A little watery discharge after a windy walk may not seem alarming. However, eye problems can be difficult to judge at home, and an eye that looks mildly red can sometimes be painful or at risk of lasting damage.
Squinting, holding an eye closed, sudden redness, cloudiness or a change in vision should always be taken seriously. Some eye conditions progress rapidly, and early treatment can make the difference between a straightforward recovery and permanent damage to sight.
Here is how to recognise common warning signs and understand when your dog or cat needs veterinary help.
What does a healthy eye look like?
A healthy eye should usually be:
- open comfortably
- clear and bright
- free from marked redness
- similar in size and appearance to the other eye
- producing little or no discharge
- free from cloudiness, swelling or visible injury
A small amount of dry material at the inner corner of the eye can be normal in some pets, particularly after sleep. What matters is whether the discharge is new, increasing or accompanied by discomfort or changes in the eye itself.
Why might an eye become red or runny?
Redness and discharge are symptoms rather than diagnoses. Possible causes include:
- dust, pollen or mild irritation
- conjunctivitis
- a scratch or corneal ulcer
- a grass seed or other foreign material
- dry eye
- eyelid or eyelash abnormalities
- trauma
- infection
- inflammation inside the eye, known as uveitis
- glaucoma
- feline herpesvirus
- problems with tear drainage
- disease elsewhere in the body
Several of these conditions can look very similar to an owner. A veterinary eye examination may therefore include tear testing, fluorescein dye to check the cornea and measurement of pressure inside the eye.
Is clear discharge less worrying than yellow or green discharge?
The type of discharge provides useful information, but it does not tell the whole story.
Clear and watery:
Watery discharge may occur with wind, dust, allergies, blocked tear drainage or early irritation. It is also common when an eye is painful. A scratched cornea, for example, may cause marked tearing even when there is no pus.
White or stringy:
Sticky or stringy mucus can be associated with reduced tear production, inflammation or chronic irritation.
Yellow or green:
Thicker yellow or green discharge may occur with infection or significant inflammation. However, antibiotics are not automatically the correct treatment because the underlying cause could still be a corneal ulcer, dry eye, a foreign body, eyelid disease or a viral condition.
Blood or blood-tinged fluid:
Blood within or around the eye, or discharge following trauma, requires urgent veterinary attention.
Discharge should therefore always be considered alongside pain, redness, cloudiness, swelling and your pet’s general behaviour.
Squinting is a sign of pain
Squinting, repeated blinking or holding an eye closed is called blepharospasm. It is commonly a response to discomfort or pain.
Possible causes include:
- a corneal scratch or ulcer
- material trapped under an eyelid
- inflammation inside the eye
- glaucoma
- trauma
- an abnormal eyelash
- an inward-rolling eyelid
- severe conjunctivitis
A pet who is persistently squinting should not simply be monitored for several days. Corneal ulcers and other painful eye conditions may worsen quickly.
Veterinary literature identifies redness, cloudiness, discomfort, bulging and sudden vision loss as common presentations of ocular emergencies. Delayed treatment of a true emergency can result in permanent blindness or even loss of the eye.
What is a corneal ulcer?
The cornea is the transparent front surface of the eye. A corneal ulcer occurs when part of its protective outer layer is damaged.
Common causes include:
- scratches from plants, twigs or another animal
- grass seeds or grit
- rubbing the eye
- dry eye
- inward-rolling eyelids
- abnormal eyelashes
- poor eyelid closure
- feline herpesvirus
- abnormalities that affect normal corneal healing
Typical signs include squinting, excessive blinking, tearing, redness, rubbing at the face and sometimes cloudiness.
Many ulcers heal well when treated early. However, some become infected, deepen or begin to “melt” as corneal tissue breaks down. A deep ulcer may perforate the eye. If you suspect an ulcer, seek veterinary advice and support.
The Royal Veterinary College advises that corneal ulcers in dogs and cats commonly cause ocular discomfort, excessive blinking and tearing. Trauma from scratches, thorns and play is among the frequent causes.
Are some pets at greater risk?
Any pet can develop an eye problem, but some are particularly vulnerable.
Flat-faced dogs and cats
Breeds with prominent eyes, shortened muzzles or facial folds may have reduced protection of the eye surface, incomplete blinking, eyelid abnormalities or greater exposure to trauma.
A retrospective study of 347 dogs with corneal ulcers found associations between skull conformation and the type and complexity of ulceration. Brachycephalic dogs were more likely to experience complex corneal disease.
Owners of breeds such as French Bulldogs, Pugs, Shih Tzus, Boston Terriers, Persians and Exotic Shorthairs should be particularly alert to squinting, cloudiness or rubbing.
Pets with dry eye
Reduced tear production means the cornea is not properly lubricated or protected. Dry eye may cause redness, discomfort and thick, sticky discharge. Without treatment, it can lead to ulceration, scarring and impaired vision.
Cats with feline herpesvirus
Feline herpesvirus type 1 is a common cause of conjunctivitis and corneal disease in cats. It may produce redness, watery discharge, squinting and, in some cases, corneal ulcers.
