Corneal Inflammation (Nonulcerative Keratitis) in Dogs

Nonulcerative Keratitis in Dogs

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. Keratitis is the medical term given to inflammation of the cornea — the clear outer layer of the front of the eye. 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.

In long-term superficial inflammation of the cornea (keratitis), also known as pannus, there may be an inherited susceptibility in the German shepherd and the Belgian Tervuren. 

Long-term superficial inflammation of the cornea may occur at any age, but risk is higher between the ages of four to seven years. There are different forms that nonulcerative keratitis can take. Inflammation characterized by the presence of pigment that is deposited in the cornea is sometimes seen in short-nosed, flat-faced (brachycephalic) breeds of dogs, and can occur at any age. In these cases, inflammation of the cornea may be due to exposure to airborne irritants, from a condition in which the eyelids do not close completely, and where there are tear-film deficiencies. Other possible causes include prominent folds of skin around the nose, or abnormal eyelashes that turn inward against the cornea (entropion), which has been notably identified in pugs, Lhasa apsos, shih tzus, and Pekingese.

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 in any breed, but is more likely to affect cocker spaniels, greyhounds, collies and Shetland sheepdogs. This form can occur at any age, but varies sometimes by breed. In collies, the average age of occurrence is between three and four years.

Dry eye is often seen in short-nosed, flat-faced (brachycephalic) breeds, notably cocker spaniels, English bulldogs, Lhasa apsos, shih tzus, pugs, West Highland white terriers, Pekingese, and Cavalier King Charles spaniels. This condition is generally diagnosed in middle to older aged dogs. 

Although breed predilection appears to play a role, there is no proven genetic basis in dogs 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.

Symptoms and Types

• Long-term (chronic) superficial inflammation of the cornea
  • Usually involves both eyes Symmetrical pinkish white lesions with variable pigmentation
  • Usually seen on the outer and/or lower part of the cornea
  • Third eyelids may be affected and appear thickened or depigmented
  • White lipid (a group of compounds that contain fats or oils) deposits may be present at adjacent corneal edge
  • May lead to blindness in advanced disease
• Inflammation characterized by the presence of pigment that is deposited in the cornea Appears as diffuse brown to black discoloration of the cornea
  • Often associated with encroachment of blood vessels into corneal tissue or scarring
• Inflammation usually involving the area where the cornea (clear part of the eye) and the sclera (white part of the eye) come together
  • Characterized by the presence of nodules
  • Usually involves both eyes; raised pink to tan lesions of the outer part of the cornea
  • May be slowly to rapidly progressive
  • White deposits and encroachment of blood vessels into corneal tissue may occur in adjacent corneal tissue
  • Third eyelids may appear thickened
• Dry eye
  • Variable findings
  • May involve one or both eyes
  • Discharge from the eye(s) may contain mucus and/or pus
  • Redness of the moist tissues of the eye
  • Encroachment of blood vessels into corneal tissue
  • Pigmentation
  • Variable scarring
• Variable discoloration of the cornea
• Variable eye discomfort

Causes

• Long-term superficial inflammation of the cornea is presumed to be immune-mediated Higher altitudes and solar radiation increase the likelihood and severity of the disease
• Inflammation characterized by the presence of pigment that is deposited in the cornea secondary to any long-term corneal irritation
• Possible primary underlying eye conditions
• More frequently associated with exposure to corneal disease and dry eye
• Inflammation usually 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 is presumed to be immune-mediated/
• Dry eye is usually caused by immune-mediated inflammation of the gland that produces tears

Diagnosis

Your veterinarian will perform a thorough physical and ophthalmological exam on your cat, taking into account the background history of symptoms and possible incidents that might have led to this condition. A culture of the fluid in the eye will need to be done. Infectious keratitis is generally easy to diagnose because it is typically ulcerative and painful, distinguishing it from nonulcerative keratitis. If the problem is a tumor, the cornea and sclera are rarely involved. Usually, symptoms will only be on one side. The culture of the cells in the fluid will confirm the diagnosis, and will require a further analysis of the affected eye tissue. A biopsy of the cornea will be done if there are nodules, or if cancer is suspected.