Undesired behaviours in horses are often attributed to training, tack, rider input or temperament. However, a recent peer-reviewed article highlights an important and sometimes overlooked contributor: ocular disease.
In Ocular Causes for Undesired Behaviors in the Horse, equine ophthalmologist Kelly E. Knickelbein explores how eye pain and visual impairment can directly influence how horses behave, perform and respond to handling and work.
Pain, vision and behaviour are closely linked
Knickelbein’s article explains that many ocular conditions cause significant pain, visual disturbance or both. These changes can manifest as behaviours that owners and professionals may label as “naughty”, unpredictable or resistant, including:
- Head shyness
- Headshaking
- Spooking or shying
- Balking or refusing to go forward
- Rearing
Importantly, some horses are highly stoic. They may show minimal outward signs of eye disease despite experiencing considerable discomfort or reduced vision. In these cases, behavioural changes may be the first, or only, clue that something is wrong.
Recognising signs of ocular pain
Horses experiencing eye pain may show obvious indicators such as blepharospasm (tight blinking), eyelid swelling, ocular discharge or rubbing at the eye. When these signs are present, the author stresses that horses should be rested from work to avoid worsening the condition and to reduce the risk of pain-related behaviours becoming established.
However, the absence of visible signs does not rule out an ocular problem.
Why assessing equine vision is challenging
One of the key points raised in the paper is how difficult it is to assess what a horse can truly see. Owners often ask what “percentage of vision” a horse has retained following eye disease, but current clinical tests cannot provide this level of certainty.
This limitation makes it even more important to consider ocular causes when unexplained behavioural changes arise, particularly if other common causes have been ruled out.
Common ocular conditions linked to behaviour
The article reviews several eye disorders that may influence behaviour, including:
- Corneal ulcers and lacerations, which cause severe pain due to the cornea being one of the most densely innervated tissues in the body
- Uveitis and vitreous degeneration, where inflammation and so-called “floaters” may interfere with vision
- Phthisis bulbi, an end-stage, non-functional and often painful eye that may require surgical removal to restore comfort
- Corpora nigra cysts, which can obstruct the pupil and are associated with spooking and shying
- Cataracts, which may develop with or without uveitis and impair visual clarity
Some of these conditions are treatable, and in certain cases, addressing the ocular issue can lead to meaningful improvements in behaviour.
The importance of a full ophthalmic examination
Knickelbein emphasises that horses showing undesired behaviours without an obvious explanation should undergo a complete ophthalmic examination. This should include pupil dilation to allow full assessment of deeper structures such as the lens, vitreous and fundus.
Where standard examinations are inconclusive but suspicion remains high, advanced diagnostics such as electroretinography or retinoscopy may be warranted.
Handling and treatment matter too
The article also highlights how the treatment process itself can influence behaviour. Poor handling, rushed medication application or inappropriate techniques can quickly create or worsen head shyness, complicating both treatment and future handling.
A calm, patient and consistent approach is essential, particularly as many ocular conditions require intensive or long-term management.
A reminder to look beyond behaviour
This paper reinforces a crucial message for horse owners, trainers, vets and therapists alike: behaviour is often communication. When a horse’s behaviour changes, especially in ways that seem linked to fear, uncertainty or resistance, the eyes should not be overlooked.
Considering ocular health as part of a wider investigation may not only improve performance and safety, but also significantly improve welfare by identifying and relieving pain that might otherwise go unrecognised.
Please read Kelly E. Knickelbein, VMD’s full article – Click Here.
