How the Eye Works
Light enters the eye through the cornea, which refracts the widely diverging rays of light and bends them through the pupil. The iris limits how much light enters the eye by expanding or contracting the pupil, for example, in dim light, the pupil expands to allow more light in and in bright light, the pupil contracts to allow less light in to the eye. The light then passes through the lens, which refracts the light even more, causing it to converge and cross and therefore, focuses an inverted image onto the retina. The lens can change shape depending on the distance of the object from the eye and therefore, “fine-tunes” the focus. When the light reaches the retina, the rods and cones (photoreceptor cells) convert the image into an electrical signal, which is sent through the optic nerve to the visual cortex of the brain. The brain analyses the information and interprets the signals as light. The brain then reverses the image and, if necessary, fills in the blind spot, leaving the image of what we see through our eyes in our brain.
How the eye protects itself
As well as internal parts, the eye has a couple of external features, which it uses to help to protect itself from harm. One of these is the eyelid, which protects the front part of the eye. The eyelid opens and shuts several times a minute which helps to keep the eye clean and moist. The eyelids have good reflex control, which also helps to prevent the eye from damage. For example, they shut automatically when an object comes too close to the eye or when you move from dim light into bright light. Eyelashes are also important and are joined to the eyelids. They help to keep the eyes clean and free from dirt.
Another method of protection for the eye is through tears. These are secreted from the lacrimal gland, which is above the outer corner of each eye. The tears help to keep the eye moist and to wash away dirt, germs and any other foreign particles for example, dust.