Bit & Bridle

Equine Cataracts

Other Names

  • Cataract
  • Lens opacity
  • Nuclear sclerosis (age-related lens change, distinct from true cataract)

What are Cataracts in Horses?

A cataract is a clouding or opacity of the crystalline lens inside the eye, which impairs the normal passage of light to the retina and reduces visual clarity. In horses, cataracts can affect one or both eyes and range from small incidental opacities that cause no functional impairment to dense, complete opacities that result in significant or total blindness in the affected eye.

Cataracts can be congenital (present at birth) or acquired (developing over time). They are a recognised complication of equine recurrent uveitis (ERU), the most common cause of blindness in horses worldwide, making early eye examination important in horses with any history of uveitis. Cataracts can also occur secondary to injury, other inflammatory conditions, or as an age-related change.

For context on related eye conditions, see our entry on Equine Keratitis.

Causes

Several factors can lead to cataract development in horses:

  • Equine recurrent uveitis (ERU) — repeated inflammatory episodes within the eye cause protein deposition in the lens, the most common acquired cause of cataracts in adult horses
  • Congenital factors — some foals are born with cataracts, which may be associated with nutritional deficiencies in the dam during pregnancy, genetic predisposition, or developmental anomalies
  • Trauma — blunt or penetrating injury to the eye can disrupt the lens capsule or lens proteins, triggering cataract formation
  • Genetic predisposition — certain breeds, including the Morgan horse, appear to have a higher incidence of congenital cataracts
  • Age-related lens changes — true senile cataracts are less common in horses than nuclear sclerosis (a normal age-related haziness that does not impair vision significantly), but can occur in older animals
  • Metabolic and nutritional factors — less well characterised in horses than in some other species, but deficiencies during critical periods of lens development may play a role

Symptoms and Signs

Signs vary depending on the location, density, and extent of the opacity:

  • Visible whitish, grey, or bluish cloudiness in the pupil area when viewed in good light
  • Reduced visual acuity — the horse may stumble, bump into objects, or be reluctant to enter dark areas
  • Spookiness or behavioural changes, particularly in low-light conditions or when approaching from the affected side
  • Reluctance to move forward or hesitation at transitions
  • Squinting (blepharospasm), tearing, or sensitivity to light if uveitis is the underlying cause
  • Asymmetric pupillary light response — the affected eye may react differently to light than the unaffected eye

Small, incidental cataracts may be completely asymptomatic and discovered only on routine ophthalmic examination. Horses are remarkably adaptable to unilateral vision loss and may compensate well for many years.

Diagnosis

Ocular examination should be performed by a veterinarian experienced in equine ophthalmology, ideally with pharmacological mydriasis (pupil dilation using tropicamide) to allow full visualisation of the lens:

  • Direct and indirect ophthalmoscopy — allows visualisation of the lens and assessment of the retina and optic disc
  • Slit-lamp biomicroscopy — provides detailed imaging of the anterior segment, including the lens, and is the most informative method for characterising cataract type and location
  • Electroretinography (ERG) — assesses retinal function, essential before cataract surgery to confirm the retina is functioning and surgery would restore useful vision
  • Ocular ultrasound — used when the cataract prevents direct fundus examination, to assess for retinal detachment or other posterior segment pathology

Distinguishing true cataract from nuclear sclerosis is important — nuclear sclerosis presents as a bilateral, diffuse haziness that does not significantly impair vision and requires no treatment. A vet can differentiate these on examination.

Treatment

The only definitive treatment for a visually significant cataract is surgical removal:

  • Phacoemulsification — the technique of choice in horses. The cataractous lens is emulsified using ultrasonic energy delivered through a small incision and aspirated out of the eye. An artificial intraocular lens may be implanted to replace the natural lens. Results are best in young horses with congenital cataracts and intact retinal function.
  • Extracapsular lens extraction — an older technique where the lens is removed manually through a larger incision. Less common in equine practice now that phacoemulsification is widely available at specialist centres.
  • Medical management of underlying uveitis — if ERU is driving cataract progression, controlling inflammation is essential to slow further damage. This may include topical corticosteroids, systemic NSAIDs, and in some cases the surgical implantation of a sustained-release cyclosporine device.

Small, non-progressive, asymptomatic cataracts may be monitored without immediate surgical intervention. Regular ophthalmic examinations every six to twelve months help track progression. For guidance on equine ophthalmology specialists in the UK, the BEVA website at beva.org.uk provides a referral directory.

Prevention

Not all cataracts can be prevented, but the following steps help reduce risk and enable early detection:

  • Schedule annual ophthalmic examinations for all horses, particularly those with a history of eye disease or uveitis
  • Manage equine recurrent uveitis aggressively — controlling inflammation is the most important modifiable risk factor
  • Use UV-protective fly masks, particularly in horses with known eye sensitivity or high UV environments
  • Ensure adequate nutritional status in broodmares to reduce risk of congenital cataracts in foals
  • Have all foals examined ophthalmically within the first few days of life, especially in breeds with known predisposition

Prognosis

Prognosis depends on the type, extent, and cause of the cataract, as well as retinal integrity. Congenital cataracts in young foals treated with phacoemulsification carry a reasonably good prognosis for useful vision restoration, particularly if surgery is performed before vision deprivation has caused irreversible neurological changes. Cataracts secondary to recurrent uveitis carry a more guarded prognosis, as the underlying inflammatory condition may continue to damage other ocular structures even after cataract removal. Horses with complete cataract-related blindness in one eye often adapt remarkably well and can remain in work, but bilateral blindness significantly limits the horse’s future.

When to Call the Vet

  • You notice cloudiness, whiteness, or opacity in your horse’s eye
  • Your horse begins showing signs of vision impairment — stumbling, shying from one side, or reluctance to move into dim areas
  • There are signs of eye discomfort such as squinting, tearing, or light sensitivity
  • Your horse has a known history of uveitis and you wish to monitor for cataract development
  • You have a young foal and want a baseline ophthalmic examination

Frequently Asked Questions

Are cataracts in foals different from those in adult horses?

Yes, in important ways. Congenital cataracts in foals tend to be more surgically amenable than acquired cataracts in adults, particularly when intervention is early. However, there is a narrow window — delaying surgery in young foals risks amblyopia (failure of visual pathway development due to visual deprivation). Foals with dense cataracts should be assessed for surgery as early as possible, typically within the first few months of life.

Can a horse live a normal life with a cataract?

Many horses manage very well with a unilateral cataract, particularly if the affected eye still has some light perception. Horses are prey animals and highly attuned to visual threats; they typically adjust their behaviour to compensate for partial or unilateral vision loss. Bilateral cataracts are more limiting and significantly affect safety for both horse and handler.

Is cataract surgery available for horses?

Yes, phacoemulsification is available at specialist equine ophthalmology centres in the UK and internationally. It is performed under general anaesthesia and requires experienced ophthalmic surgeons. Outcomes are best in young animals with healthy retinas and no other significant ocular pathology. Discuss referral options with your primary vet.

What is the difference between nuclear sclerosis and a cataract?

Nuclear sclerosis is a normal, age-related hardening and haziness of the lens that occurs in most horses over the age of ten. It appears as a bilateral bluish-grey haze when viewed in bright light but does not significantly impair vision. A true cataract involves structural protein changes that block light transmission and can affect vision. A vet can distinguish the two on ophthalmic examination. See our horse terminology guide for more equine eye anatomy terminology.