Primary inflammatory conditions of the sclera and episclera are immune-mediated disorders characterized by hyperemia and thickening of the fibrous outer tunic of the globe. These conditions may be difficult to distinguish clinically from conjunctivitis or glaucoma. The diffuse form of scleritis is seen most commonly in the Cocker Spaniel and may extend posteriorly with choroidal involvement and (rare) secondary retinal degeneration. The distinction between conjunctival and scleral vascular engorgement can be made by gently moving the conjunctiva with a cotton-tipped swab after application of topical anesthesia.
Scleritis and episcleritis may be difficult to distinguish clinically from conjunctivitis or glaucoma. Keys to differentiating this from glaucoma are the absence of corneal edema and normal pupillary light response. As glaucoma is both more common and more devastating to vision, if in doubt about the diagnosis, confirmation by accurate measurement of intraocular pressure should be obtained.
More commonly, scleritis occurs regionally with a proliferative response of inflammatory cells and granulation tissue which may extent into the cornea. A biopsy is diagnostic with dense accumulation of plasma cells and lymphocytes.
A more localized form of this condition occurs most commonly in the Collie breeds and presents as a markedly raised, nodular lesion at the limbus (usually temporally). These masses rapidly enlarge leading to concern about a neo-plastic process. Partial excision may be performed with histopathologic confirmation of the diagnosis.
Severe forms of scleritis may progress with posterior segment involvement (secondary chorioretinal degeneration), scleral thinning, ulcerative keratitis and corneal dystrophy.
Treatment involves anti-inflammatory medications (corticosteroids, cyclosporine, azathioprine) given topically, subconjunctivally and occasionally systemically. Most cases respond well to a single subconjunctival injection of 4-8 mg triamcinolone with continued topical 1% prednisolone suspension once or twice daily. The topical medication is reduced in frequency slowly over 2-3 months although many cases require life-time (once daily to every other day) therapy.