Horses have captivated the human imagination for centuries.
Their vision of the world is unique, shaped by millions of years of evolution and adapted to their particular way of life.
How does a horse see?
Horses have remarkable panoramic vision, covering nearly 350 degrees around them. This ability comes from the lateral position of their eyes. Their orientation is adapted to their lifestyle and nutrition. As a result, they can quickly detect predators in the wild.
However, this peripheral vision can sometimes lead to gaps in their perception of objects directly in front and behind them.
Anatomically speaking, a horse’s vision consists of the eyes and the organs appendages.
Housed in the orbit, the eye comprises the bulb, also known as the eyeball, and the optic nerve. Optic nerve, which carries visual impulses to the visual pathways and centers of the brain.
Other organs enable the horse to see properly :
– the external muscles of the bulb, surrounded by fascia and adipose tissue, accompanied by vessels and nerves. They are enclosed with the eye in the orbit.
– the eyelids and conjunctiva.
– the lacrimal apparatus.
Horse vision: a world in motion
Horses’ vision is strongly linked to their way of life. They are able to detect distant movements: a skill inherited from their wild ancestors who depended on vigilance to escape predators.
Even today, the horse’s world is a ballet of movements and visual signals. But unlike us humans, horses perceive the world with a more restricted palette of colours.
Horses are sensitive to shades of blue and green, but have difficulty with reds and oranges.
Adapted to life in the open air, their eyes excel at detecting subtle variations of light.
Zooming in on the organs that enable equine vision
The eye bulb : an essential organ for equine vision
In the horse, the eye bulb is not spherical, but clearly flattened in the anteroposterior anterior-posterior direction by about 45mm, while the horizontal diameter is between 50 and to 54mm wider than the vertical diameter (which is 45 to 50mm).
The angle of divergence between the two optical axes is 70 to 90 degrees. The weight of each eyeball weighs close to 60 grams in an adult horse, but can exceed exceptionally over 70 grams.
Note: the eyeball weighs 35 grams in a donkey.
The sclera : the white of the eye
Also known as the sclera, the sclera is composed of tough connective tissue and covers almost the entire eyeball. Its mission is to protect the eyeball. The sclera is very solid, and contains no melanocytes.
The thickness of the sclera is minimal at the equator: between 0.3 and 0.5 mm.
It is considerably thicker at the anterior pericorneal margin: around 1.5 mm.
It reaches its maximum thickness in the posterior pole region at 2 mm.
The cornea : essential to the proper functioning of the horse’s vision
The cornea is an ocular component essential to the functioning of equine vision.
In fact, it is the first structure encountered by light entering the eye.
Its main role is to converge the incident rays of light, which are then directed through the anterior chamber of the eye, towards the crystalline lens, before meeting the retina the retina and initiate the visual cascade.
What does the horse’s cornea look like?
The cornea is a non-vascularized, transparent tissue with a curved geometry. It is similar to a hemispherical dome, and is often compared to a porthole located at the front of the eye, in direct contact with the air. It is also covered by a tear film.
The choroid: the retina’s ally
The choroid is a thin layer of tissue located between the sclera and the retina. It contains numerous blood vessels supplying the oxygen and nutrients to the retina.
It contains many melanocytes, which absorb light to help reduce reflection inside the eye. This mat has a bluish color, sometimes yellow or dark green, reflecting an iridescent metallic sheen.
The ciliary body : variator of the lens
The ciliary body is the anterior portion of the choroid to which the lens is attached lens, via the suspensory ligaments. It lies at the junction between the iris and the choroid.
On its posterior surface are the ciliary processes, which secrete aqueous humor, the gelatinous liquid contained in the front of the eye, between the cornea and the lens.
Its muscular fibers help the eye to focus on near or distant objects by modifying the shape of the lens.
The iris : guarantor of light
The iris is the thin, colored part of the eye. It is composed of muscular tissue.
Located between the cornea and the crystalline lens, the iris modifies the size of the pupil in order to regulate the amount of light entering the eye. It contains melanocytes, cells that produce a pigment called melanin.
The amount of melanin in the iris defines the color of the eye.
The crystalline lens : for the eye’s focus
The crystalline lens is a transparent, disk-shaped structure contained in the inner part of the eye. It lies directly behind the cornea and iris. It adapts its shape to enable the eye to focus on objects near or distant objects.
Light rays pass through the crystalline lens and are focused on the retina to create images of objects at different distances from the body.
Horses’ night vision
Horses are also equipped with impressive night vision. Their eyes capture more light and their pupils can adjust quickly to changes in
brightness. They are trusted companions for those who like to ride in the moonlight…
To sum up, a horse’s vision is much more than just visual perception.
It’s the totality of their senses interacting in complex ways to form a holistic understanding of their environment.
Combined with keen hearing and a keen sense of smell, horses have a complete picture.