When the pressure is on!
Veterinary Tonometry - Written by Veterinarian Elaine McIlhinney
We have recently invested in a handheld veterinary tonometer at the practise. This vital piece of equipment has now become an integral part of our routine eye exams here at Mill Road and it only takes a minute or two to do! It is vital in the diagnosis, prevention and management of glaucoma. It also allows us to communicate and follow up more effectively with our veterinary eye specialist, Peter Collinson, who is based in Auckland; Peter has been a wonderful support to the vets at Mill Road and has seen many of our patients who have required his expertise.
Glaucoma occurs when there is an increased intraocular pressure (IOP). This can be a primary condition in some breeds such as poodles and beagles or more commonly, occurs secondary to other disease processes. It is also useful to diagnose uveitis which is another potentially blinding eye condition secondary to an array of underlying causes.
Fluid (aqueous humour) is continually produced by the ciliary body in the iris. It fills the anterior and posterior chamber of the eye and in normal circumstances drains away through the drainage angles at the same rate it is produced. When this fluid does not drain due to blockage of the drainage angles, pressure rapidly builds up. This can quickly result in blindness due to pressure on the optic nerve at the back of the eye.
Most eye problems manifest themselves in the same way – a red eye. The pressure should always be measured in these red eyes, unless there is an obvious reason for the pain such as a scratch to the cornea. Dogs with glaucoma developing is often lethargic or quiet due to a ‘headache’ sensation. They may or may not be off food. This can be more difficult to tell with cats.
Animal eye pressure measuring is quick and easy with the handheld, small TONOVET tonometer. Painless measurement is barely noticed by the animal and does not require application of anaesthetic eye drops. There is no unpleasant feeling of air whooshing on to the eye. Most animals are held loosely by their owners while we check these. In fact, if animals need to be heavily restrained, there IOP will temporarily go up. So the best way is to have a super relaxed animal minimally restrained which is actually the norm for this test.
Here at Mill Road we have measured IOP in dogs, cats and rabbits. Normal ranges sit between 10-20mmHg and there is usually a similar reading for both eyes.
Eye pressure should be considered in:
-Young patients to establish baseline readings
-Patients older than 6-7 years
-Patients predisposed to glaucoma (42 canine breeds)
-Ocular examination patients
-Head or eye trauma patients
If you have any concerns about your pets’ eyes you can mention this at their annual health check or when you next visit the clinic and we can advise you if this test is required.