The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and then to the brain. The eye works much the same as a camera. The shutter of a camera can close or open depending upon the amount of light needed to expose the film in the back of the camera.
The eye, like the camera shutter, operates in the same way. The iris and the pupil control how much light to let into the back of the eye. When it is very dark, our pupils are very large, letting in more light. The lens of a camera is able to focus on objects far away and up close with the help of mirrors and other mechanical devices.
The lens of the eye helps us to focus but sometimes needs some additional help in order to focus clearly. Glasses, contact lenses, and artificial lenses all help us to see more clearly. Updated visitor guidelines. Anatomy of the Eye. When it is dark, our pupils dilate or open wider to allow more light in. Doing this maximizes our vision. In bright light, our pupil shrinks to a very small diameter to protect the sensitive photoreceptors in our retina.
This is exactly the role that the pupil plays in the eye. The pupil reacts to external light and changes its size accordingly. That is why when we go into bright sunlight, we involuntarily squint — we almost close our eyes to limit the sudden excess of light entering. Once the pupils have adjusted to the light by becoming smaller, we no longer need to squint. Otherwise, we would be very light sensitive. This protects the sensitive photoreceptors in our retina.
Also, when we look at something at a very close distance such as reading a book, our eyes converge and our pupils shrink. When our pupils shrink, it is similar to looking through a pinhole.
Looking through a small hole reduces peripheral blur and increases the depth of focus. This improves overall visual acuity. Normal pupil size is between 2. The iris , the colored part of our eye, is made up of pigment and contains two sets of smooth muscles that control the size of the pupil: the sphincter muscle and the dilator muscle.
The sphincter muscle is in the shape of a ring at the margin of the pupil. When it contracts, it constricts or decreases the size of the pupil. The dilator muscles are in a radial shape throughout the iris and when it contracts, it dilates or increases the size of the pupil.
Both systems, the parasympathetic and sympathetic systems control the pupil. Our parasympathetic system controls everyday activities such as rest, slowing the heart rate and things like digestion.
It controls the pupil size during normal activities during the day and acts to change the pupil size depending on how much light is present. The sympathetic system is a protective system and gives us the typical "fight or flight" responses. The eye is a complex and delicate mechanism. Knowing the different parts of the eye and how they function will help you recognize vision problems or…. Can eye exercises help improve your vision? Here are techniques you can try.
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Iritis, also known as anterior uveitis, involves the inflammation of the iris, the colored part of your eye. It's important to get medical care if you…. Learn more about how long eye strain can last, what changes you can make to your work station to help, and when to see a doctor. Health Conditions Discover Plan Connect. About Normal Pupil Sizes. Medically reviewed by Ann Marie Griff, O.
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