SYMPTOM
Enlarged eye
Owners usually notice that one eye looks bigger or more bulging than the other, or that both eyes look larger or more staring than usual. The change may come with redness of the white of the eye, a cloudy or bluish cornea, squinting, watering, a protruding third eyelid, reluctance to open the mouth or chew, or signs of poor vision such as bumping into things. An eye can look enlarged because the eyeball itself has stretched, because something behind it is pushing it forward, because it has been forced out of its socket, or because the pupil is widely dilated, and these can look alike from the front.
Buphthalmos From Chronic Glaucoma
Long-standing elevation in intraocular pressure gradually stretches the collagen fibres of the globe, producing a genuinely larger eye rather than one displaced forward. It reflects pressure that has been raised for some time, and in dogs a visibly stretched eye has often already lost much or all of its vision. It is associated with the same breeds prone to primary glaucoma, including Cocker Spaniels and Basset Hounds, and with secondary glaucoma from causes such as lens luxation and uveitis. Corneal clouding and reddened vessels over the white of the eye are common. Firmness cannot be judged reliably by touch, and pressure is measured with a tonometer.
Orbital Space-Occupying Disease (Exophthalmos)
Disease behind the eye, such as a retrobulbar abscess, cellulitis, or a tumour, pushes a normal-sized globe forward within the orbit, which can look similar to true enlargement from the front. The third eyelid often protrudes, and opening the mouth can be painful because the jaw presses on the tissues behind the eye as it opens. Abscesses and cellulitis tend to develop over a few days with pain and swelling, whereas tumours more often cause slower, painless bulging, although the signs overlap and imaging such as CT is needed to tell them apart; in one referral study of dogs, about 60% of cases were tumours and about a third inflammation or infection. An eye pushed forward may not close fully, and the exposed cornea can ulcerate. Retrobulbar abscesses can follow a penetrating injury from a foreign body such as a grass awn or stick, or infection at the root of an upper back tooth, although often no cause is found.
Traumatic Globe Proptosis
The eyeball can be forced partly out of the orbit by a blow to the head, a fall, or restraint around the neck, with the eyelids then trapping it in that forward position. Brachycephalic breeds such as Pugs, Shih Tzus, and Boston Terriers have shallow orbits and prominent eyes, so this can occur with comparatively minor trauma, including firm handling or a scuffle with another dog. The exposed surface dries quickly and swelling behind the eye tightens the eyelids around it. The outlook for vision depends mainly on how badly the eye, the muscles around it and the optic nerve are injured, and is better when the pupil still responds to light. In dogs, fewer than half keep their vision, roughly a quarter to 40% in published reports, and very few do in cats, in which proptosis takes much greater force and often comes with facial fractures.
Breed-Related Globe Prominence
Some breeds, particularly brachycephalic types such as Pugs, Pekingese, and Boston Terriers, have naturally shallow orbits that leave a normal-sized eye looking proportionally larger and more prominent than in longer-nosed breeds. This is a conformational feature present from a young age rather than a change over time, and both eyes are usually affected equally, without redness, cloudiness or discomfort. It reflects normal anatomical variation rather than a change in the eye itself, although the same shallow orbits leave these eyes more exposed to proptosis and corneal ulcers.
Acute Glaucoma and Lens Luxation
A sudden rise in pressure inside the eye, from primary glaucoma or from secondary causes such as a lens that has slipped forward, inflammation inside the eye (uveitis), bleeding or a tumour, can make the eye look larger, red and cloudy or bluish, with a dilated pupil, squinting and watering. Cocker Spaniels, Basset Hounds, Beagles, Shih Tzus and Siberian Huskies are among the breeds predisposed to primary glaucoma, and terrier breeds to lens luxation. In cats, glaucoma is most often secondary to uveitis or tumours. Blindness can follow within hours to days of an acute rise.
Dilated Pupils From High Blood Pressure in Cats
In cats with high blood pressure, most often linked to chronic kidney disease or hyperthyroidism, retinal detachment and bleeding inside the eye can cause sudden blindness with widely and persistently dilated pupils. The eyes then look larger and darker although the eyeball is normal in size, and the retina can be damaged further while the pressure stays high.
Why timing matters
Early observation
An eye that has enlarged or bulged over hours or a few days carries the most time-sensitive possibilities. In acute glaucoma, raised pressure damages the retina and optic nerve and blindness can follow quickly. After a proptosis, the exposed eye dries and swelling behind it builds, and in published reports most dogs, and nearly all cats, lose sight in the affected eye. Pressure inside the eye cannot be judged by looking or by touch, and is measured with a tonometer.
