Episcleritis is an inflammatory condition affecting the episcleral tissue that lies between the conjunctiva and the sclera. It is usually a mild, self-limiting, recurrent disease.
Most cases are idiopathic, although up to one-third have an underlying systemic condition.
Some cases may be caused by exogenous inflammatory stimuli. The pathophysiology is poorly understood. The inflammatory response is localized to the superficial episcleral vascular network, and histopathology shows nongranulomatous inflammation with vascular dilatation and perivascular infiltration. The 2 clinical types are simple and nodular. Prolonged episodes may be more common in patients with associated systemic conditions.