What The Cornea Does
The smooth, transparent cornea allows light to penetrate and reach the retina and acts as a barrier protecting the delicate internal eye structures. Any change to the surface of the cornea diminishes eyesight. Some corneal problems, for example the development of dark, light-occluding pigmentation, are insidious. They cause no pain and a dog does not complain. Other conditions do cause pain and are diagnosed earlier.
Corneal Damage - Abrasions And Ulcers - Ulcerative Keratitis
Because of the nature of our pets, the corneas are prone to damage. When the surface is scratched local swelling occurs causing a cloudy or hazy, opaque appearance. Abrasions often develop into ulcers. Physical injury causes abrasions. Ulcers may be caused by physical injury but are also associated with:
- Dry eye in dogs (keratoconjunctivitis sicca)
- Viral infections in cats
- Sugar diabetes (diabetes mellitus)
- Underactive adrenal gland (hypoadrenocorticism)
- Underactive thyroid gland in dogs (hypothyroidism)
- Breed predisposition in dogs
- Corneal damage is usually painful. A pet squints or keeps the affected eye slightly closed. It becomes inflamed and initially tears in excess. Secondary infection is common and produces a purulent discharge.
Diagnosis and treatment
The full extent of corneal injury is visible when fluorescent dye is applied to the cornea. All damaged areas take up the dye. Even the slightest abrasion requires our immediate attention. Treatment may simply be prophylactic topical antibiotic. In other instances topical atropine is used, to dilate the pupil and relieve pain. Surgery is often necessary for ulcers. Either the third eyelid or a flap of conjunctiva is protectively sutured over the ulcerated region. Soft contact lenses, specially designed for a pet's eyes, may also be used as protection. A bubble-like bulge in an ulcer means the ulcer is about to burst and the liquid content of the anterior chamber discharge. Urgent surgery is needed to save the eye.
Pigmented Keratitis In Pekes And Pugs
These breeds often develop a generalised form of pigmented keratitis, beginning at the nose side of the eyeball (medial canthus) and spreading laterally. This is caused by chronic irritation from the nasal fold. Trimming the hair on the nasal fold reduces corneal irritation. The best way to treat this condition is to surgically remove the fold of nasal skin.