Squinting (blepharospasm) in Horses

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Last updated on
4 min read

Key takeaways

Squinting or excessive blinking is the motion or position of the eyelid over the eye to protect against pain or irritation. In horses causes of pain or irritation to the eye include injuries, infections, and environmental irritants.

  • The majority of equine cases are caused by uveitis or corneal ulcers
  • Symptoms often observed alongside squinting or blinking include excessive tearing, swelling, cloudiness, or redness of the eye, and constriction of the pupil
  • Horses that blink or squint excessively other than when exposed to bright lights require emergency veterinary attention as many of the causes of this symptom result in blindness if not treated promptly
  • Diagnosis is based on physical and ophthalmic examination
  • Treatment depends on diagnosis, ranging from eye drops or ointments to surgery or even surgical removal of the eyeball
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A closer look: Squinting (blepharospasm) in Horses

Horses' eyes are sensitive and their eyesight is important to many of the roles they play. Excessive blinking and squinting that is not caused by bright lights are signs that the horse’s eyes are irritated or painful. Irritation or pain of the eyes is a veterinary emergency because some of the underlying causes of this symptom lead to blindness if left untreated.

Blinking and squinting vary in severity based on onset, the symptoms that accompany it, and whether it affects one eye or both.

The onset of blinking is sometimes sudden, such as in the case of injury to the eye. In other cases it is gradual, such as with glaucoma. In some cases, excessive blinking develops and then seems to resolve itself only to return at a later time, such as with recurrent uveitis.

The severity of blinking or squinting depends also on the other symptoms that accompany it. Some accompanying symptoms are localized to the eyes such as redness, cloudiness of the eye, and excessive tearing. In some cases, horses show symptoms affecting their entire body, such as fever. Horses with systemic symptoms often have a more severe disease than those with only local symptoms.

Possible causes

There are a wide variety of possible underlying causes of blinking.

Risk factors

Some underlying causes result in irritation in one eye, and some in both. Although it is possible for the horse to squint one eye, it is more likely that blinking or squinting happens in both eyes even when only one eye is affected. However, local accompanying symptoms (redness, swelling, cloudiness, etc) sometimes indicate whether one or both eyes are affected.

Testing and diagnosis

Diagnosis is based on physical examination and ophthalmic examination including:

  • Fluorescein stain tests
  • Swabs and scrapings to culture for infectious agents
  • Ultrasound of the eye

Treatment depends on the diagnosis. Common treatments include:

  • Antibiotics
  • Antifungals
  • Antiparasitic medications
  • Anti-inflammatories
  • Pain relief

Less commonly, referral to an ophthalmologist is necessary. Possible treatments include:

  • Surgery
  • Enucleation (removal of the eyeball)

Horses undergoing treatment for eye complaints often require protection from the sun. Sun visors or fly masks, particularly UV-protective versions, are suitable.

Similar symptoms

Healthy horses vary in how often they blink, with one horse blinking more often than another, or the same horse blinking more often than usual in dry weather or wind. Healthy horses also blink or squint when in bright light. It is possible to mistake normal blinking and squinting for excessive blinking and squinting.

Associated symptoms


No Author - Writing for Horse Side Vet Guide
Kaela Schraer, DVM - Writing for PetMD
Kaela Schraer, DVM - Writing for PetMD

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