Diseases of the canine Sclera and Episclera

Episcleritis

In dogs diffuse episcleritis is seen infrequently and has not been associated with systemic disease (Fisher 1983). Some animals have a dramatic influx of lipid into the cornea (Crispin 1991). Nodular granulomatous episclerokeratitis (NGE) is seen as 1) a distinct raised red gray mass at the corneoscleral junction and infiltrating adjacent corneal stroma, 2) focal areas of corneal stromal degeneration and 3) involvement of the nictitating membrane (Fisher 1983). NGE is responsive to surgical excision and intra-lesional injection of corticosteroids (Fisher 1983). NGE has a good response to oral azathioprine (Imuran®, Wellcome) in conjunction with topical corticosteroids (Whitley and Gilger 1999). Secondary epicleritis may result from panophthalmitis, chronic glaucoma or ocular trauma (Fisher 1983).

Scleritis

Dogs with scleritis usually have brawny tan-colored sector lesions arising near but posterior to the limbus and there may be edema of the adjacent cornea (Fisher 1983). If uveitis is present it is non-granulomatous (Fisher 1983).There may be involvement of the posterior sclera and uvea resulting in fundus lesions (Fisher 1983). A recent histopathological study found that extension of scleritis to involve the uvea was common (Deykin et al 1997). Typical canine scleritis consists of granulomatous inflammation with infiltration of lymphocytes, plasma cells and epitheloid cells (Fisher 1983). Necrosis of the scleral collagen is not characteristic (Fisher 1983). After a number of episodes of sleritis in one dog scleral thinning developed (Fisher 1983). Phenylephrine 10% instilled into the conjunctival sac constricts superficial conjuctival and episcleral vessels, enabling examination of the sclera (Crispin 1991). Crispin (1991) has proposed a differentiation of scleritis into diffuse vs nodular. Diffuse scleritis is rare and patients may have present a degree of proptosis because of thickening of the sclera; the inflamed tissue has a bluish red hue (Crispin 1991). Both nodular episcleritis (NGE) and diffuse scleritis are characterised by a granulomatous response that is characterized by collagen degeneration (Deykin et al 1997).

This page was authored by T. F. Evans October 2000.