Chronic superficial keratitis
CSK is immune-mediated in nature, characterized by an infiltration of white blood cells into the superficial stroma of the cornea. These cells are predominately CD4-expressing T lymphocytes and to a lesser extent CD8-expressing T cells. The CD4-expressing T-cells secrete gamma interferon, which causes expression of the major histocompatibility complex class II molecules in the cells of the cornea. These class II molecules cause further inflammation by interacting with the T cells and triggering an immune response. Ultraviolet light is important in the genesis of the disease which is seen at higher prevalence at elevated altitude and has a seasonal variation with most cases occurring in the summer. There is likely also a genetic component to the cause of CSK due to its predominance in certain breeds.
Signs and symptoms
CSK is usually a bilateral progressive condition, however the lesions are not symmetrical nor are they painful. Signs include pigmentation and vascularization of the cornea (extension of blood vessels onto the cornea). It is usually first seen at the lateral (temporal) limbus (the junction between the cornea and sclera), although it eventually can extend from any part of the limbus to cover the entire cornea. Severe cases can cause blindness. Although CSK is usually identifiable by the appearance of the eye and the breed of the affected dog, cytology will reveal the presence of lymphocytes and plasma cells.
Treatment of CSK is usually with topical corticosteroids or topical cyclosporine, but any treatment only controls and reduces the inflammation rather than providing a cure. Other investigated treatments include pimecrolimus, a derivative of ascomycin that interferes with T cell activation and inhibits the production of inflammatory cytokines. Strontium-90 radiation therapy is also used to treat CSK. Canine sunglasses have also been used to help protect the eyes of dogs with CSK to prevent further damage from ultraviolet radiation.
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