A bit of crust in the corner of the eye after a nap is common. Thick yellow or green discharge, a red eye, squinting or a cloudy eye are different. Eye problems in dogs can get worse quickly, and some threaten sight. The clear front of the eye has to stay transparent for a dog to see, and damage to it can be painful and can affect vision, so eye changes are worth acting on early. [1]
This guide explains the most common causes and the signs that mean you should call your vet today.
Signs that need a vet the same day
Call your vet promptly if your dog has:
- Squinting, holding an eye shut, or pawing at the eye (signs of pain)
- A cloudy or bluish eye, or a visible spot or dent on the clear surface of the eye
- A red eye with a dilated pupil, or an eye that looks bigger than the other
- Sudden changes in vision, such as bumping into things
- Any eye injury, such as a scratch or something stuck in the eye
- Thick yellow or green discharge
A red, painful eye with a wide pupil can be glaucoma, which can lead to pain and blindness if it is not treated quickly. Treat it as an emergency. [3]
Conjunctivitis (pink eye)
Conjunctivitis is inflammation of the thin pink membrane that lines the eyelids and covers the white of the eye. It is a sign, not a diagnosis: many different problems can inflame this tissue. [4] Typical signs are redness, puffy swelling of the tissue around the eye, itching or rubbing, watery eyes, and a discharge that can range from clear mucus to thick yellow-green. [4]
The cause matters more than the look of the eye. Before settling on a cause, vets rule out dry eye, corneal ulcers, eyelid and eyelash problems, irritating substances, foreign objects and problems inside the eye. [4] Allergies are one cause that is often missed: in dogs with skin allergies, the eyes can be affected too, and in one study every dog with allergic conjunctivitis had it in both eyes. [4] Because the causes differ so much, treating the discharge alone may not fix it if something else, such as a stuck object or an eyelid problem, is behind it.
Dry eye (KCS)
Dry eye, or keratoconjunctivitis sicca, happens when the eye does not make enough of the watery part of the tears. Dogs with dry eye typically have long-running conjunctivitis and a thick, mucus and pus-like discharge. [5] Over time it can cause discomfort, corneal ulcers and loss of vision. [5]
In most dogs, dry eye is driven by the immune system damaging the tear glands. [6] Treatment aims to calm that process and support tear production, and many dogs need it for the rest of their lives, because tear levels can drop again once treatment stops. [6] Because dry eye can look like an infection, a thick discharge that keeps coming back is worth a tear test at your vet.
Corneal ulcers and scratches
The cornea is the clear dome at the front of the eye. An ulcer is a break in its outer layer that exposes the tissue underneath. Ulcers can be very painful, and deep ones can lead to a hole in the eye or even loss of the eye. [1] A large study of dogs seen in general practice in England found that about 1 in 125 dogs had a corneal ulcer in a year, and pain was noted in close to half of them. [1]
Ulcers can follow injuries, but they also come from other eye problems: inward-rolling eyelids, abnormal lashes, dry eye, nerve problems that stop the eye closing, and some infections. A few dogs get slow-healing ulcers with no clear outside cause. [1] Flat-faced breeds were about 11 times as likely, and spaniel types about 3 times as likely, to have an ulcer as crossbreds in that study, with Pugs, Boxers and Shih Tzus most affected. [1] Your vet will treat the ulcer and look for its cause. Some dogs need surgery or referral to an eye specialist. [1]
Eyelid and eyelash problems
Sometimes the problem is hair or lashes rubbing the eye.
- Entropion is when the eyelid edge rolls inward so lashes and fur rub the eye. It is the most common eyelid shape problem in dogs and runs strongly in some breeds, such as the Shar-Pei and Chow Chow. [2] Watery eyes and squinting are common signs, and many affected dogs also have conjunctivitis or corneal ulcers. [2] Some cases are treated with surgery. [2]
- Ectropion is a loose, outward-turning eyelid edge. It is most often seen in large breeds with heavy facial skin, such as the Neapolitan Mastiff, Saint Bernard and Basset Hound. [2]
- Extra or misdirected eyelashes can rub the eye and cause corneal ulcers. [1][4] Your vet can check for them during an eye exam.
- Flat-faced breeds such as Bulldogs, Pugs and Shih Tzus often have prominent eyes and eyelids that may not close fully, which leaves the surface of the eye poorly protected and lubricated. Corneal ulcers were the most common problem in one study of these dogs. [7]
Cherry eye
Dogs have a third eyelid tucked in the inner corner of the eye, with a gland that makes a large share of the tears. In cherry eye, that gland pops out of place and shows as a red, fleshy lump in the inner corner. [8] It usually appears in young dogs, often before their first birthday, and is more common in breeds such as Cocker Spaniels, Beagles, Bulldogs, Boston Terriers and Pekingese. [8]
Cherry eye is usually not painful, but if it is left alone it can lead to irritation and inflammation. [8] Removing the gland has been linked to lower tear production and dry eye later, which is why vets prefer to put it back in place. [8]
Watery eyes from a blocked tear duct
Tears normally drain from the inner corner of the eye through a small duct into the nose. When that drainage does not work, tears can spill over onto the face. Your vet can check whether the duct is open with a simple dye test that shows whether the dye reaches the nose. [4]
Glaucoma: a red, painful eye that cannot wait
Glaucoma is a rise in pressure inside the eye that damages the retina and optic nerve. It is painful, it tends to get worse, and it can cause blindness. [3] The most common form in dogs is inherited and linked to how the eye’s drainage angle develops, and some breeds, such as the Basset Hound and American Cocker Spaniel, can have sudden attacks with a very inflamed eye. [3]
One sign vets look for is a dilated pupil that reacts slowly or not at all to light. [3] Pain often shows as a quiet, withdrawn dog rather than obvious squinting. Fast treatment to lower the pressure gives the best chance of saving the eye, so do not wait to see if it improves. [3]
What your vet may do
Depending on the signs, an eye exam may include: [4]
- Checking the eyelids, lashes and third eyelid, and looking for foreign objects
- A tear test (Schirmer tear test) for dry eye
- A dye test to show corneal ulcers and to check the tear ducts
- Measuring the pressure inside the eye for glaucoma
- A close look at the inside of the eye with special lights and lenses
At home, until you see your vet
- Stop your dog from rubbing or pawing at the eye. Ask your vet whether a protective cone would help.
- Do not use leftover eye drops or human eye medicines. The right medicine depends on the cause, so only use what your vet prescribes for this episode.
- Note which eye is affected, what the discharge looks like, and when it started.
FAQ
Is eye discharge in dogs always an infection?
No. Allergies, dry eye, corneal ulcers, eyelid and eyelash problems, irritants and foreign objects can all cause discharge. [4] Treating it as an infection may not help if the cause is something else.
Is dog conjunctivitis contagious?
It depends on the cause. Allergic conjunctivitis, dry eye or an eyelid problem are not contagious. If your vet suspects an infection, they can tell you whether to keep your dog away from other dogs.
Why does my dog’s eye discharge keep coming back?
Ongoing thick discharge can be a sign of dry eye, which usually needs long-term treatment. [5][6] Eyelid problems, misdirected lashes and allergies can also cause repeated problems. [2][4]
My dog is squinting. Is that serious?
Squinting usually means eye pain. Corneal ulcers and eyelid problems often cause squinting and watery eyes. [1][2] See your vet the same day.
What is the red lump near my dog’s lower eyelid?
In young dogs it is often cherry eye, a tear gland that has slipped out of place in the inner corner of the eye. Vets prefer to put it back rather than remove it. [8]
The bottom line
A little morning crust is usually nothing, but discharge with redness, squinting, cloudiness or pain is a reason to see your vet, often the same day. Many eye problems in dogs, from dry eye to corneal ulcers to glaucoma, respond best to early treatment, and the right treatment depends on finding the cause.
This article is for general information and is not a substitute for veterinary advice. If your dog has a red, painful, cloudy or discharging eye, please see your veterinarian promptly.
Sources
- O’Neill DG, et al. Corneal ulcerative disease in dogs under primary veterinary care in England: epidemiology and clinical management. Canine Genetics and Epidemiology, 2017 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC5471714/
- O’Neill DG, et al. Conformational eyelid disorders in dogs under primary veterinary care in the UK: epidemiology and clinical management. PLoS ONE, 2025 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12208470/
- Sebbag L, Pe’er O. Role of Inflammation in Canine Primary Glaucoma. Animals, 2023 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC10777923/
- Delgado E, et al. Diagnostic approach and grading scheme for canine allergic conjunctivitis. BMC Veterinary Research, 2023 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC9896716/
- Yogo T, et al. Tear Protein Alteration in Dogs with Keratoconjunctivitis Sicca. Animals, 2026 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12837657/
- Wei LN, et al. Topical applications of allogeneic adipose-derived mesenchymal stem cells ameliorate the canine keratoconjunctivitis sicca. BMC Veterinary Research, 2022 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC9185903/
- Costa J, et al. Clinical signs of brachycephalic ocular syndrome in 93 dogs. Irish Veterinary Journal, 2021 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC7836154/
- Zeng Y, et al. Genome-wide association studies with prolapsed gland of the third eyelid in dogs. Frontiers in Veterinary Science, 2024 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC11804112/