© Kirrawee Veterinary Hospital
CANINE DISEASES
Glaucoma
Glaucoma is an increase in the pressure within the eye. It mainly occurs in dogs but may also become apparent in cats.
The inside of the eye is mostly filled with a fluid (aqueous) which is being constantly produced within the eye in an area called the ciliary body. This fluid also flows out of the eye through small drainage holes to maintain the eye at a relatively constant intraocular (inside eye) pressure. Any imbalance through increased fluid production or reduced drainage can lead to glaucoma
Causes of glaucoma fall in to two broad categories:
- Primary Disease- glaucoma occurs without any disease being present in the eye and is due to an abnormal internal structure of the eye. This is similar to human glaucoma where the drainage reduces with time due to thickening of the surrounding tissues. It is called open angled glaucoma with goniodysgenesis. This is probably a condition that is present from birth but doesn't reach a critical stage until later in life. A number of breeds are more commonly effected including basset, Bouvier, cocker spaniel, elkhound, husky, dachshund, miniature poodles, chihuahua, and fox terrier breeds. This type of glaucoma is more receptive to medical treatment
- Secondary Disease- glaucoma occurs due to trauma or a disease within the eye that alters the internal structure.
Glaucoma is considered to be an emergency as vision may be lost within 24 to 72hrs. Typically the signs of glaucoma are a deep perilimbal hyperaemia (red eye), corneal edema (blue haze on the surface of the eye) and a semi-dilated pupil (central black area of the eye) that does not constrict in bright light. Signs of pain and general depression may develop.The pupil will become increasingly dilated and the eye may appear visibly enlarged.
Confirmation of glaucoma is obtained by tonometry (measuring the pressure within the eye) using specialised instruments which may require referral to specialist veterinary ophthalmologists. Pressures between 15-30mmHg are considered normal.
Treatment of glaucoma is initially medical to reduce the intraocular pressure and prevent permanent damage within the eye, however long term treatment generally requires corrective surgery.
Medical treatments include:
Intravenous Mannitol (1.5g/kg) or oral glycerin 2ml/kg which act as osmotic diuretics (drugs which drag fluid out of the body through the kidneys).
Drugs which reduce the production of aqueous including Dichlorphenamide, Ethoxzolamide and Acetazolamide (all oral carbonic anhydrase inhibitors),
1% epinephrine and 0.5% timolol maleate.
Drugs which increase drainage including 2% pilocarpine, echothiopate, and dimecarium bromide.
Surgical treatments may be used to open the drainage angle however long term control is usually achieved using cryosurgery (freezing) to destroy part of the ciliary body and reduce aqueous production permanently.
Not all eyes with glaucoma can be saved so surgical removal is not an uncommon outcome.
|