Contributor: Gordon K. Klintworth
Scleritis is uncommon may occur in the absence of an underlying ocular disease [scleritis - primary] or it may complicate an ocular disorder [scleritis - secondary]. Primary scleritis tends to present clinically in the anterior [scleritis - primary anterior] or posterior [scleritis - primary posterior] part of the sclera, but the lesion may begin more diffusely and spread from one part of the sclera to another. The tissue reaction may involve not only the scleral collagen, but also the blood vessels and nerves that traverse the sclera.
For clinical reasons several types of scleritis are recognized (episcleritis, anterior scleritis [scleritis - anterior] nodular scleritis [scleritis - nodular], diffuse scleritis [scleritis - diffuse] and necrotizing scleritis [scleritis - necrotizing]). One form of scleritis may progress to another. |
Scleritis is often a manifestation of a systemic disease and in most instances (~87% of cases) it is an autoimmune disease in a genetically predisposed host (rheumatoid arthritis, Wegener granulomatosis, relapsing polychondritis, polyarteritis nodosa, systemic lupus erythematosus, inflammatory bowel disease, Churg-Strauss syndrome, Behçet disease, cranial arteritis, Cogan syndrome, ankylosing spondylitis, Reiter syndrome) . Rheumatoid arthritis is the most frequent associated disorder (10-33% of cases). An autoimmune vasculitis [vasculitis - autoimmune] appears to have an important pathogenetic role in the scleritis that occurs in these conditions and it is noteworthy that the first areas affected clinically tend to be where the anterior and posterior blood vessels pass through the sclera. Studies on biopsied conjunctival and scleral tissue in patients with a necrotizing scleritis or recurrent non-necrotitizing scleritis have disclosed an obliterative immune complex vasculitis. The vasculitis is characterized by fibrinoid necrosis and the invasion of the vascular walls with neutrophils. 
Aside from the autoimmune diseases scleritis may be associated with other conditions (tuberculosis, syphilis, gout, ochronosis). A rare cause of scleritis is sarcoidosis. Life expectancy after the onset of scleritis may be <10 years because of the associated systemic disease.
Frequently scleritis is secondary to an inflammatory reaction that originates in the conjunctiva [conjunctivitis], the uvea [uveitis], orbit, or other contiguous structures.
Scleritis is more severe than episcleritis and more often leads to a loss of vision from associated complications (keratitis, uveitis, cataract, glaucoma, retinal detachment). When do to a pathogenic organism the infection can spread extraocularly via intrascleral perforating blood vessels and nerves. After healing the focally or diffusely affected sclera may become thin and lead to the formation of a staphyloma. Its severest form is scleromalacia perforans. Often such a perforation is a late manifestation of the scleritis and occurs after the inflammatory reaction has subsided. Chronic, recurrent anterior scleritis may extend posteriorly to involve the pre-equatorial and equatorial sclera and the thickened scleral mass in the region of the pars plana of the ciliary body and of the anterior choroid may resemble a scleral buckle or a uveal melanoma [melanoma - uvea] or other intraocular neoplasm.