In a continuation of our function of the eye series we will next go over the function of the iris. The iris known which is mostly for giving eye color has a specific task when it comes to our vision. The iris is a flat and ring-shaped membrane behind the cornea that has an adjustable circular opening in the center ( our pupil). What is known as your eye color actually refers to the color of your iris. Iris color can be blue, green, brown or less common colors, such as grey, hazel (a combination of light brown, green and gold), violet and pink. Despite a common belief, actual change in color of the iris rarely happens. While the color of an eye may appear to change, this is typically due to lighting changes or perception based off nearby colors.
The muscles of the iris
The iris has two sheets of smooth muscle, the “sphincter” muscle is about 1mm wide and circles the pupil. It works to constrict the pupil, while the appropriately named “dilator” muscle is responsible for enlarging the pupil. Your pupil constricts when large amounts of light enter your eye, such as when you move from indoors to outdoors, while it will dilate and allow more light to enter the eye, for instance, when you turn off a light, or go indoors. Changing your focus from distance to near objects, or taking certain drugs, can also cause the pupils to constrict or dilate. Emotions can also cause your pupils to dilate. For example, if you are in a “fight or flight” situation, when the rush of adrenaline starts it will open the pupils to allow it to better assess the situation. For the same reason, the pupils also dilates if you are attracted to someone, the more light that enters the eye, the easier it is to observe the person. Emotion can constrict your pupils as well for example, if you are shown a picture that is frightening or unpleasant, your pupil will automatically constrict in order to let less light into the eye. There is a study devoted to pupil size as an indicator of emotion, known as pupillometrics.
The structure of the iris
In general terms, the iris sits between the cornea and the lens of the eye. The actual iris is flat and acts as a divider that separates the front of the eye (the anterior chamber) from the back of the eye (the posterior chamber).
Your iris is your fingerprint
The colour, structure, pattern and texture of your iris are as unique as your fingerprint. In alternative medicine, iridology is based on the theory that the characteristics of your iris can indicate any health issues elsewhere in your body. Iris recognition (as opposed to retina scanning) is being used more, around the world, as a method of identification, Mexico being the first country to use iris scanning on ID cards (in 2011)
The iris – a summary
The iris is a complex and very essential, hard-working component of the eye – far more than just a pretty colour, even though that is what most of us pay attention to. Together with the pupil, it plays an essential role in vision and an increasingly important role in today’s identification technology.
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