The sclera (white of the eye) is made up of elastin and collagen. The fibrous tunic consists of the sclera and cornea and protects the eye.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. The tapetum lucidum reflects light back onto the retina, allowing for greater absorption in dark conditions. 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 choroid has a great deal of pigment, and is almost entirely made of blood vessels. The vascular tunic (or uvea) is made up of the choroid, the ciliary body, and the iris.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. 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. 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. 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. The nervous tunic (or retina) is made up of cells which are extensions of the brain, coming off the optic nerve.The wall of the eye is made up of three layers: the internal or nervous tunic, the vascular tunic, and the fibrous tunic. However, research has found the horse does not have a ramped retina, as was once thought. The eyeball of the horse is not perfectly spherical, but rather is flattened anterior to posterior. The equine eye includes the eyeball and the surrounding muscles and structures, termed the adnexa. Both the strengths and weaknesses of the horse's visual abilities should be taken into consideration when training the animal, as an understanding of the horse's eye can help to discover why the animal behaves the way it does in various situations. Its visual abilities are directly related to the animal's behavior for example, it is active during both day and night, and it is a prey animal. If you are a person with polycoria, it is necessary to visit your eye doctor regularly for eye checkups to monitor any changes with your vision.The equine eye is one of the largest of any land mammal. The good news is that you may not be required to undergo any treatment if your polycoria does not cause visual impairment and does not interfere with daily activities. Unfortunately, with the extremely rare cases of true polycoria, there is not enough data to determine the success rate of this surgery. This surgery involves cutting through the tissue of the iris to remove the “bridge” that has formed in between the two pupils to improve vision. Pupilloplasty is one of the few treatment options for polycoria. Though, since true polycoria is extremely rare, it can be challenging to determine the best course of treatments for it aside from surgery. However, for those who experience difficulties with their vision, surgery can be an option. Mild cases of polycoria do not require treatment especially if vision remains unaffected. abnormal eye development or pupil margins.However, some conditions have been linked to this condition, such as: The specific underlying cause of polycoria is not yet discovered. a bridge of iris tissue in between the pupils.the oblong shape of the additional pupils.Other accompanying signs and symptoms may include: The obvious sign of polycoria is the presence of two pupils in one eye. This can cause less light to enter the iris, which can cause dim vision and other problems with focusing. In polycoria, the additional pupils are usually smaller than normal and are separated individually in a different segment of the iris. These additional pupils are only holes that are caused by a defect in the iris and do not affect vision. However, they do not possess their own sphincter muscles. This creates the appearance of having more than one pupil in the eye. This condition can affect vision though it is extremely rare.įalse, or pseudopolycoria. Each pupil has its own normally functioning sphincter muscle which allows it to constrict and dilate. This involves two or more separate pupils sharing one eye. It commonly starts during childhood but is often diagnosed later in life. Polycoria affects the pupils and can occur in both or just one eye.
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