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.
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 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. Photophobia and watery discharge may be noted. A diffuse or localized injection of the bulbar conjunctiva is often present.