What Is Glaucoma?
Glaucoma is one of the most serious eye conditions a dog can develop, and sadly, one of the most underrecognised in its early stages. It occurs when the pressure inside the eye — known as intraocular pressure — rises to levels that damage the optic nerve and retina. Without prompt intervention, this damage is irreversible, and the result is permanent vision loss or total blindness.
The eye continuously produces and drains a fluid called aqueous humour. When the drainage pathway — the iridocorneal angle — becomes obstructed or dysfunctional, fluid accumulates and intraocular pressure rises. The optic nerve and retinal cells are exquisitely sensitive to this increased pressure, and damage can begin within hours of a significant pressure spike.
Primary vs Secondary Glaucoma
Understanding the distinction between primary and secondary glaucoma is helpful when it comes to recognising risk in your own dog.
Primary glaucoma is inherited and results from an anatomical abnormality in the drainage angle. It is breed-associated and affects both eyes, though typically not simultaneously. Breeds with a notable predisposition include Basset Hounds, Cocker Spaniels, Chow Chows, Shar Peis, Siberian Huskies, Dalmatians, Bouvier des Flandres, and Great Danes. If your dog belongs to a predisposed breed, awareness of early signs is particularly important, and baseline intraocular pressure screening is worth discussing with your vet.
Secondary glaucoma develops as a consequence of another ocular condition. Uveitis (inflammation inside the eye), lens luxation (where the lens shifts out of position), intraocular tumours, and trauma are among the most common underlying causes. Secondary glaucoma can occur in any breed and at any age, which is why recognising the symptoms broadly matters for all dog owners.
Early Warning Signs to Watch For
This is where early detection genuinely makes the difference between preserved vision and blindness. The challenge with glaucoma is that the early signs are subtle enough that they are frequently attributed to minor irritation, tiredness, or something the dog walked into. By the time the signs become unmistakable, significant damage has often already occurred.
Signs that warrant urgent veterinary attention include:
- Redness of the whites of the eye, particularly a redness that appears deeper or more diffuse than typical conjunctival irritation
- Excessive tearing or watery discharge from one eye
- The affected eye appearing larger or more prominent than the other — a sign of significant pressure elevation causing the globe to expand
- Cloudiness or a bluish haze over the cornea, which may look similar to the sclerosis of normal ageing but appears more suddenly
- Sensitivity to light — your dog may squint, avoid bright areas, or hold the eye partially closed
- Pawing at or rubbing the affected eye
- Apparent lethargy, reduced appetite, or behavioural changes that might indicate pain — dogs are stoic and may not vocalise discomfort even when intraocular pressure is severely elevated
Vision changes are not always obvious in dogs. Because they adapt well to gradual vision loss and rely heavily on memory and other senses, owners often do not notice significant visual impairment until it is pronounced. This is why the physical signs listed above matter more as early indicators than apparent changes in vision.
Why Speed Is Everything
Acute angle-closure glaucoma — a sudden, severe pressure spike — constitutes a veterinary emergency. Studies in dogs suggest that when intraocular pressure rises to acutely damaging levels, retinal ganglion cell death can begin within 24 to 72 hours. This is not a condition where a wait-and-see approach is appropriate. If you notice any combination of the signs above, particularly in a breed known to be predisposed, seek veterinary attention on the same day.
Even in chronic, slowly progressing glaucoma, earlier diagnosis allows for treatment strategies that preserve more visual function. Dogs diagnosed and treated before significant optic nerve damage has occurred have considerably better outcomes than those treated after vision loss is already established.
Diagnosis and Pressure Measurement
Diagnosis is confirmed through tonometry — measurement of intraocular pressure using a handheld device called a tonometer. Normal intraocular pressure in dogs ranges from approximately 10 to 20 mmHg. Readings consistently above 25 mmHg are considered elevated, and readings above 30 mmHg in a symptomatic eye represent a genuinely urgent situation.
A full ophthalmic examination will also assess the drainage angle, the state of the optic nerve, and whether there are any underlying conditions contributing to the pressure rise. Referral to a veterinary ophthalmologist is often appropriate, particularly for cases involving primary glaucoma or complex secondary causes.
Treatment and Management
Treatment aims to reduce intraocular pressure, manage pain, and preserve remaining vision for as long as possible. Medical management typically involves topical eye drops that either reduce aqueous humour production or improve its drainage. Carbonic anhydrase inhibitors and prostaglandin analogues are among the most commonly used classes.
Surgical options exist for cases where medical management is insufficient or where the goal is long-term pressure control. These include laser procedures to reduce fluid production, cyclodestructive surgery, and in some cases placement of drainage implants. In eyes where vision is already lost and pain is ongoing, enucleation (removal of the eye) is sometimes the most humane option, and most dogs adapt very well following the procedure.
For dogs with primary glaucoma in one eye, prophylactic treatment of the fellow eye is standard practice, as the second eye is at significant risk of developing the condition within months to years.
Routine Checks for At-Risk Breeds
If your dog belongs to a predisposed breed, having baseline intraocular pressure measurements taken during routine vet visits gives you a reference point for what is normal for that individual. Subtle deviations from baseline can be meaningful even when absolute numbers fall within the general normal range. This simple, non-invasive check takes only moments and costs very little relative to the value of the information it provides.