What this means
Redness in an eye usually comes from one of two places. A red inner eyelid and white of the eye point at surface inflammation, which dust, wind, allergy, dryness or infection can all cause. Redness together with a cloudy look, a widened pupil and obvious pain points at something happening inside the eye, and that is the more serious sign.
At home it is worth separating one red eye from two. A single red eye more often has a local cause: a foreign body, a scratch, an eyelash growing in the wrong direction, or the shape of the eyelid. Both eyes together more often point at a broader cause, such as allergy or a shortage of tears.
Pain itself is an important sign. A squinting eye, objecting to it being touched, rubbing the face on furniture or the carpet, and heavy watering all say the eye hurts. A painful eye is not something to watch at home: damage to the surface can deepen quickly, and raised pressure inside the eye can harm sight within hours.
Never put in drops left over from a previous occasion, or meant for another animal. Some eye preparations are only safe when the surface of the eye is intact, and that is something established by examination.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Irritation of the eye's surface
Dust, sand, wind through a car window or shampoo causes redness and watering. The pattern is a sudden start that eases gradually.
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A shortage of tears
When the surface is not kept moist enough it reddens and thick, mucous discharge appears. Dogs often rub the eye, and the redness keeps returning.
About the condition: Dry eye (keratoconjunctivitis sicca) -
A scratch on the eye's surface
A twig, a cat's paw or rubbing leaves a painful, watering, squinting eye. This needs assessing quickly because the damage can deepen.
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Changes in eyelid or eyelash position
An eyelid rolled inwards, or lashes growing the wrong way, scrape the surface continuously. The redness and watering then keep coming back.
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Raised pressure inside the eye
The eye reddens, looks cloudy, the pupil may be widened, and the dog is clearly uncomfortable. This is an emergency because sight can be lost quickly.
About the condition: Glaucoma -
An allergic reaction
Allergy causes redness and itching in both eyes, with face rubbing. Itchy skin or ears often go with it.
About the condition: Allergies (food, skin and environmental)
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether one eye is red or both
- Whether the eye is squinting and your dog rubs it
- Whether there is discharge, and what it looks like
- Whether the eye looks cloudy
- Whether both pupils are the same size
- Whether your dog bumps into things in dim light
When to book a routine visit
Book a visit if the redness does not clear within a day, if it keeps returning, or if there is persistent discharge. If the eye is painful, squinting or cloudy, or sight has changed, go straight away — eye problems worsen faster than most.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Eye problems Eyes A dog's eyes can be affected by many different problems: faults of the eyelids and lashes, inflammation, injuries, corneal ulcers, clouding of the lens or diseases of the retina. Eyes are sensitive and some kinds of damage can get worse quickly and affect sight, so changes in the eyes are not something to wait out. If an eye suddenly turns red, seems painful or has been injured, the dog needs to see a vet immediately.
- Dry eye (keratoconjunctivitis sicca) Eyes Dry eye is a condition in which the tear glands make too few tears, so the cornea and the conjunctiva dry out and become inflamed. Without its protective tear film the eye becomes sore, and over time the cornea can darken, scar and lose its clarity. This can weaken eyesight, so changes are worth showing to a vet.
- Glaucoma Eyes Glaucoma is a condition in which the pressure inside the eye rises because fluid can no longer drain out of the eye as it should. The raised pressure presses on the retina and the optic nerve, so glaucoma is very painful and can quickly take away sight. It is an emergency: the dog needs a vet immediately.
- Entropion Eyes Entropion is a condition in which the edge of the eyelid rolls inwards, so the eyelashes and eyelid hair rub against the surface of the eye. The constant rubbing irritates and hurts the eye and can damage the cornea, leading to ulcers. It can be inherited and show up in young dogs, and it sometimes develops later because of other changes to the eye or eyelids.
- Cherry eye Eyes This is a condition in which the tear gland of the third eyelid slips out of place and bulges from the inner corner of the eye as a red lump that looks like a cherry. The gland produces part of the tears, so if it stays out for long it can dry out, swell and keep the eye less moist. Although it looks alarming, it is not a major source of pain, but the eye is worth showing to a vet.
- Distichiasis Eyes Distichiasis is a condition in which extra eyelashes grow from the edge of the eyelid, where no lashes should be. Soft lashes may barely bother the eye, but stiffer ones rub against its surface. Constant rubbing irritates the eye and can damage the cornea, so whether the lashes are causing harm is for a vet to judge.
- Pannus (chronic superficial keratitis) Eyes This is an immune-related inflammation of the cornea: pinkish tissue that later darkens creeps slowly from the edge across the clear surface of the eye, like a cloud across a window. It develops slowly and may not hurt at all, so it is easy to miss, but over time it can impair vision. Only a vet can diagnose it and follow how it progresses.
- Conjunctivitis Eyes Conjunctivitis is inflammation of the conjunctiva, the thin pink membrane that lines the inside of the eyelids and covers the white of the eye. It can be caused by dust and other irritants, allergy, infection, dry eye or faults of the eyelids or lashes, and sometimes it is part of a general illness; what caused the inflammation is for a vet to work out.
Body systems: Eyes