What is Glaucoma?
Glaucoma is a disease in both animals and humans which often causes blindness and is due to an increase in pressure in the eye. The pressure in the eye, intraocular pressure (IOP), can be measured and is normally between 15-25 mm of mercury. In glaucoma, the pressure increases because of a failure of drainage of the fluid which is continuously produced inside the eye. The increased IOP can rapidly (within 24 hours) cause blindness, and also pain. Vision loss occurs because of pressure damage to the optic nerve.
What causes Glaucoma?
Pressure within the eye is influenced by all contents of the eye. However, the generation of the fluid within the front of the eye (the “aqueous humour”) is most relevant for glaucoma. The aqueous humour is produced constantly. Glaucoma is invariably due to the lack of drainage from the eye.
Glaucoma can be either primary or secondary. Primary glaucoma occurs in certain breeds with anatomically faulty drainage facilities within the eye, and is often inherited. Breeds such as Basset Hounds, Cocker Spaniels, Australian Cattle Dogs, Fox Terriers, Poodles and Burmese cats are breeds which may develop primary glaucoma. Secondary glaucoma is caused by some other problem, such as inflammation (uveitis), lens luxation, trauma, or cancer inside the eye. In these cases treatment of the underlying problem may help treat the glaucoma.
What are the clinical signs of Glaucoma?
The usual presentation is a dog with a blind, painful, red eye with a blue or cloudy cornea. Unfortunately glaucoma can look like a simple “conjunctivitis”, so if your pet has any of these signs please call your veterinarian or eye specialist. Early detection of glaucoma may be difficult. In humans, in the early stages, there are often subtle vision problems. In animals these subtle vision problems are very hard to detect. Unfortunately many of the cases of glaucoma we see are well advanced by the time of the first visit.
What treatments are available for Glaucoma?
Medical treatment with eye drops and oral drugs may successfully control the problem in the short term, or when the pressure increase is minimal. However long lasting control or a permanent solution usually requires surgery. The type of surgery varies from case to case. As a general rule of thumb, if the eye still has potential for vision, then surgery to decrease the IOP is used. If the eye is irreversibly blind, we may recommend either a prosthesis in the eyeball itself, or eye removal. The reason for this is that chronic glaucoma is painful, and in an eye that is non-visual this is the kindest option available to your pet. The surgical options to reduce pressure in the eye are many and varied. In a visual eye, the ideal treatment is an endocyclophotocoagulation where we can use a microsurgical camera to insert in to the eye, and view the portion of the eye that is responsible for producing aqueous humour. We can then use a surgical laser to selectively destroy this portion of the eye, so the ability to generate aqueous humour is stunted. This procedure is very technically demanding and instrument-intensive, but gives our best chances of vision retention long-term. An alternative procedure involves using a laser to apply to the external surface of the eye (trans-scleral cyclophotocoagulation), also to destroy the same region, but this method is less accurate and so does not have results as promising as the internal laser method. However, this method is less technically challenging and less instrument intensive.
Humans say that suffering from glaucoma is like having a migraine. Dogs and cats are often quite good at hiding their discomfort. It is often only when a glaucomatous blind eye is removed or has a prosthesis that the owners realise how painful it must have been, as the animal is rejuvenated, more active and alert. If detected early, we can minimise the effects of glaucoma, and prolong vision as long as possible, or even prophylactically prolong the onset of glaucoma in some animals.
Can we prevent Glaucoma?
In many cases of glaucoma in one eye, there is a reasonable chance that the normal eye may also be affected later on. Therefore we recommend regular rechecks (every 3-4 months) to monitor the IOP in the normal eye as well as monitoring the affected eye. We may even recommend that the normal eye is kept on lifelong prophylactic medications.