<P> The equine eye includes the eyeball and the surrounding muscles and structures, termed the adnexa . </P> <P> The eyeball of the horse is not perfectly spherical, but rather is flattened anterior to posterior . However, research has found the horse does not have a ramped retina, as was once thought . </P> <P> The wall of the eye is made up of three layers: the internal or nervous tunic, the vascular tunic, and the fibrous tunic . </P> <Ul> <Li> The nervous tunic (or retina) is made up of cells which are extensions of the brain, coming off the optic nerve . These receptors are light - sensitive, and include cones, which are less light - sensitive, but allow the eye to see color and provide visual acuity, and rod cells, which are more light - sensitive, providing night vision, but only seeing light and dark differences . Since only two - thirds of the eye can receive light, the receptor cells do not need to cover the entire interior of the eye, and line only the area from pupil to the optic disk . The part of the retina covered by light - sensitive cells is therefore termed the pars - optica retinae, and the blind part of the eye is termed the pars - ceaca retinae . The optic disk of the eye, however, does not contain any of these light - sensitive cells, as it is where the optic nerve leaves to the brain, so is a blind spot within the eye . </Li> <Li> The vascular tunic (or uvea) is made up of the choroid, the ciliary body, and the iris . The choroid has a great deal of pigment, and is almost entirely made of blood vessels . It forms the tapetum lucidum when it crosses over the fundus of the eye, causing the yellowish - green eye shine when light is directed into the animal's eyes at night . The tapetum lucidum reflects light back onto the retina, allowing for greater absorption in dark conditions . The iris lies between the cornea and the lens, and not only gives the eye its color, (see "eye color," below) but also allows varying amounts of light to pass through its center hole, the pupil . </Li> <Li> The fibrous tunic consists of the sclera and cornea and protects the eye . The sclera (white of the eye) is made up of elastin and collagen . The cornea (clear covering on the front of the eye) is made up of connective tissue and bathed in lacrimal fluid and aqueous humor, which provides it nutrition, as it does not have access to blood vessels . </Li> <Li> The lens of the eye lies posterior to the iris, and is held suspended by the ciliary suspensory ligament and the ciliary muscle, which allows for "accommodation" of the eye: it allows the lens to change shape to focus on different objects . The lens is made up of onion - like layers of tissue . </Li> </Ul>

What does a normal horse eye look like