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Nonulcerative Keratitis in Cats

Keratitis is the medical term given to inflammation of the cornea -- the clear outer layer of the front of the eye. Nonulcerative keratitis is any inflammation of the cornea that does not retain fluorescein stain, a dye that is used to identify ulcers of the cornea. If the very top layer of the cornea has been disrupted (as with an ulcer), the dye will enter the lower layers of the cornea and will cause a temporary stain that glows under an ultraviolet light; in nonulcerative keratitis, the top layer of the cornea is not disrupted, so no dye enters the lower layers of the cornea.

Long-term superficial inflammation of the cornea may occur at any age, but the risk is higher between the ages of four to seven years. There are different forms that nonulcerative keratitis can take. Inflammation involving the area where the cornea (clear part of the eye) and the sclera (white part of the eye) come together, and characterized by the presence of nodules, may occur. Another is a condition in which part of the corneal tissue dies, leaving a pigmented lesion and fluid build-up. These forms can occur at any age, but the latter form is most prevalent in Persian, Siamese, Burmese, and Himalayan breeds. There is no proven genetic basis in cats that has been found so far. However, geographical location has been found to play some role, as animals living at higher altitudes appear to be at increased risk.

Herpesvirus in cats can affect cats of all ages and can lead to inflammation of the cornea. This form is characterized by the presence of a type of white-blood cell called an eosinophil (condition known as eosinophilic keratitis) and results in a condition in which part of the corneal tissue dies, leaving a pigmented lesion and fluid build-up in the eye. This can occur at all ages except in newborns.

Symptoms and Types

• Herpesvirus (nonulcerative; involves the thick, clear middle layer of the cornea)
  • May involve one or both eyes
  • Often occurs with ulceration
  • Fluid build-up in the cornea
  • Infiltrates and encroachment of blood vessels into corneal tissue
  • Scarring - may threaten vision, if scarring is severe
• Inflammation of the cornea, characterized by the presence of a type of white-blood cell called an eosinophil
  • Usually involves only one eye
  • Appears as raised white, pink, or gray corneal plaque with roughened surface
  • May retain fluorescein stain at the edge of the lesion
• Condition in which part of the cornea tissue dies, leaving a pigmented lesion and fluid build-up
  • Usually involves only one eye but can involve both eyes
  • Appears as amber, brown, or black oval to circular plaques near the center of the cornea
  • Can vary in size and corneal depth
  • Edges may appear raised because of fluid build-up in the cornea
  • Thickened tissue
  • Encroachment of blood vessels into corneal tissue is variable
  • May retain fluorescein at edge of lesion
• Variable discoloration of the cornea
• Variable eye discomfort

Causes

• Herpesvirus – the nonulcerative keratitis is believed to be an immune-mediated reaction to the herpesvirus antigen rather than an actual effect of the viral infection
• Inflammation of the cornea, characterized by the presence of a type of white-blood cell, called an eosinophil – cause is unknow but may be secondary to herpesvirus infection
• A condition in which part of the cornea tissue dies, leaving a pigmented lesion and fluid build-up – cause is unknown, but is likely due to long-term corneal irritation or previous trauma