The Eye

HOW DO
WE SEE?

Learn more about how light passes through the lens and sends signals through the optical nerve, to your brain.

1. Light reflects off objects and travels in a straight line to your eye.
2. Light passes through the cornea, into the pupil and through the lens.
3. The cornea and lens bend (refract) the light to focus on the retina.
4. Photoreceptors on the retina convert the light into electrical impulses.
5. The electrical impulses pass along the optic nerve to the brain.
6. The brain processes the signals to create an image.

THE ROLE OF
THE EYES

Your eyes play a crucial role in almost everything you do. Here are some of the main functions of the eye.

Seeing- Eyes take in light and convert it into electrical impulses that are sent to the brain, which processes these signals to form the images we see.

Moving- The six ‘extraocular’ muscles control the movement of the eye. Four move the eyeball up, down, left and right; two adjust the eyes to counterbalance head movement.

Blinking- Every time you blink, a salty secretion (basal tears) from your tear gland is swept over the surface of the eye, keeping your eyeballs moist and clean. Muscles in the upper eyelid control the opening and shutting movement.

Crying- Tears – salty fluid containing protein, water, mucus and oil – are released from the lacrimal gland in the upper, outer region of the eye. Reflex tears protect the eye from irritants like smoke, dust and wind. Emotional tears are a response to sadness or joy – there’s a theory that ‘a good cry’ can help the body get rid of toxins and waste products.

Protecting- The eyes are set in sockets in the skull to protect them from injury. Eyelashes and eyelids keep out dust and dirt. Eyebrows are arched in shape to divert sweat away from your eyes.

COMPONENT
PARTS

Below are the component parts of the eye and a brief explanation of their role in allowing you to see the world around you.

Sclera- The ‘white’ of the eye that protects the eyeball and gives it it's firm, regular shape.

Pupil- The black hole at the centre of the eye that allows light through.

Iris- The coloured part of the eye that controls the amount of light passing through the pupil.

Cornea- A transparent dome that protects the iris and pupil. Together with the lens, the cornea bends (refracts) light to focus it onto the back of the eye.

Crystalline lens- A transparent disc that sits behind the iris.

Retina- The back of the eye that contains millions of photoreceptors (sensors that convert light into electric impulses.) These signals are sent along the optic nerve to the brain, where they are processed to create an image.

Macula- A small spot near the middle of the retina that is responsible for central vision.

Vitreous humor - A jelly-like substance that fills the middle of the eye, giving it form and shape.

Optic nerve- The nerve at the back of the eye that carries signals from the retina to the brain.

Conjunctiva- A thin membrane that gives the eye protection and helps keep it moist. It lines the inside of the eyelid and the surface of the eyeball.

Aqueous humour- A clear fluid that lies in the space between the iris and the cornea. This maintains eye pressure and gives the front of the eye its rounded shape.