What is Glaucoma?
Glaucoma is the increase of pressure inside the eye. The eye is a fluid filled structure where the fluid is used to maintain eye shape and provide nourishment to the tissues in the eye. Glaucoma happens due to decreased drainage of fluid from the eye and to a smaller porition, increased production of fluid. Intraocular pressure (IOP) is the measurement of pressure inside the eye and the normal range for dogs and cats are 10-20mmHg. Rabbits and Guinea Pigs are 15-23mmHg.
What Causes Glaucoma?
Glaucoma can be categorised according to their causes.
Primary glaucoma is an increased internal eye pressure in a healthy and normal eye. This means to say that this condition is due to genetics that causes anomalies in the internal structure of the eye. Breeds that are more commonly affected are Beagles, Cocker Spaniels, Shih Tzus, Jack Russell Terriers and several others. This form of glaucoma is rare in cats.
Secondary glaucoma is when the pressure in the eye is increased due to an injury or disease. Common causes are inflammation in the eye (uveitis), cataracts, trauma to the eye such as cat scratches or external injuries, tumors/growths in or behind the eye, lens displacements and diseases such as Feline Infectious Peritonitis in cats or Tick Fever in dogs.
What are the Symptoms?
- Painful eye – squinting or frequent rubbing of the eye can signify pain. Your pet may also try to avoid letting you near the affected eye. As pressures in dogs and cats can go up to 30-50mmHg, it can be very painful.
- Red eye – look for any redness on the whites of the eye
- Bulging of the eye – it is most obvious if one is bigger than the other or looks to be bulging out of the head. However this can be difficult to differentiate.
- Cloudy cornea – surface of the eye looks whitish or bluish in colour
- Sudden blindness – knocking into household items or seems apprehensive to go out for walks. Sometimes if the pet is only blind in one eye, owners may not notice as they are able to compensate well with their other eye. Blindness occurs due to pressure damage on the optic nerve.
- Inappetence – this can occur if your pet is unable to see or in pain
Not all symptoms appear together. In some cases the pet may only have one!
What to do if you Suspect your Pet has Glaucoma?
Please bring your pet down to your regular vet immediately so they can assess the situation! Pets with glaucoma for >72 hours (sudden onset) can become permanently blind. Unfortunately, by the time most owners realise their pets have vision loss, it is irreversible.
What can your Vet do for you?
Your vet will use a tonometer to assess your pet’s IOP. If findings show that the IOP is more than 20mmHg, your pet will need to go on eyedrops to lower its eye pressure. Your vet will also be able to help you find out if there are any underlying causes that are behind this issue and treat it. Referral to an ophthalmologist may also be warranted if further investigation regarding special equipment is required.
Measures such as reducing stress and changing your pet from a collar to a harness can help bring down its IOP.
In some cases, despite medical therapy such as eye drops and oral pain relief, the eye pressure may not be able to be controlled which causes the pet discomfort and migraine-like headaches. During this time, your vet may recommend an enucleation surgery. Enucleation is the removal of the eyeball and then sealing the eyelids. Ophthalmologists are able to implant a fake eyeball (intraocular prosthesis) for owners who request it. Dogs and cats do very well with this surgery even though it sounds scary. The source of pain is gone and they are able to adapt well with one eye. There are some dogs, especially those with primary glaucoma, that require both eyes to be removed. Their quality of life should remain good as they can rely on their sense of smell and hearing to navigate.