Noninfectious scleritis is an immune-mediated condition frequently involving the small blood vessels of the sclera. Pathophysiologic mechanisms vary according to the type of scleritis and underlying associated systemic disease. Onset is usually with infiltration of inflammatory cells in the sclera and episclera, mediated by proinflammatory cytokines and intercellular adhesion molecules.
The diffuse anterior subtype of scleritis is associated with a nongranulomatous response involving macrophages, lymphocytes, and plasma cells, which often assume a perivascular distribution.
In nodular scleritis, and particularly in necrotizing scleritis, the inflammatory response is more significant and specific, involving direct antibody-mediated damage (type II hypersensitivity), deposition of immune complexes triggering a type III hyper-sensitivity reaction, or a delayed (type IV) hypersensitivity response mainly characterized by granulomatous inflammation of the sclera. Inflammation may progress to an essentially vasculitic response, culminating in fibrinoid necrosis of the vessel wall and, eventually, necrosis of the sclera, episclera, conjunctiva, and cornea. Proinflammatory cytokines and activated metalloproteinases may play a role in local scleral and corneal damage.
Fong LP, Sainz de la Maza M, Rice BA, Kupferman AE, Foster CS. Immunopathology of scleritis. Ophthalmology. 1991;98(4):472–479.
Usui Y, Parikh J, Goto H, Rao NA. Immunopathology of necrotising scleritis. Br J Ophthalmol. 2008;92(3):417–419.
Excerpted from BCSC 2020-2021 series: Section 9 - Uveitis and Ocular Inflammation. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.