The eyes of our domestic pets have a structure and function very similar to our own eyes.
This means they can have the same eye problems that humans can develop including cataracts, glaucoma and corneal ulceration.
The eye is a complex organ that constantly adjusts to provide a clear image to the brain. If any part of the eye is not functioning well it can affect sight.
Glaucoma is a condition that can be acute (sudden onset) and quickly cause blindness and if left untreated causes ongoing pain and distress.
Please read through our frequently asked questions and be aware of the three main points to remember:
- Know the signs of glaucoma
- Speed of diagnosis is crucial to success, so if in doubt come see us!
- Glaucoma is a serious and potentially blinding condition and intensive treatment (and possibly referral to a specialist ophthalmologist) may be necessary
What is Glaucoma?
Glaucoma is defined as a raised pressure inside the eye.
In a healthy eye the intraocular pressure is maintained by a constant cycle of production and drainage of the fluid in the front (anterior) chamber of the eye.
In dogs and cats an increase in intraocular pressure is caused by failure of the drainage system of the eye.
What are the common causes of glaucoma?
Primary glaucoma (breed related with a narrow drainage angle) is very rare in cats.
Secondary glaucoma in cats is most commonly due to uveitis (intraocular inflammation) or intraocular neoplasia (tumours such as lymphoma or melanoma).
What are the signs of glaucoma?
Glaucoma can affect either one or both eyes simultaneously. Depending on the inciting cause, even if only one eye is currently affected, the other eye can be at risk in future of developing a similar problem.
Cats tend to present with the following signs:
- Enlarged eyeball
- Dilated pupil
- Uveitis (inflammation of the front portion of the eye)
Despite being a painful condition, cats tend to be very adept at hiding this fact. Subtle signs of hiding away, becoming less affectionate than normal and reduced grooming can be seen.
How do you diagnose glaucoma?
We can perform a full clinical examination including an ocular examination to evaluate the disease. If we are suspicious of glaucoma, we can measure the pressure inside the eye by using a special piece of equipment called a Tonopen.
This is a very delicate piece of equipment that (having applied a local anaesthetic drop to the eye) is gently tapped directly on the surface of the cornea. The tip of the machine reads the amount of pressure taken to flatten the corneal surface and thus the intraocular pressure.
The normal pressure inside the eye of our domestic pets is between 10-25 millimetres of mercury (mmHg); the pressure of each eye can differ from each other by up to 10mmHg in cats.
How is glaucoma treated?
Cats tend to try to hide signs of pain and for this reason glaucoma is often not picked up until the disease has progressed, making medical treatment more challenging and in many cases patients will remain blind.
Medical treatment needs to be intensive and instigated quickly to stand a chance of working well. This is often best done in hospital but can sometimes be performed at home, especially if irreversible changes have already occurred. In most cases application of drops to the surface of the eye can help to quickly reduce the pressure inside the eye.
The most effective medical therapy in cats is frequent application of topical carbonic anhydrase inhibitors (Trusopt (R)) but even this is often ineffective. Other options such as topical beta blockers and prostaglandin analogues that can be useful in other species have been shown to have little effect in cats.
The damage to the structures of the eye suffered by the increased pressure can in some cats induce a tumour called “post-traumatic sarcoma” to form.
To prevent this problem, enucleation (removal of the eye) is often indicated, particularly where the eye is painful due to ongoing increased intraocular pressure. Cats can cope surprisingly well with one eye as they can rely on their other senses including hearing, touch and smell, which are far more acute than our own.
Are any breeds of cat predisposed to glaucoma?
Primary glaucoma (as seen in dogs) is very rare.
Any breed of cat can have a secondary glaucoma but breeds including Siamese, Burmese and Persian are particularly susceptible.
What should I do if I suspect my cat is suffering from glaucoma?
If you are concerned that your cat is showing any of the signs of glaucoma, then call us immediately to ask for advice. You may need to be seen straight away, as treatment is best started as soon as possible to preserve eye function.