SYMPTOM
Squinting or holding eye closed
Partial or complete closure of one or both eyes, sometimes accompanied by visible discomfort or resistance to opening the affected eye.
Corneal injury or ulceration
Squinting is one of the hallmark responses to corneal pain. Even a superficial scratch on the corneal surface, which is among the most densely innervated tissues in the body, can produce pronounced blepharospasm. The degree of squinting often correlates with the severity of corneal involvement, though individual pain thresholds vary.
Conjunctivitis or ocular surface inflammation
Inflammation of the conjunctiva — the mucous membrane lining the eyelids and covering the white of the eye — can produce squinting alongside redness, discharge, and swelling. Causes range from allergic reactions and environmental irritants to viral and bacterial infections. The squinting may fluctuate with the degree of inflammation.
Uveitis (intraocular inflammation)
Inflammation within the eye itself can produce significant photophobia and squinting. Uveitis may develop secondary to infections, immune-mediated processes, trauma, or lens-related conditions. The pain is often deep and aching, producing persistent squinting that may worsen in bright light.
Glaucoma (elevated intraocular pressure)
Increased pressure within the eye can produce a dull, persistent pain that leads to squinting and reluctance to open the affected eye. The squinting may be accompanied by a dilated pupil, corneal cloudiness, or a visibly enlarged eye in chronic cases.
Foreign body
Plant material, sand, hair, or other debris trapped beneath the eyelids or embedded in the conjunctiva can produce persistent irritation and squinting. The animal may show sudden-onset squinting following outdoor activity, and the discomfort may be most pronounced immediately after the foreign body lodges.
Why timing matters
Early observation
Squinting that appears suddenly, particularly affecting only one eye, often indicates an acute event such as a corneal scratch, foreign body, or the onset of ocular inflammation. The sudden nature of the change distinguishes it from chronic conditions and may help localise the problem to a specific incident. Early squinting may be intermittent initially, worsening over hours as inflammation develops.
Later presentation
Persistent squinting over days suggests an ongoing source of ocular pain that has not resolved spontaneously. The eye may become increasingly inflamed, with developing redness, discharge, and possible corneal changes. Chronic squinting that waxes and wanes may indicate a recurring condition or a persistent irritant such as an aberrant eyelash or entropion.
The trajectory of squinting depends on its cause. Foreign body-related squinting may resolve once the material is removed. Corneal ulcers may produce squinting that improves as healing progresses or worsens if infection develops. Glaucoma-related squinting may fluctuate with pressure changes. Monitoring whether the squinting is improving, stable, or worsening provides important information about the trajectory of the underlying process.
Conditions commonly associated
Corneal Ulcers
Squinting is one of the earliest and most consistent signs of corneal ulceration, reflecting the intense pain produced by exposure of the densely innervated corneal stroma.
Glaucoma in Dogs
Squinting accompanies glaucoma as elevated intraocular pressure produces a deep, aching pain that leads to blepharospasm, particularly during acute pressure spikes.
Conjunctivitis
Ocular discomfort and light sensitivity in conjunctivitis often manifest as partial or complete eyelid closure.
Keratoconjunctivitis Sicca (Dry Eye)
The chronic irritation and discomfort from inadequate tear film in dry eye often leads dogs to squint or hold the affected eye partially closed.
Entropion
The discomfort from hair rubbing against the cornea causes characteristic squinting or blepharospasm.
Cherry Eye
Irritation from the prolapsed gland and any secondary conjunctivitis may cause squinting or discomfort.
Uveitis
Pain from intraocular inflammation causes the eye to be held partially or fully closed.
When to explore further
Sudden-onset squinting in one eye, particularly following outdoor activity or an encounter with another animal, may indicate a corneal injury or foreign body that could benefit from prompt examination.
Squinting accompanied by visible cloudiness or colour change in the eye, altered pupil size, or a visible change in the eye's shape or appearance suggests that the underlying process extends beyond mild surface irritation.
Squinting that persists beyond 24 hours without improvement, even if initially mild, may indicate that the cause is not self-limiting and the underlying process may benefit from characterisation.
Squinting accompanied by thick or coloured discharge from the eye may suggest secondary infection that could complicate the underlying cause of the ocular discomfort.
Noting which eye is affected, when the squinting began, and whether it is constant or intermittent provides useful baseline information. Observing whether the animal is also pawing at the eye, showing increased tearing, or displaying sensitivity to light can help build a more complete picture. Avoiding the temptation to force the eye open for examination is generally prudent, as this can increase discomfort and potentially worsen any underlying corneal injury.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS