Like us, horses have the senses of vision, hearing, taste, smell and touch. A horse’s vision is adapted to their needs as both prey animals and grazers. From a scientific or veterinary perspective, vision has been studied more than any of the other senses. Horses have a nearly panoramic field of vision due to their eyes being on each side of their head, estimated to be around 350 degrees with only a small blind spot immediately behind them. This means they can see almost all the way around them without moving their heads. They also have both binocular and monocular vision. The overlapping field of view from both eyes (binocular vision), allows them to perceive depth and/or distances; this is particularly important for navigation and avoiding obstacles and critical in sports involving jumping or where other animals are close by, such as in racing, Polo or carriage driving. Monocular vision allows them to see different things with each eye simultaneously, enhancing their overall visual awareness. The figure below shows a comparison of the horse and human visual field. It’s very clear that the horse can see much more behind itself than we can due to our eyes being placed on the front of our head, but that we have a greater field of binocular vision.
Horses have better night vision than humans. This is due to two things. Firstly, their eyes contain more rod cells, which are specialized for low-light conditions, enabling them to see well in dim light. In addition, they can dilate their pupils to a very large extent allowing more light in. However, they can’t see in complete darkness. Horses have limited colour vision compared with humans. They are essentially red-green colour blind, and whilst they can distinguish between some colours, they don’t see the full range of colours as vividly as we do. This understanding of how horses see colour has been important in changes to the take-off boards and other fixings on racecourses where white, fluorescent yellow and bright blue are clearer for horses to see compared with orange for example. This may also be important when choosing colours to use in fields and around the stable environment.
Horses have also been demonstrated to display visual laterality; that is, in certain circumstances, they can react differently to visual stimuli in one eye compared with the other. For example, it has been shown that horses were more reactive to a fear-eliciting stimulus when presented to the left of the horse. This could be learned behaviour due to the fact that horses are usually handled from the left side as opposed to true innate laterality in vision. However, other studies by other researchers have also suggested that horses have a preference for using the left eye to view objects, people or their environment.
Eye movement in horses can be indicative of reaction to the environment or stress, including pain. Excessive blinking or squinting can be signs of discomfort or pain. Horses may blink more frequently or keep their eyes partially closed to protect them from irritation or injury. This behaviour can indicate conditions such as corneal ulcers, conjunctivitis, or foreign objects in the eye. Excessive tear production or discharge from the eyes can also indicate pain or irritation. Inflammation or injury to the eye can cause increased tear production as the horse’s natural response to protect and lubricate the eye. Rolling or flicking of the eyes can also be a sign of discomfort or pain. Horses may show increased or atypical eye movement when experiencing colic for example. This behaviour is often accompanied by other signs of distress, such as restlessness or pawing. Horses experiencing eye pain or discomfort may be sensitive to light and try to avoid bright sunlight or well-lit areas. They may seek shade or stand with their eyes partially closed to reduce exposure to light, which can exacerbate their discomfort. Any abnormal or exaggerated eye movements, such as rapid flickering or twitching, may indicate neurological issues or pain. These movements may be accompanied by other signs of neurological dysfunction, such as stumbling, incoordination, or changes in behaviour. Swelling, redness, or inflammation around the eye can be signs of underlying pain or injury. These symptoms may accompany conditions such as uveitis (inflammation of the uvea), trauma, or infections. Horses may rub or scratch at their eyes if they are experiencing pain or irritation. However, excessive rubbing can exacerbate the problem and potentially cause further injury to the eye.
Common eye diseases/conditions in horses can include Conjunctivitis, Uveitis or equine recurrent uveitis (ERU) or moon blindness, Corneal Ulcers, Equine recurrent corneal erosion (ERCE), Cataracts, Glaucoma and Equine Recurrent Uveitis (ERU. Several good sources for equine eye conditions are included in the reference list at the end of this article. Eye conditions can progress rapidly and be painful and may lead to loss of sight so it is essential to contact your vet if you suspect your horse has an eye condition.
Key Points
- Horses have a nearly panoramic field of vision due to their eyes being on each side of their head, with only a small blind spot immediately behind them.
- The horse has a smaller field of binocular vision than we do.
- Horses have better night vision than humans.
- Horses can’t see in complete darkness.
- Horses have limited colour vision compared with humans. They are essentially red-green colour blind.
- Good colours to use around horses are white, fluorescent yellow, bright blue, and NOT orange.
- Some studies have shown that horses have a preference for using their left eye for certain tasks.
- A horse’s eyes can communicate pain, stress, confusion or attention, depending on specific circumstances.
- Increased blinking, rolling, squinting, prolonged closing, discharge, swelling, redness, etc, are cause for concern and require consultation with a vet.
References
- Austin NP, Rogers LJ. Asymmetry of flight and escape turning responses in horses. Laterality. 2007 Sep;12(5):464-74. doi: 10.1080/13576500701495307. PMID: 17712716.
- De Boyer Des Roches A, Richard-Yris MA, Henry S, Ezzaouïa M, Hausberger M. Laterality and emotions: visual laterality in the domestic horse (Equus caballus) differs with objects’ emotional value. Physiol Behav. 2008 Jun 9;94(3):487-90. doi: 10.1016/j.physbeh.2008.03.002. Epub 2008 Mar 12. PMID: 18455205.
- Farmer K, Krueger K, Byrne RW. Visual laterality in the domestic horse (Equus caballus) interacting with humans. Anim Cogn. 2010 Mar;13(2):229-38. doi: 10.1007/s10071-009-0260-x. Epub 2009 Jul 17. PMID: 19618222.
- Farrall H, Handscombe M. Equine vision. Equine Vet J. 1999 Sep;31(5):354-5. doi: 10.1111/j.2042-3306.1999.tb03832.x. PMID: 10505948.
- Hall C. The impact of visual perception on equine learning. Behav Processes. 2007 Sep;76(1):29-33; discussion 57-60. doi: 10.1016/j.beproc.2006.09.017. Epub 2007 Mar 4. PMID: 17408877.
- Murphy J, Arkins S. Equine learning behaviour. Behav Processes. 2007 Sep;76(1):1-13. doi: 10.1016/j.beproc.2006.06.009. Epub 2007 Mar 4. PMID: 17400403.
- Paul SC, Stevens M. Horse vision and obstacle visibility in horseracing. Appl Anim Behav Sci. 2020 Jan;222:104882. doi: 10.1016/j.applanim.2019.104882. PMID: 32025069; PMCID: PMC6988441.
- Roberts SM. Equine vision and optics. Vet Clin North Am Equine Pract. 1992 Dec;8(3):451-7. doi: 10.1016/s0749-0739(17)30435-2. PMID: 1458323.
- Rørvang MV, Nielsen BL, McLean AN. Sensory Abilities of Horses and Their Importance for Equitation Science. Front Vet Sci. 2020 Sep 9;7:633. doi: 10.3389/fvets.2020.00633. PMID: 33033724; PMCID: PMC7509108.
Timney B, Macuda T. Vision and hearing in horses. J Am Vet Med Assoc. 2001 May 15;218(10):1567-74. doi: 10.2460/javma.2001.218.1567. PMID: 11393366. - Common Diseases of the Eye (Leahurst Equine Practice, University of Liverpool)
- Common Equine Eye Conditions, Brett Robinson, AAEP
- Eye problems in horses – Oakhill Vets
