CONDITION
Glaucoma in Dogs
Why this matters now
Glaucoma in dogs can present at any age but is most commonly recognised in middle-aged to older dogs. Primary glaucoma — caused by inherited anatomical abnormalities in the drainage angle of the eye — tends to present in breeds with known predispositions, often affecting one eye initially before the second eye becomes involved weeks to years later. Secondary glaucoma, which develops as a consequence of other ocular disease such as uveitis, lens luxation, or intraocular tumours, can occur in any breed at any age. The condition can develop acutely, with a dramatic rise in intraocular pressure over hours, or may build insidiously over weeks to months in chronic forms.
The trajectory of glaucoma depends on whether it presents acutely or chronically and how rapidly the elevated pressure is addressed. Acute glaucoma produces a sudden, significant rise in intraocular pressure that can cause irreversible damage to the retina and optic nerve within hours to days. The retinal ganglion cells and their axons, which form the optic nerve, are particularly vulnerable to pressure-induced ischaemia. Chronic glaucoma may produce more gradual damage, with progressive vision loss occurring over weeks to months as the sustained pressure gradually compromises retinal function. In many cases, particularly with primary glaucoma, the second eye is considered at high risk of developing the condition, and prophylactic management may be discussed. Advanced glaucoma can lead to buphthalmos — physical enlargement of the globe — as the sustained pressure stretches the scleral wall.
Signals & patterns
Early signals
Subtle redness of the eye
Episcleral congestion — dilation of the blood vessels on the white of the eye — can produce a diffuse redness that may be distinguished from conjunctivitis by the pattern and depth of vessel involvement. This may be intermittent if pressure fluctuates.
Mild squinting or discomfort
Dogs may show intermittent blepharospasm or reluctance to have the area around the eye touched. The discomfort may be subtle, with the dog appearing to squint more in bright light or holding the affected eye slightly narrower than normal.
Slight corneal cloudiness
Early corneal oedema from elevated intraocular pressure may produce a faint bluish haze over the corneal surface. This may be most noticeable in certain lighting conditions and can fluctuate if pressure is intermittently elevated.
Subtle behavioural changes
Dogs in the early stages may show decreased activity, reduced appetite, or seem quieter than usual. These non-specific signs are often attributed to other causes, making early glaucoma easily overlooked without specific ophthalmic evaluation.
Later signals
Obvious corneal oedema
A dense bluish-white cloudiness over the entire corneal surface indicates significant oedema from sustained pressure elevation. The cornea may appear uniformly hazy, obscuring the view of the iris and pupil.
Fixed, dilated pupil
Elevated intraocular pressure can paralyse the iris sphincter muscle, producing a pupil that is dilated and unresponsive to light. This mydriasis may be the first change noticed by owners, particularly if it produces asymmetry between the two eyes.
Visibly enlarged eye
Chronic elevation of intraocular pressure can stretch the sclera, producing buphthalmos — a visibly enlarged globe. The eye may appear to protrude more than the other and the eyelids may not close completely over the enlarged surface.
Evidence of vision loss
Dogs may bump into objects on the affected side, show reduced confidence in unfamiliar environments, or fail to track visual stimuli. Vision loss may be particularly noticeable in dim lighting if the retinal damage has progressed significantly.
Click to read about the biological mechanisms
How this is usually investigated
Investigating glaucoma centres on measuring intraocular pressure and assessing the structures within the eye that regulate aqueous humour dynamics, as well as evaluating the degree of damage to pressure-sensitive tissues.
Tonometry
Gonioscopy
Ophthalmoscopy
Ocular ultrasound
Electroretinography (ERG)
Options & trade-offs
Management of glaucoma in dogs aims to reduce intraocular pressure to a level that preserves retinal and optic nerve function while maintaining comfort. The approach depends on whether the eye retains visual potential, whether the glaucoma is primary or secondary, and the individual's response to initial treatment.
Topical pressure-lowering medications
Various eye drops can reduce intraocular pressure by either decreasing aqueous humour production or improving its outflow. Classes include prostaglandin analogues, carbonic anhydrase inhibitors, beta-blockers, and combinations thereof. Multiple drops may be used concurrently to achieve adequate pressure reduction.