The infection can remain latent in the body and reactivate, sometimes during periods of stress or illness. Ocular signs may affect one or both eyes.
Not every runny eye in a cat is caused by herpesvirus, so an examination is still needed before deciding on treatment.
When is a red eye an emergency?
Seek urgent veterinary care if your pet has any of the following:
- sudden or severe squinting
- cannot or will not open the eye
- a cloudy, blue, white or hazy appearance
- a visible scratch, wound or object
- known trauma to the eye or face
- blood in or around the eye
- one eye that appears larger, smaller, sunken or more prominent
- marked swelling
- unequal or asymmetric pupils
- a pupil that remains very large or very small
- sudden loss of vision
- bumping into objects or appearing disorientated
- the eye has come out of its socket
- a cut eyelid
- severe pain or distress
- chemical exposure
- rapidly worsening redness or discharge
Glaucoma, deep corneal ulcers, penetrating injuries, lens displacement and inflammation inside the eye can all threaten vision. Ophthalmic emergencies require rapid diagnosis and treatment to preserve sight and the eye itself.
Do not wait overnight with a suddenly cloudy, bulging, very painful or injured eye without first seeking veterinary advice.
What about mild redness or discharge?
Arrange a veterinary assessment if:
- redness lasts more than a few hours
- discharge keeps returning
- one eye is consistently more watery than the other
- your pet rubs at the eye
- the discharge becomes sticky, yellow or green
- the eyelids or surrounding skin become swollen
- the third eyelid is more visible than usual
- the eye looks different from the other one
- your pet has had previous eye problems
- symptoms are not clearly improving
Eye symptoms can change rapidly. Even when the problem initially seems mild, prompt assessment is safer than waiting several days.
What can you do before speaking to a vet?
Stop your pet rubbing the eye:
Rubbing can turn a small scratch into a deeper ulcer. Use a well-fitting protective collar if you have one and your pet tolerates it safely.
Keep your pet calm:
Avoid rough play, running through long grass or situations where the eye could be knocked again.
Gently clean around the eye:
You can wipe discharge from the surrounding fur using clean gauze or cotton wool dampened with sterile saline or cooled boiled water.
Use a fresh piece for each wipe and a separate piece for each eye. Do not scrub the surface of the eye.
Rinse after obvious loose debris:
When dust or fine debris has just entered the eye, gentle flushing with sterile saline may help while you seek advice. Do not try to remove anything that appears embedded or trapped beneath an eyelid.
Chemical exposure:
If a chemical, shampoo or irritant has entered the eye, begin flushing immediately with plenty of lukewarm water or sterile saline and contact a vet. Continue rinsing during the journey where practical.
Take the product packaging with you.
What should you avoid?
Do not:
- use human “red eye” drops
- use leftover antibiotic or steroid eye medication
- apply creams, tea, salt mixtures or home remedies
- use contact lens cleaning solution
- try to remove an embedded object
- place pressure on an injured or bulging eye
- give human painkillers unless specifically instructed by a vet
- wait several days when your pet is squinting
Steroid-containing eye drops can delay healing and may make some corneal ulcers considerably worse. This is one reason a fluorescein stain is often performed before particular eye medications are prescribed.
Old medication may also be contaminated, out of date or entirely inappropriate for the new problem.
What will the vet check?
A veterinary eye assessment may include:
Examination of the eye and eyelids:
The vet will check the eyelids, eyelashes, conjunctiva, cornea, pupils and internal structures where possible. They may also look beneath the eyelids for foreign material.
Fluorescein staining:
A harmless fluorescent dye highlights damage to the corneal surface and helps identify an ulcer.
Tear production:
A Schirmer tear test measures whether the eye is producing enough tears.
Eye pressure:
Tonometry measures pressure inside the eye. High pressure can indicate glaucoma, while low pressure may occur with inflammation inside the eye.
Vision and pupil responses:
The vet may assess whether your pet can see and whether the pupils respond normally to light.
Additional tests, imaging or referral to a veterinary ophthalmologist may be recommended for more complex conditions.
Can an online vet help?
Photos and video can be useful when assessing redness, discharge, swelling and your pet’s behaviour. An online veterinary consultation can help determine whether the signs appear urgent and whether your pet should be seen immediately or can safely wait for a routine appointment.
However, eye conditions often cannot be diagnosed fully from appearance alone. Fluorescein staining, tear testing, pressure measurement and close examination may be needed.
Online advice should therefore support triage, not delay an in-person examination when an eye is painful, cloudy, injured or changing rapidly.
Download the PawSquad app for advice and support with your pet’s eye condition.
The safest rule is to take eye pain seriously
Eyes are delicate, and different diseases can look remarkably similar. Conjunctivitis, a corneal ulcer, dry eye, glaucoma and uveitis may all cause redness and discharge, but they require very different treatment.
Squinting is particularly important because it usually indicates discomfort. A pet who is holding an eye closed, rubbing it, developing cloudiness or showing any change in vision should be assessed promptly.
Early veterinary advice protects comfort, improves the chance of successful treatment and may help save your pet’s sight.