uveitis except from antinuclear antibody (ANA) positivity and JIA subtype [19, 20]. JIAU is a serious visual-threatening disorder resulting in 15 % of blindness of affected eyes despite intensive treatment. It develops in approximately 20 % of all JIA subtypes, but in patients with oligoarthritis (less than 4 joints involved), the risk incidence increases to 41 % (Table 16.2) [21]. The peak incidence of JIAU is at the preschool age and girls are 3 times more often affected than boys [20]. It is characterized by a chronic anterior uveitis with insidious silent onset, and if the patients notice visual deterioration, there are already serious ocular complications. In the majority of the cases, uveitis is bilateral and the major site of inflammation is the anterior chamber, with or without keratic precipitates. Cells in the anterior chamber are a sign of active ocular inflammation, and in severe cases, anterior vitreous cells might be seen caused by spillover. Flare in the anterior chamber results from vascular leakage caused by damage to the blood aqueous barrier and ciliary body that can be measured with laser flare photometry [22]. Although clinically flare might persist, even in an inactive phase of uveitis, laser photometry flare reduces with aggressive treatment.

In most cases the uveitis is nongranulomatous but granulomatous characteristics have also been reported occasionally [23]. Severity of uveitis at presentation is by far and away the most important factor predicting a severe course and worse visual prognosis. In 1987 Wolf and later on Kanski identified that the eyes, which had posterior synechiae at presentation, had a worse visual outcome. Fifty-eight percent of these eyes had a final vision of 20/200 or worse compared with 3 % in the group with just flare and cells and keratic precipitates [24, 25]. Other clinical features, which define a severe course and a worse prognosis, are persistent inflammation despite intensive treatment, development of glaucoma, cataract requiring surgery, presence of cystoid macular edema, and recurrent episodes of ocular hypotony culminating eventually in blindness due to phthisis [26]. Hypotony is more common in JIAU than any other form of uveitis due to chronic inflammation and damage to the secretory ciliary epithelium [25].

Several baseline risk factors for a worse prognosis that have been identified for JIAU are male gender, young age at onset of disease, short interval between arthritis and uveitis, severity of uveitis at onset, and ANA positivity [22, 26–31]. In one study male gender was an independent risk factor for the development of blindness [29].

Sarcoidosis in children is a rare disease that clinically might be difficult to recognize and diagnose [45, 46]. In young children, sarcoidosis has mainly an extrapulmonary manifestation with a classic presentation of a triad with rash, arthritis, and uveitis, which might be indistinguishable from JIA [47–51]. Older children might have pulmonary and lymph node involvement comparable with the adult form. Renal involvement can occur at any age. Ocular inflammation might start as anterior uveitis, but during the course of the disease, posterior segment involvement might occur including multifocal choroiditis and choroidal granuloma, resulting in panuveitis [46]. The diagnosis of sarcoidosis can be confirmed by tissue biopsy of inflamed organs such as the skin or kidneys. Keratitis with multiple subepithelial corneal nebulae might occur in the early stage of sarcoidosis in preschool children [52]. In young children, granulomatous inflammation of several organs might be part of Blau syndrome which is characterized by familial granulomatous arthritis, uveitis, and skin granulomas. It is comprising an autosomal dominantly inherited syndrome that overlaps sarcoidosis. It is associated with mutations in the NOD2 (a.k.a. CARD15) gene on chromosome 16 [14].