Trade-offs: Long-term topical therapy requires consistent, often frequent administration which demands significant owner commitment. Some medications cause local side effects such as miosis (pupil constriction), conjunctival hyperaemia, or discomfort on application. The effectiveness of medical management alone often diminishes over time, particularly in primary glaucoma, as the underlying drainage abnormality persists.
Systemic pressure-lowering medications
Intravenous mannitol or oral carbonic anhydrase inhibitors may be used in acute glaucoma crises to rapidly reduce intraocular pressure while other treatments are initiated.
Trade-offs: Systemic medications can have broader side effects including increased urination, electrolyte changes, and gastrointestinal disturbance. Mannitol requires intravenous administration in a clinical setting and provides only temporary pressure reduction. These are typically bridge therapies rather than long-term solutions.
Laser cyclophotocoagulation
A laser is used to selectively destroy a portion of the ciliary body tissue that produces aqueous humour, reducing the overall rate of fluid production within the eye. This can be performed using transscleral or endoscopic approaches.
Trade-offs: The degree of pressure reduction is variable and difficult to predict precisely, as the amount of ciliary body tissue that needs to be treated varies between individuals. Over-treatment can lead to chronic low pressure (phthisis), while under-treatment may require repeat procedures. The procedure typically requires general anaesthesia.
Gonioimplant (drainage device)
A small tube or shunt is surgically placed to provide an alternative drainage pathway for aqueous humour, bypassing the dysfunctional natural drainage angle.
Trade-offs: These devices require specialist surgical placement and can be associated with complications including tube obstruction, implant migration, or excessive drainage. Long-term success rates vary, and the devices may eventually require revision or the addition of medical therapy.
Enucleation or intrascleral prosthesis
When an eye is irreversibly blind and painful, removal of the eye (enucleation) or placement of a cosmetic intrascleral prosthesis may be considered to eliminate ongoing pain. The prosthesis maintains the external appearance of an eye within the scleral shell.
Trade-offs: Enucleation is a definitive solution for pain but involves adapting to the altered appearance. An intrascleral prosthesis preserves cosmetic appearance but requires that the outer shell of the eye is healthy. Both options eliminate the need for ongoing glaucoma medication in the affected eye. Dogs typically adapt well to monocular vision.
Common misconceptions
"Glaucoma in dogs is the same as glaucoma in humans"
While both involve elevated intraocular pressure, canine glaucoma differs significantly from the most common form of human glaucoma. Human open-angle glaucoma typically progresses very slowly over years, while primary glaucoma in dogs often involves closed-angle or narrow-angle mechanisms that can produce rapid, dramatic pressure elevations. The acute presentation seen in many dogs is rare in humans. Additionally, canine glaucoma tends to be more aggressive and harder to control medically, with a higher proportion of cases eventually requiring surgical intervention or enucleation.
"If the eye looks normal, there cannot be a serious pressure problem"
Intraocular pressure can be significantly elevated before visible external changes develop. Early glaucoma may produce only subtle signs such as slight episcleral injection or mild corneal haze that are difficult to detect without specific examination. By the time dramatic changes like obvious corneal oedema, a dilated pupil, or buphthalmos are visible, substantial and often irreversible retinal damage may have already occurred. This is why tonometry — actual measurement of eye pressure — is essential for diagnosis.
"Once pressure is controlled, the eye is safe"
Controlling intraocular pressure is essential but does not eliminate the underlying cause in primary glaucoma. The inherited drainage angle abnormality persists, meaning that pressure can escape control as the disease progresses or treatment effectiveness wanes. Many dogs with primary glaucoma require escalating treatment over time, and a significant proportion will eventually lose functional vision despite management. The emphasis on pressure control is about slowing the rate of damage and maintaining comfort, not necessarily curing the condition.
Glaucoma represents a condition where the relationship between timing and outcome is particularly significant. The retinal ganglion cells that mediate vision are highly sensitive to pressure-induced damage and cannot regenerate once lost, making the window for effective intervention narrower than with many other conditions. For breeds known to carry predispositions, awareness of the early signs and the potential for bilateral involvement can be valuable. Understanding that glaucoma management is often a long-term endeavour, requiring ongoing monitoring and treatment adjustment, helps set realistic expectations for the trajectory of the condition.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS