Human+Body+-+Eyes

Human Body/Eye

 * Interactive Lesson:** [|**The eye**]

What do eyes look like?
The eye proper is almost spherical in shape. We perceive eyes together with eyelids and eyebrows which make up one main characteristic of the face.

What are the parts of the eyes?
Eyes are made of several different parts. The white part of the eye is called the **sclera**. This part covers the surface of the eyes except at the very front. At the front of an eye is a **cornea**. This part acts like a shield for the eye. It can still let light pass through because it is transparent. Under the cornea is the **iris** and **pupil**. The pupil is the black circle in the middle. It is actually a hole that lets light pass through into the back of the eye. The iris the coloured part around the pupil. It is a muscle that opens and closes around the pupil to let more or less light through. Behind the pupil is a **lens** that focuses the light that passes through it onto the **retina**. The retina is the lining of the inside back of the eye. It is the part the part of the eye that translates the information from the light into the language of the **brain**. The retina is lined with thousands of tiny **rods** and **cones** which detect the color and amount of light shining onto them. The optical information gathered by the rods and cones is passed via the **optic nerve** at the back of the eye to the brain. A diagram of the parts of the eye.

How do the eyes interact with other parts of the body?
The brain processes the raw data from the eyes to make sense of what you see compared to your knowledge of the world around you. The brain interprets what it receives from the eyes. You do not directly "see". A clear example of this can be seen from experiments where subjects wear glasses that invert the view (turn it upside down). After a while the brain will adjust and turn the scene back up the right way because that agrees with other more reliable information you are receiving. Similarly the brain adjusts changes in color and light levels to better match how the objects should appear. It also combines the two slightly different views from your left and right eyes to work out the distance of objects from you. Your right eye will show a little more of an object's right side and the left eye will show more of an objects' left side. This is called **stereoscopic vision**. The difference between the views from each eye becomes less the further the object is away from you. Our perceptions are not perfect and can lead to misinterpretations of what we see. These are called **optical illusions**. However even though the brain's processing can be inaccurate, at most times we perceive a faithful reconstruction of the real world. Only optical illusions remind us that there is at times a difference between perception and the true state of affairs. Without our eyes and the complex processing of visual information by our brains we would not be able to make sense of writing, art or photos, nor understand as much as we do from limited visual information. 

What organ systems are the eyes connected with?
Illustration shows how the muscles and nerves attach to the eye. The optic nerve connects the eyes with the brain. Several eye muscles attach the eyes to the scull and perform eye movements to control our gaze and visual focus. 

How can you keep your eyes healthy?
You should avoid putting your hands or any other object in the eyes. Wearing safety goggles when doing construction can protect your eyes from injury. You should not watch television or use a computer for long periods of time.