The Human Eye
Science: KS3, topic 3.3.23
The Human Eye
The human eye is the organ that senses and reacts to light and allows us to visualise what is around us. Different parts of the eye include:
The cornea
- This is the transparent outside layer of the eye. Light is focused into the eye.
The pupil
- Light enters the pupil, which is just a hole.
- The pupil is able to change size depending on how much light there is.
- When it is dark, the pupil will be bigger to let in more light.
- When it is sunny, the pupil will be smaller.
- This is why if someone turns the light on just after you have woken up, it hurts your eyes.
- Your pupils will be large because it was dark just before this happened.
The iris
- The Iris is a muscle that controls the size of the pupil, and so the amount of the light that enters the eye and the amount that can reach the retina.
- The iris can be different colours, with 55% of the world’s population having brown eyes and 10% having blue.
The lens
- The lens is a transparent structure that is able to change shape. It is found behind the Iris.
- The lens will focus light onto the retina.
- Sometimes, the lens will not focus light directly onto the retina.
- If the lens becomes cloudy, this is known as cataracts.
- If the lens doesn’t focus light correctly onto the retina, you may need glasses.
The retina
- The retina is the back of the eye where the light is focused.
- This is made up of rod and cone cells (photoreceptors).
- When light hits the rod and cone cells, they form electrical impulses.
The optic nerve
- The optic nerve is a nerve that connects the eye to the brain. The eye sends signals along this nerve and the brain can then form images.
- Because of the optic nerve’s position, your eye actually has a blind spot.
- When light rays hit the retina, the image formed is actually upside down. It is your brain that turns it around.
Test yourself on The Human Eye
Why do your eyes hurt if someone turns on a bright light straight after you wake up?
Which of these are correct descriptions of parts of the eye?
Which of these are correct descriptions of parts of the eye?
How do the jobs of the cornea and the lens differ?