Episcleritis is an inflammatory condition affecting the episcleral tissue that lies between the conjunctiva and the sclera. [1, 2] It is usually a mild and self-limiting but recurrent disease. Most cases are idiopathic, although up to one third may have an underlying systemic condition. Some cases may be caused by exogenous inflammatory stimuli. [3, 4, 5]
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 of episcleritis are diffuse and nodular/focal.
The most common type is diffuse episcleritis, in which there are intermittent bouts of moderate-to-severe inflammation that often recur at 1- to 3-month intervals. The episodes usually last 7-10 days, and most resolve after 2-3 weeks. Prolonged episodes may be more common in patients with associated systemic conditions. Some patients note that episodes are more common in the spring or fall. The precipitating factor is rarely found, but attacks have been associated with stress, allergy, trauma, and hormonal changes.
Patients with nodular/focal episcleritis have prolonged attacks of inflammation that are typically more painful than diffuse episcleritis. Many patients with nodular episcleritis have an associated systemic disease. 
Diffuse episcleritis (70% of cases) is more common than nodular scleritis (30% of cases), and the mean age of patients is 47.4 years.  Unilateral inflammation is seen in two thirds of patients with episcleritis. Episcleritis is more common in females than in males, although the difference is not statistically significant. [7, 8]
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