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.
Three main points to remember
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?
Glaucoma can either be primary (breed related with a narrow drainage angle) or secondary (due to lens luxation, uveitis, neoplasia, pigment deposition, intraocular haemorrhage, after intraocular surgery).
What are the signs of glaucoma?
Glaucoma can affect either one or both eyes simultaneously. Depending on the inciting cause, if only one eye is affected, the other eye can be at risk in future of developing a similar problem.
Acute (fast onset) glaucoma can include:
- Pain, leading to shut eyes, tear streaming, head shyness, depression and anorexia
- Redness to the white of the eye (enlarged blood vessels)
- Vision loss in affected eye
- Cloudy appearance to the cornea (usually transparent surface of the eye)
- Dilated pupil in affected eye
- Chronic (ongoing) glaucoma can include these additional signs:
- Enlarged eyeball
- Lens luxation (lens falls forward in the eye, further reducing drainage)
- Retinal degeneration and detachment (seen on examination with an ophthalmoscope)
- Eventually the eye stops producing fluid, becoming non-functional and shrinks
How do we 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 kit 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 should be similar to each other in dogs.
How is glaucoma treated?
Since there are a wide variety of inciting causes of glaucoma, specific treatment options for each option are available, but all approaches share a common goal. The ability to preserve.
vision is achieved by bringing down the raised intraocular pressure as quickly as possible before more permanent damage is caused. Treated early, there is a possibility that the vision loss seen in acute glaucoma can be reversed, but unfortunately significant changes have often already occurred before presentation and many patients remain blinded in that eye.
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 is frequent application of topical prostaglandin analogues (e.g. Xalatan (R) or Travatan (R)), but these are contraindicated in cases where there is uveitis or lens luxation. In these cases, topical carbonic anhydrase inhibitors (Trusopt (R) or Azopt (R)) and application of topical steroids (Pred Forte(R)) can be of use.
Surgical management can also be considered, particularly in cases of lens luxation where the lens has fallen forward and is blocking the drainage angle. Intra-ocular surgery is a specialist procedure and if appropriate we can refer to a local centre for this in an emergency.
Unfortunately, in many cases medical and surgical management can be unrewarding and the pressure in the eye remains high and the eye remains non-functional and painful. If this is the case, then the best thing for the comfort of the patient is to remove the eye.
Even in cases where both eyes have been removed and the dog is completely blind, they can often cope remarkably well by relying on their other senses like smell, touch and hearing, which are far more acute than our own.
Are there any dog breeds which are predisposed to glaucoma?
Any breed of dog can have a secondary glaucoma, but a number of breeds are especially pre-disposed to primary (closed angle) glaucoma:
- Basset Hounds
- Cocker and Spinger Spaniels
- Great Dane
- Flat Coated Retrievers
What should I do if I suspect my dog has glaucoma?
If you are concerned that your dog 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.