Wikijunior:Human Body/Eyes

What is an eye?

The eye is a very perplexing system that allows us to view things. Here you will find a lot about the eye. But remember, this is not a professional page, but rather an outline.

What is the function of the eyes? (Function)

Eyes are the parts of our body that perceive light. They allow us to see the world and to understand how objects relate to each other. We can distinguish far objects from close ones and determine their color and shape. The eye acts like a camera where the eye-lens is a replacement of camera-lens, eye-lid of shutter and retina of photographic film.

What do eyes look like? (Appearance)

A close up of a human eye.

The eye is almost spherical in shape. The eye-ball is about of 2.3cm diameter. We perceive eyes together with eyelids and eyebrows which make up one main characteristic of the face.

What are the parts of the eyes? (Parts)

Eyes are made of several different parts. The white part of the eye is called the sclera.(It is interesting to note that only in Human Species among all other creatures that sclera is visible when the eyes are open). 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 is a coloured diaphragm 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. It is made up of jelly-like crystalline substances and is convex in nature. Between the lens and cornea is a fluid called aqueous humour.Similarly, inside the major part of eye ball is vitreous humour.

The retina is the lining of the inside back of the eye. It is the part of the eye that translates the information from the light into the language of the brain i.e. electric impulses. 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.

Most of the reflection takes place through cornea, aqueous humour and vitreous humour and the lens merely function to focus the image on retina. The lens is held by ciliary muscles which also controls the curvature of lens to accommodate it to see distant and close objects clearly.

How do the eyes interact with other parts of the body? (Interaction with other Body Parts)

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. This vision helps us to judge the distance accurately and provides us a 3D vision of the world. 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? (Connections)

Illustration shows how the muscles and nerves attach to the eye.

The optic nerve connects the eyes with the brain. Several eye muscles (4 rectus and 2 oblique muscles) attach the eyes to the skull and perform eye movements to control our gaze and visual focus and the power of accommodation of our eyes.

How can you keep your eyes healthy? (Health)

You should avoid putting your hands or any other object in the eyes. Wearing safety goggles when doing construction work can protect your eyes from injury. You should not watch television or use a computer for long periods of time. You should keep books at a distance of about 25cm while reading. Avoid looking at bright objects (like the sun) for too long as it can damage your eyes and even make you blind.