Glaucoma is an eye disease which can affect both humans, dogs and many other mammals. It is characterised by optic nerve damage and loss of peripheral vision. In the vast majority of Glaucoma conditions the nerve damage is caused by rising pressure within the eye, so called intraocular pressure (IOP). The pressure within our eye is continually maintained through a balance of the amount of fluid being produced and the amount of fluid draining out of the eye. Providing these two elements balance each other out, then the intra ocular pressure remains stable. There are a number of different types of Glaucoma and these generally relate to how the pressure within the eye changes and the most common types are as follows:
Primary Open Angle Glaucoma:
This is by far the most common type of Glaucoma and is characterised by asymptomatic build-up of pressure within the eye. It is increasingly common as we get older and is generally caused by a reduced outflow of the fluid within our eyes. As I stated above, aqueous humour (eye fluid) is continually being produced and then drained from the eye. It is drained through a sieve like meshwork called the Trabecular meshwork. With age this structure can become thickened and small blockages can occur, meaning the fluid cannot drain away as well. As this progresses over time, the eye pressure slowly increases until it gets to the point where it starts damaging the optic nerve. Damage to the optic nerve leads to a slow loss of peripheral vision which again is generally not noticed until it gets quite extensive. The typical treatment for open angle Glaucoma is eye drops which are instilled daily and help keep the eye pressure at a normal level. In the rare cases that eye drops do not work, you will have to have to have either Glaucoma eye surgery or laser eye treatment.
Closed Angle Glaucoma:
This is a rare type of Glaucoma and is characterised by a rapid increase in eye pressure. Unlike open angle Glaucoma the symptoms of closed angle Glaucoma are extreme and you are likely to be in considerable pain, which comes on suddenly. Closed angle Glaucoma is not caused by a blockage in the trabecular meshwork as is in open angle Glaucoma. The blockage occurs between the iris and the cornea and is considered an ocular emergency as the pressure can rise to dangerous levels. If you suffer from this Glaucoma you will need to see an ophthalmologist as soon as possible, who will administer an injection in to your eye to rapidly reduce the pressure. Once the pressure has been reduced to a safe level your surgeon will have to perform laser treatment of your iris to prevent the blockage from occurring again.
Normal Tension Glaucoma:
This type of Glaucoma is the most difficult to detect as there is optic nerve damage in the absence of increased pressure. The exact causes are not known but it is thought that it is related to a decreased blood flow to the optic nerve. Treatment is more difficult with this type of glaucoma but it usually involves using similar eye drops that are used to treat open angle glaucoma.
Canine Glaucomas can often go unnoticed until they reach a severe state, this is due to a lack of clinical symptoms. This highlights the importance of regular eye examinations by qualified veterinarians. The only clinical symptoms of canine Glaucoma are that the dog may rub the eye if it is painful. An affected eye may also be red, swollen, sore, or become clouded in appearance.
Predisposed breeds include:
- Cocker Spaniels
- Jack Russell Terriers
- Bassett Hounds
This is not to say that primary Glaucomas have not been observed in other breeds, nor is it to say that the above breeds will definitely develop a Glaucoma – just that their genetics make them more likely to develop.
Diagnosis & Treatment
There are three primary methods used by veterinarians of diagnosing Glaucomas; tonometry (measurement of IOP), gonioscopy (Examination of the angle in the anterior chamber) and ophthalmoscopy (evaluation of the retina and optic nerve).
Treatment is similar to that given to humans; laser surgery (to selectively destroy tissue), enucleation (removal of the eye), intra-ocular evisceration & implantation (removal of the inner contents of the eye – the outer portion remains) and shunts (a method to remove pressure from the eye).
Glaucoma is generally considered the silent disease (excluding closed angle glaucoma) as most people who have the condition are completely unaware. Having regular eye tests is the only real way of detecting the condition and providing it is picked up early enough it can generally be treated or controlled to the point that it will never affect your vision. During an eye test your optometrist will assess the health of your optic nerves, measure your intraocular pressure and check your peripheral vision. If any of these are found to be suspicious you will be referred to a glaucoma specialist.
This article was written by an Optometrist, Tim Harwood who has over 10 years’ experience of screening people for Glaucoma. He also writes the content for his own website Treatment Saver which helps people make the right decision about their health which includes a Question and Answer feature and many well written guides. As an optometrist, Tim is a passionate about encouraging people to get their eyes tested regularly, regardless of whether they think they having any problems or not. Glaucoma is after all the silent disease!