Paul Adams has a long-standing interest in ophthalmology, gaining his post-graduate certificate in 2011. Over the next few months he will be discussing a range of eye conditions that are commonly seen in general practice with the intention of trying to demystify the eye.
Glaucoma is a condition of the eye that can occur in both dogs and cats, although the latter are far less commonly affected.
It can happen quite suddenly (acute) although many of these cases are thought to occur in an eye which has chronic glaucoma that has simply not been detected. There are several breeds predisposed to the condition including Cocker Spaniels, Jack Russell Terriers, Bassett Hounds, Beagles, Samoyeds and the Chow Chow.
The disease may be described as primary when there is a genetic abnormality in the drainage apparatus of the eye. This prevents fluid draining as it should and so, with normal volumes of intra-ocular fluid still being produced, there is an overall increase in the pressure within the eye.
Secondary glaucoma can occur following lens luxation (the dislocation of the lens from the normal position in the eye), inflammation of the tissues within the eye (for example in infection), tumours or if blood collects in the front of the eye following a trauma.
Clinical signs of glaucoma are often very subtle initially and can be easily missed but may include redness or engorgement of the vessels in the whites of the eyes and a cloudy appearance of the eye. The pupil is often fixed and unresponsive to light.
Glaucoma is a very painful condition because of the high intra-ocular pressure but if left untreated, this pressure also results in damage to the optic nerve and retina, leading to blindness.
A diagnosis is made simply and non-invasively using a tonopen to measure the intra-ocular pressure. Gonioscopy can also be performed and uses a special lens to allow direct visualisation of the drainage angle.
This enables the glaucoma to be classified (open, narrow or closed angle) and help determine if medical or surgical management is appropriate.
Medical management includes drugs to reduce the pupil size and open up the drainage angle, the administration of special intra-venous fluids and topical eye drops to reduce fluid production; if the overall volume of fluid in the eye can be reduced, this will lower the intra-ocular pressure.
Long term management of narrow or closed angle glaucoma often requires surgery to divert fluid or help open the drainage angle. Close monitoring of intraocular pressures should follow.
Often both eyes are affected but not always. Taking steps to protect the other eye is advised as around 40% of dogs will become blind within a year, despite medical and/or surgical intervention.
Where this happens and the pressures cannot be controlled, enucleation (removal of the eye) is advised.
Prevention is better than cure and as part of our annual pet MOT, Knutsford Veterinary Surgery routinely monitor the intraocular pressures of at risk breeds.
If this article has raised and questions or concerns, then please do not hesitate to contact Paul and his team on 01565 337999, via email on Paul@knutsford.vet or in person in his surgery.