Equine Vision – Points to consider when training
Horses are a crepuscular prey species, they are well adapted to visualise their surroundings in lower light levels; they are more active dusk and dawn (or would be if they were wild). They can only visualise colours on the dichromatic spectrum (so your blues and yellows) unlike us humans who can see a trichromatic spectrum of colours!
Okay - so I am going to attempt another user-friendly lesson here! The mechanoreceptors one was a hit; and I received such wonderful comments on how people understood what I was trying to get across – so thank you for the feedback!
I will say here before we begin… that equine vision is a huge subject, this is going to be a whistle stop tour.
Rightio, light travels into the eye and lands on the back layer called the retina. Within the retina there are these things called rods and cones.
Rods sense light in black and white.
Cones sense light in colour (so dichromatic for the horse – they only have blue and yellow cones – but can see green as blue and yellow=green!)
Unlike horses; humans’ cones are clustered centrally, however horses have a significantly lower quantity of cones and a significantly higher proportion of rods.
Horses as I said are crepuscular – they are adapted to lower-light conditions. Rods do not require as much light to enter the eye to be stimulated.
If a horse is to survive their predators in lower light levels, they need eyes that can perceive their surroundings in these conditions. Though in fairness, they have their adaptions for greater light intensity…
So how the hell can they see the fence you’re trying to jump on a sunny day?
Well… horses are pretty cool.
Firstly, their eyes are ginormous and their pupil dilates 6 x more than a humans can!
Secondly, take a look at your horses pupil next time you see them… there is a thing called the corpora nigrans it acts like a visor.
Thirdly, they have what is called a tapetum lucidum (sounds like a wizards spell doesn’t it?) this sits at the back of the retina and deflects light back into the eye.
Fourthly, their eyes are placed at the side of their head – they have both monocular and binocular vision, they can switch between the two which is really cool and gives them this “panoramic view” of the world, but they do have a blind spot in front of their nose and behind their tail.
Does your horse tilt their head slightly on the approach to a fence? He is judging the distance. Watch my videos of Nemo jumping – he makes it very obvious! Whilst we need to approach as straight as we can, expect that your horse may need to tilt his head to get a better view of the fence.
Fun fact: If you’re jumping a red fence… your horse can’t actually see it as clearly as say…a blue one. Horses also find it easier to jump fences with multiple block colours as opposed to a single colour – it helps them differentiate the fence from their environment.
Another challenge for the horse visually, is adapting quickly to changes in light intensity.
Unlike humans, it takes a longer amount of time for this to happen in horses. Say for example, your horse has been in a dark trailer and they are unloaded into a sunny environment. Your horse will not be able to adjust quickly resulting in them being unable to see their surroundings properly.
Yikes! No wonder they don’t always like the trailer! Imagine how scary it would be that every time you left the trailer, you were blinded?
Next fun fact; horses can be near or far sighted just like humans – some horses need to be right on the fence before they see it; whereas some horses may see it further away; but as they get closer their focus may become stunted. If your horse is constantly taking strides out or knocking poles down, it could be worth investigating with your veterinarian.
Other points to consider…
Working in constant collection impairs their field of vision, more so if they are behind the vertical.
Horses can be over stimulated visually – it is innate for them to be on the lookout for predators, so their spookiness is all about survival!
Do you do target training? Or desensitise them to different objects?
Then you need to know that horses see with the most clarity at eye level, this is because their retina is saturated with what are known as ganglion cells.
What are ganglion cells?
In short, they take visual information and make sense of it – so say a ball was being chucked at you; it would be your ganglion cells that process the shape, colour and speed in which it was being thrown. And would therefore trigger further bodily/brain responses, which would then hopefully mean you would duck in time. (That’s a really, really simple explanation they are incredibly complex!)
There has been a study conducted by K.E Evans, P.D Greevy (2006) that there is a positive correlation between nasal length and the saturation of ganglion cells found in the retina of different breeds of horses...I haven't got access to this paper - but if anyone has happened to read it I'd love to know the outcome of their findings!
I fear I have digressed a little, so without making this post any longer I am going to rein myself in (excuse the pun), as I could easily write a book on this subject as it is so vast! But my take home message would be just to consider what the world actually looks like to your horse? Be mindful of it, and understand that some “acting out” behaviour could be a result of how they visually perceive the world.
I encourage you to read some of the references, particularly the 4th one if you’re looking for a user-friendly article to understand the equine eye in more detail (you can find the article online).
References: 1.) K.E Evans, P.D McGreevy ‘The Distribution of Ganglion Cells in the Equine Retina and its Relationship to Skill Morphology’ Faculty of Veterinary Science, University of Sydney 2006 2.) Equisearch, Horse Vision and Eyesight, www.equisearch.com , 2017 3.) J.L Jones, How your horse’s vision differs from yours, Equus Magazine, 2016 4.) L Sandmeyer, Understanding Equine Vision and Eye Disease, Horse Journal, 2015