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As we go deeper into the eye we meet Iris.  The iris is the colored circle surrounding the pupil. It changes the size of the pupil and allows different amounts of light to enter the eye.  One muscle within the iris constricts the pupil in bright light (full sunlight), and another iris muscle dilates (enlarges) the pupil in dim lighting and in the dark.

When people ask you what color your eyes are, they mean what is the color of your iris. The majority of the outer surface of everyone’s eye is white (sclera).  Iris color depends on the amount of melanin pigment.  The less melanin pigment, the lighter the color of the eyes.  Eye color is controlled by family genes.


The pupil is the round, black circle in the center of the iris and is actually a hole through which light passes to the retina.  The size of the opening is controlled by the muscles of the iris, which rapidly constrict the pupil when exposed to bright light and expand (dilate) the pupil in dim light.  Other factors, like drug & alcohol use, concussions & brain injuries, & medications & illnesses can also cause the pupil to dilate or constrict.

Behind the pupil is the lens, a clear, curved structure that focuses light rays that enter through the pupil, making an image on the retina.  It is flexible & elastic allowing you to focus on objects and people that are either nearby or at a distance. The lens provides 25-35% of your eye’s focusing power.  Ciliary muscles are attached to the lens and contract or release to change the lens shape and curvature.  If the lens causes the focus to occur behind the retina, farsightedness occurs. If the lens causes the focus to occur in front of the retina, nearsightedness occurs. Wearing glasses or contact lenses correct these vision problems.

Pupil Iris Lens


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