Immune-mediated keratitis (IMMK) is a common non-infectious eye disease in horses. It is characterized by chronic corneal opacity in the absence of corneal ulceration or significant uveitis. There are four different levels of IMMK, based on the depth of the corneal lesion. These include epithelial, superficial stromal, midstromal, and endothelial. Superficial stromal keratitis is the most common type of IMMK.
IMMK usually occurs unilaterally, affecting just one eye. It is important to distinguish IMMK from other causes of keratitis, particularly infectious keratitis which can be of bacterial or fungal origin. IMMK generally affects only one eye, however it can affect both.