Later presentation
An eye that has become visibly stretched (buphthalmos) usually reflects pressure that has been raised for some time, and in dogs much or all of the vision in that eye has often already been lost. Where the cause is primary glaucoma, the other eye may later be affected. A slowly bulging, painless eye can reflect a tumour behind it, and the longer an eye cannot close fully, the more exposed the cornea is to drying and ulceration.
How fast the change happened is one of the more useful features. A lifelong, symmetrical prominence of both eyes in a flat-faced breed is usually conformation. A change in one eye over hours to days, a red or painful eye, or a change after trauma points towards the possibilities in which delay affects vision or the eye itself. True enlargement, forward displacement and a dilated pupil can look alike from the front, and telling them apart relies on examination, pressure measurement and sometimes ultrasound or CT.
Conditions commonly associated
Glaucoma
Raised pressure inside the eye can make it look larger, red and cloudy, and pressure that stays high stretches the eyeball (buphthalmos). Vision can be lost within hours to days of an acute rise, so a visibly stretched eye often reflects pressure that has already caused lasting damage.
Feline Herpesvirus (FHV-1)
Feline herpesvirus infection can cause inflammation of the conjunctiva and other eye structures, leading to swelling of the conjunctiva and eyelids that can make the eye look enlarged, although the eyeball itself is normal in size. This ocular involvement often occurs alongside other upper respiratory signs such as sneezing and nasal discharge.
Hyperthyroidism in Cats
Some hyperthyroid cats also have high blood pressure, and it is the high blood pressure, not the overactive thyroid itself, that can detach the retina and leave the pupils widely dilated, so that the eyes look larger.
Chronic Kidney Disease in Cats
High blood pressure is common in cats with chronic kidney disease and can be present at any stage of it, not only when the kidney disease is advanced. The retinal detachment and dilated pupils that make the eyes look larger come from the high blood pressure rather than from the kidney disease itself.
Lens Luxation
When the lens slips forward it can block drainage of fluid from the eye, and pressure can rise quickly, making the eye red, cloudy and larger-looking. Terrier breeds are predisposed to primary lens luxation.
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Glaucoma in Dogs
Primary glaucoma in predisposed breeds such as Cocker Spaniels and Basset Hounds, and secondary glaucoma from lens luxation or uveitis, are the main causes of a truly enlarged eye in dogs.
Systemic Hypertension in Cats
High blood pressure in cats can cause retinal detachment and bleeding inside the eye, with sudden blindness and widely dilated pupils that make the eyes look larger. Chronic kidney disease and hyperthyroidism are the most frequent underlying causes.
Uveitis
Inflammation inside the eye can block fluid drainage and lead to secondary glaucoma. In cats, uveitis is the most frequent cause of glaucoma, and so of true enlargement of the eyeball.
Hyphaema
Bleeding inside the eye can block fluid drainage and raise the pressure, producing secondary glaucoma. It can follow trauma or reflect high blood pressure, clotting problems or a tumour.
Horner's Syndrome
Horner's syndrome makes the affected eye look smaller and sunken, with a small pupil and a raised third eyelid, so the normal eye on the other side can look enlarged by comparison.
When to explore further
When an eye looks larger over hours or a day or two, particularly with redness, a cloudy or bluish cornea, a widely dilated pupil or squinting, which is the typical picture of an acute rise in pressure inside the eye, where vision can be lost within hours to days
When the eye has been pushed partly out of its socket after a knock, a fight or pressure on the neck, so that the eyelids sit behind the eyeball, because the exposed surface dries and swelling builds behind the eye from the moment it happens
When a bulging eye comes with pain on opening the mouth, reluctance to chew, a protruding third eyelid, facial swelling or general dullness, which can reflect an abscess, inflammation or a tumour behind the eye
When a cat's pupils stay widely dilated in bright light or the cat seems suddenly unable to see, which can reflect retinal detachment or bleeding inside the eye from high blood pressure
When an eye that has always looked prominent in a flat-faced breed starts to look different from the other eye, or becomes red, cloudy or uncomfortable
When one eye has slowly come to sit further forward than the other over weeks, even without pain, or no longer closes fully, which can reflect a tumour or other mass behind the eye; an eye that does not close leaves the cornea open to drying and ulceration
Looking down at both eyes from directly above the head can show whether one sits further forward than the other. When the change was first seen, whether there was a knock or a fight, and whether the eye looks red, cloudy or painful are useful context for an examination. For an eye that has changed over hours or days, or has been pushed out of its socket, a period of observation adds little, because the pressure, the retina and the eye's blood supply cannot be assessed at home. Photographs taken in the same light over time are more informative for a symmetrical, lifelong prominence of both eyes in a flat-faced breed.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS