Eye problems in dogs and cats: redness, ulcers, dry eye and glaucoma

A suddenly painful, red or cloudy eye, an enlarged-looking eye or a sudden change in vision can be a warning sign of glaucoma and needs prompt veterinary assessment.

Glaucoma raises pressure inside the eye, causing pain and damage to the retina and optic nerve that can rapidly become irreversible. The signs are not specific to glaucoma, so an eye examination and pressure measurement are needed to distinguish the cause. [1]

Squinting or holding an eye partly closed often means that the eye is painful, and a corneal ulcer is one important possible cause.

An ulcer may also cause tearing, mucoid discharge, redness or cloudiness on the eye surface. Because ulcers can worsen quickly and threaten sight, a newly painful or tightly closed eye needs prompt veterinary examination. [2]

Yes. Cloudiness can be one sign of glaucoma in a dog or cat, especially when it appears with redness, tearing, pain or loss of vision.

Cloudiness does not identify glaucoma by itself, but glaucoma can damage sight rapidly. A sudden cloudy or painful eye therefore needs prompt veterinary assessment, including measurement of pressure inside the eye and examination of the optic nerve. [1]

Yes. Glaucoma can make a dog or cat's eye red, so redness should not automatically be assumed to be simple conjunctivitis.

Glaucoma may also cause cloudiness, tearing, pain, an enlarged-looking eye or reduced vision. Because pressure-related damage can progress rapidly, this combination needs prompt veterinary assessment and measurement of pressure inside the eye. [1]

Glaucoma in dogs is classified as primary or secondary.

Primary glaucoma begins with an inherited problem in the eye's drainage system and concerns both eyes even when only one is affected at first. Secondary glaucoma develops because another disease or injury blocks fluid outflow and may be linked to inflammation, a displaced lens, an advanced cataract, an eye mass or trauma. [1]

Yes. Raised pressure in a cat's eye can damage the retina and optic nerve and may lead rapidly to irreversible blindness.

Glaucoma is also painful, but signs can be vague: redness, cloudiness, tearing, an enlarged eye or a change in vision. Measuring eye pressure and examining the optic nerve are central parts of assessment. [1]

A corneal ulcer is a break in the protective surface layer of the clear window at the front of a dog or cat's eye.

A shallow ulcer affects the surface cells, while a deeper ulcer extends into the supporting corneal tissue. Depth matters because deeper damage is more difficult to repair and poses a greater threat to the eye. [2]

A deep corneal ulcer can weaken the wall of a dog or cat's eye and may eventually cause the eye to rupture or perforate.

The surface appearance does not reliably show an owner how far an ulcer extends. Veterinary examination is needed to judge its depth, look for an underlying cause and decide whether specialist assessment is warranted. [2]

A veterinary team commonly checks for a corneal ulcer with fluorescein, a coloured stain that adheres where the protective surface cells are missing.

The damaged area fluoresces green under blue light, making a surface defect easier to see. The wider examination then assesses the ulcer's depth and looks for an anatomical problem or infection that could interfere with healing. [2]

Many corneal ulcers in dogs begin with surface trauma, such as a scratch, a foreign object, rough play or rubbing the eye.

Low tear production, inward-turning eyelids, abnormal eyelashes, chemicals and infection can also damage the cornea. When irritation continues, finding the underlying cause matters because the ulcer may not heal normally.

Chronic ear problems can also contribute when head shaking or facial rubbing causes superficial damage to the eye. [2]

A dog with a corneal ulcer often squints or keeps the painful eye closed, with tearing, mucoid discharge, redness or surface cloudiness.

Not every ulcer shows every sign, and a small surface defect may still be very painful. Fluorescein staining during an eye examination is used to confirm whether the protective corneal surface is missing. [2]

A dog's corneal ulcer can worsen when it is deep, infected or repeatedly irritated by an eyelid, eyelash, low tear film or another underlying problem.

Corneal damage can progress quickly and eventually threaten vision or the structure of the eye. Prompt re-examination lets the veterinary team check healing and decide whether more advanced assessment is needed. [2]

Yes. Inadequate tears leave a dog's corneal surface less lubricated and protected, which can contribute to corneal ulceration.

Tears nourish the cornea and help clear debris and infectious agents. When the tear film is deficient, irritation, bacterial conjunctivitis, pigmentation, scarring and impaired vision can develop alongside an ulcer. [5]

A cataract is an opaque area within the lens of a dog or cat's eye, where clouding can interfere with light reaching the retina.

Cataracts can be present from birth or develop with inflammation, metabolic disease, injury or ageing. The effect on sight depends largely on how much of the lens has become opaque. [3]

No. An older dog or cat can develop nuclear sclerosis, an age-related lens change that creates a blue-grey haze but usually causes little meaningful loss of sight.

Cataracts can look similar from the outside but are true lens opacities and may impair vision. A thorough eye examination can tell the two changes apart and check for inflammation or other complications. [3]

Conjunctivitis is inflammation of the thin membrane lining a dog's eyelids and covering the white part at the front of the eye.

This membrane helps protect the eye and contributes to tears and corneal healing. When inflamed, it can become red and swollen and may produce watery, mucoid or pus-like discharge. [4]

Conjunctivitis in a dog commonly causes redness, swelling around the cornea, eye discharge and mild discomfort.

Those visible changes do not reveal whether infection, irritation or another problem is responsible. A veterinary history and examination, sometimes supported by tear testing or conjunctival samples, are used to investigate the underlying cause. [4]

Conjunctivitis in dogs can be linked to infection, environmental irritation, allergy, a foreign object, dry eye or an eyelid-shape problem.

Because several different problems inflame the same membrane, the word conjunctivitis describes what the eye is doing rather than why it started. Identifying the underlying trigger is important when signs persist or return. [4]

Conjunctivitis in only one of a dog's eyes can be associated with a foreign object, inflammation around the tear drainage system or dry eye.

The one-sided pattern is a clue rather than a diagnosis. A veterinary history and examination, often including tear measurement and checks for foreign material or eyelid problems, help identify why the conjunctiva is inflamed. [4]

Conjunctivitis affecting both of a dog's eyes commonly occurs with viral or bacterial infection, although environmental irritants and allergens can also inflame the conjunctiva.

The both-eye pattern is a clue rather than a diagnosis because the visible appearance usually cannot identify the cause. The veterinary assessment uses the dog's history, physical examination and selected eye tests to investigate it. [4]

Not usually. The appearance of a dog's inflamed conjunctiva often cannot show which infection, irritant or underlying eye problem caused it.

The assessment may combine the dog's history and eye examination with tear measurement, corneal staining or a sample from the conjunctiva. The tests chosen depend on the pattern, severity and duration of the signs. [4]

Yes. Environmental irritants and allergens are recognised causes of conjunctivitis in dogs, and they may affect one or both eyes.

Similar redness and discharge can also come from infection, dry eye, a foreign object or an eyelid problem. Repeated or persistent episodes therefore need the underlying cause considered rather than being labelled as allergy from appearance alone. [4]

Dry eye, also called keratoconjunctivitis sicca or KCS, occurs when a dog's tear film is too small in quantity or poor in quality.

A healthy tear film lubricates and nourishes the cornea while helping remove debris and infectious material. When it is deficient, the exposed eye surface becomes irritated and vulnerable to further damage. [5]

Dry eye in a dog commonly causes painful, red eyes with thick, sticky or mucoid discharge, and it often affects both eyes.

The discharge can be mistaken for a simple infection, while chronic surface irritation may gradually cause pigment, blood vessels and scarring on the cornea. Tear testing helps identify the underlying tear-film problem. [5]

Yes. Ongoing dry eye can cause pigment, new blood vessels and scarring across a dog's cornea, which may eventually interfere with vision.

The poorly protected surface is also more vulnerable to ulcers and bacterial conjunctivitis. These complications explain why dry eye is more than a comfort problem and why regular reassessment is part of long-term care. [5]

A veterinary team can measure a dog's tear production with a Schirmer tear test, using a small paper strip placed at the eye.

The number is interpreted alongside the appearance of the cornea and tear film, the dog's signs and results from other eye tests. A normal tear quantity does not completely exclude poor tear quality. [5]

Yes. Dry eye in dogs commonly requires lifelong management and regular follow-up to maintain comfort, protect the cornea and monitor tear production.

The response can change over time, and surface damage may progress if control is lost. Follow-up examinations allow the veterinary team to check both tear-film function and complications such as ulceration, pigment or scarring. [5]

Conjunctivitis is inflammation of the thin membrane lining a cat's eyelids and covering the white part at the front of the eye.

It is common in cats and can arise from infection, irritation or another eye problem. The inflamed tissue often looks pink or red, becomes swollen and produces watery or thicker discharge. [6]

Conjunctivitis in a cat commonly causes redness, swollen conjunctival tissue, eye discharge and mild discomfort.

Those visible changes do not identify whether herpesvirus, bacteria, irritation or another problem is responsible. The veterinary assessment uses the cat's history, physical examination and selected tests to investigate the underlying cause. [6]

Conjunctivitis in cats is often linked to feline herpesvirus, but bacteria, foreign objects, environmental irritants and other eye problems can also cause it.

More than one factor can be present at once, particularly when a viral flare is followed by a secondary bacterial infection. The cause affects which general veterinary approach is appropriate. [6]

Conjunctivitis in only one of a cat's eyes can be associated with a foreign object, inflammation of the tear sac or dry eye.

Infectious conjunctivitis can also begin on one side before spreading, so laterality is only one clue. The cornea, eyelids, tear film and drainage system all need consideration when the problem remains one-sided. [6]

A cat's conjunctivitis can start in one eye and then involve both when a viral or bacterial infection is responsible.

The spread does not identify a particular organism, and environmental irritants or allergens can also cause conjunctivitis. Appearance alone is not enough, so the cat's history, examination and selected tests provide the wider clinical context. [6]

Not usually. The visible appearance of a cat's conjunctivitis often cannot show whether infection, irritation, dry eye or another problem is responsible.

The assessment can combine history and a full eye examination with tear testing, corneal staining or laboratory examination of conjunctival material. Results are interpreted alongside the pattern and severity of the cat's signs. [6]

Yes. After exposure to feline herpesvirus, virtually all cats remain persistently infected, and many later develop one or more episodes of recurrent disease.

A flare can affect the conjunctiva or cornea, causing conjunctivitis, corneal ulceration or keratitis. Because recurring eye disease is part of persistent infection, a new bout does not necessarily mean the cat was exposed again. [7]

Yes. Acute feline herpesvirus eye disease can cause conjunctivitis, corneal ulceration and keratitis, and it may be severe and painful.

A corneal ulcer is a break in the clear surface of the eye. Repeated herpesvirus flare-ups can also cause progressive corneal damage that may ultimately affect sight. [7]

Yes. Repeated bouts of feline herpesvirus eye disease can cause progressive damage to the cornea and may ultimately lead to blindness in an affected cat.

This does not mean every flare-up will damage vision. The risk comes from repeated disease affecting the clear corneal surface, so recurring eye problems are worth taking seriously. [7]

A cat with a corneal ulcer often squints or keeps the painful eye partly closed, with tearing, discharge, redness or a cloudy area on the eye surface.

The defect may not be obvious without fluorescein staining, while an ulcer can worsen quickly and threaten sight. These signs therefore warrant prompt veterinary examination even when the visible mark on the cornea looks small. [2]

Yes. Cats can develop dry eye when tear production is inadequate, although the condition is less common in cats than in dogs.

In cats, long-term feline herpesvirus infection is one recognised association. Too little tear fluid leaves the corneal surface less lubricated and less able to clear debris, which can sustain irritation. [8]

Dry eye can cause persistent conjunctivitis with thick discharge in a cat, as well as slow-healing corneal ulcers and scarring.

The problem begins with inadequate tear production, leaving the corneal surface less protected and less able to recover. A recurring discharge can therefore reflect a tear-film problem rather than a simple isolated infection. [8]