An eye that becomes suddenly red, cloudy, enlarged or painful is an emergency rather than something to watch overnight. Glaucoma is a build-up of pressure inside the eye, and vision can be lost within hours of the pressure rising. Squinting, tearing, a hazy blue-grey surface or an eye held shut all warrant a same-day call.
Why eyes are different from most problems
With many conditions, a night of observation costs little. Eyes are the exception. The tissues that carry vision do not tolerate raised pressure, and once they are damaged the loss is generally permanent. That makes this one of the few situations where the difference between calling this evening and calling tomorrow morning genuinely changes the outcome.
The other complication is that a painful eye rarely looks dramatic. Owners expect an emergency to announce itself. A dog with glaucoma may simply be quiet, off their food, reluctant to be touched around the head, and blinking a little more than usual on one side.
What glaucoma actually is
The eye continuously produces a clear fluid that fills the front chamber and drains away through a filter at the angle where the iris meets the cornea. Production and drainage are normally in balance. When drainage is obstructed, fluid keeps arriving with nowhere to go, and the pressure inside the eye climbs.
That pressure presses on the optic nerve and the retina, the structures responsible for sight. It is also genuinely painful, comparable to a severe headache that does not let up. Because dogs and cats do not tell us about headaches, that part is almost always underestimated.
What owners actually notice
- Redness across the white of the eye, often with visible enlarged vessels
- A cloudy, hazy or bluish appearance to the clear front surface
- Squinting, excessive blinking, or an eye held partly or fully closed
- Tearing or discharge
- A pupil that stays large and does not respond to light, or pupils of different sizes
- An eye that looks bigger or more prominent than the other
- Rubbing the face on furniture or pawing at the eye
- Bumping into things, hesitating on stairs, or reluctance to move in dim light
- Being withdrawn, off food, or sensitive about the head being touched
Compare the two eyes in good light, from the front and from above. Differences in size, colour and pupil are easier to see side by side than one at a time. A photograph in daylight is helpful to bring with you.
Two kinds, and why the distinction matters
Primary glaucoma arises from an inherited abnormality in the drainage angle. It typically shows up in middle age, affects one eye first, and carries a high likelihood of the second eye becoming affected later. Recognised predisposed breeds include Cocker Spaniels, Basset Hounds, Beagles, Shar Peis, Chow Chows, Siberian Huskies and several terriers.
Secondary glaucoma develops because something else in the eye has blocked drainage. Inflammation inside the eye, a lens that has shifted position, bleeding after trauma, advanced cataracts or a growth can all do it. Cats are far more likely to have the secondary form, and in cats chronic inflammation inside the eye is the usual driver.
The distinction matters because secondary glaucoma means there is a second condition to find and address, and because primary glaucoma changes how the unaffected eye is monitored from that day forward.
The other eye deserves attention too
This is the part most owners are not told. In primary glaucoma, the fellow eye is at substantial risk of developing the same problem in the months and years that follow. Your veterinarian may recommend monitoring it, and in some cases preventive treatment, well before it shows any signs at all.
If your dog has been diagnosed in one eye, keep the recheck appointments even when the remaining eye looks perfect. That is the appointment that protects the vision your pet still has.
What happens when you come in
Assessment includes measuring the pressure inside the eye, which is a quick and well tolerated test, along with a full examination of both eyes to look at the cornea, the front chamber, the lens and, where the view allows, the back of the eye. Staining the surface checks for ulceration, since a painful red eye has several possible causes and they are managed differently.
Where the cause may sit behind the eye or elsewhere in the body, further testing through our diagnostic services may be recommended. Immediate treatment focuses on lowering the pressure and controlling pain, and that is handled through our urgent care service. Ongoing management, referral where specialist care is appropriate, and monitoring of the second eye sit within our medical services. Where surgery becomes part of the plan, our surgical team is involved in that discussion.
If this happens outside our opening hours, do not wait for us to open. Contact your nearest emergency veterinary hospital that night. Our checklist on preparing for an emergency veterinary visit is worth reading before you ever need it.
What not to do at home
Do not put anything into the eye. Human eye drops, contact lens solution, leftover medication from a previous problem or from another pet, and home rinses can all make matters worse, and some will actively interfere with the examination. Medication prescribed for a different eye condition can be genuinely harmful in glaucoma.
Do not let your pet rub the eye. A soft collar or an inflatable one keeps paws away on the drive in. Do not press on the eye or try to open it wide for a better look. Keep the lights low if your pet is squinting, and skip the walk until you have been seen.
Beyond dogs and cats
Eye problems in rabbits and small pets follow different rules and can reflect dental disease, respiratory infection or trauma rather than pressure changes. Any small pet with a closed, weeping, cloudy or bulging eye should be seen promptly, since these species deteriorate quickly and hide discomfort even more effectively than cats.
Older pets of any species benefit from having their eyes looked at as a routine part of a check-up, which is covered in our guide to senior pet care. Our overview of emergency signs every Surrey owner should know puts eye problems in the context of the wider list.
Frequently asked questions
How quickly can a dog lose vision from glaucoma?
Vision can be lost within hours of the pressure rising, which is why this is treated as an emergency rather than a next-day appointment. The longer the pressure stays high, the less likely sight is to be preserved. If you notice a suddenly red, cloudy or painful eye in the evening, contact an emergency hospital rather than waiting for morning.
Is glaucoma painful for dogs and cats?
Yes, and it is usually more painful than it looks. The discomfort is often compared to a severe, unrelenting headache. Because pets rarely cry out, the signs are subtle: withdrawal, reduced appetite, reluctance to be touched around the head, sleeping more, and a general flatness that owners often put down to age.
Can I use human eye drops until I can get an appointment?
No. Human eye drops, contact lens solutions and leftover medications can worsen the underlying problem and can interfere with the examination that follows. Some preparations used for other eye conditions are actively harmful when pressure is raised. Leave the eye alone, prevent rubbing, and get advice the same day.
Will my dog need the eye removed?
Not necessarily, and that decision depends on whether pressure can be controlled and whether the eye is still comfortable and sighted. Where an eye is permanently blind and painful despite treatment, removal is sometimes recommended, and pets typically adapt well and are visibly more comfortable afterward. Your veterinarian will discuss the options for your individual pet.
My dog’s other eye looks fine. Does it need checking?
Yes, particularly with the inherited form. The second eye carries a meaningful risk of developing the same problem later, and monitoring it, sometimes with preventive treatment, is a standard part of the plan. Keep those recheck appointments even when that eye appears completely normal.
What else causes a red eye that is not glaucoma?
Several things, including conjunctivitis, corneal ulcers, inflammation inside the eye, foreign material under the eyelid, dry eye and injury. They look similar from the outside but are managed very differently, and some treatments for one are harmful in another. That is exactly why a red painful eye needs examining rather than guessing.