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This article was provided by AllAboutVision.com. Follow the links below for more information on eye health and vision correction.
The human eye has been called the most complex organ in our body. It's amazing that something so small can have so many working parts. But when you consider how difficult the task of providing vision really is, perhaps it's no wonder after all.
How the Human Eye Works
The human eye is like a camera. Light comes in through the cornea, a clear cover that is like the glass of a camera's aperture. The amount of light coming in is controlled by the pupil, an opening that opens and closes a little like a camera shutter.
The light focuses on the retina, a series of light-sensitive cells lining the back of the eye. The retina acts like camera film, reacting to the incoming light and sending a record of it via the optic nerve to the brain.
Other parts of the human eye play a supporting role in the main activity of sight:
- Some carry fluids (such as tears and blood) to lubricate or nourish the eye.
- Others are muscles that allow the eye to move.
- Some parts protect the eye from injury (such as the lids and the epithelium of the cornea).
- And some are messengers, sending sensory information to the brain (such as the pain-sensing nerves in the cornea and the optic nerve behind the retina).
How Light Travels Through the Eye
In order to see, we must have light. While we don't fully understand all the different properties of light, we do have an idea of how light travels. A light ray can be deflected, reflected, bent or absorbed, depending on the different substances it encounters.
When light travels through water or a lens, for example, its path is bent or refracted. Certain eye structures have refractive properties similar to water or lenses and can bend light rays into a precise point of focus essential for sharp vision.
Most refraction in the eye occurs when light rays travel through the curved, clear front surface of the eye (cornea). The eye's natural (crystalline) lens also bends light rays. Even the eye's tear film and internal fluids (aqueous humor and vitreous) have refractive abilities.
How the Eye Sees
The process of vision begins when light rays that reflect off objects and travel through the eye's optical system are refracted and focused into a point of sharp focus.
For good vision, this focus point must be on the retina. The retina is the tissue that lines the inside of the back of the eye, where light-sensitive cells (photoreceptors) capture images in much the same way that film in a camera does when exposed to light. These images then are transmitted through the eye's optic nerve to the brain for interpretation. Just as a camera's aperture (called the diaphragm) is used to adjust the amount of light needed to expose film in just the right way, the eye's pupil widens or constricts to control the amount of light that reaches the retina. In dark conditions, the pupil widens. In bright conditions, the pupil constricts.
Articles on our website are courtesy of AllAboutVision.com. Visit their site for more information about eyeglasses, types of contact lenses and various eye conditions.
Article ©2011 Access Media Group LLC. All rights reserved. Reproduction other than for one-time personal use is strictly prohibited.
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