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 most common type is simple episcleritis, in which there are intermittent bouts of moderate to severe inflammation that often recur at 1-3 month intervals. Prolonged episodes may be more common in patients with associated systemic conditions.
Some patients note episodes are more common in the spring or fall.
The precipitating factor is rarely found, but attacks have been associated with stress and hormonal changes. Patients with nodular episcleritis have prolonged attacks of inflammation that are typically more painful than simple episcleritis. Many patients with nodular episcleritis have an associated systemic disease. Most common in the fourth to fifth decades. Many patients complain of acute onset of mild to moderate discomfort although some may notice an area of painless injection.