How Eyes Work Flashcards
What is a far point?
A far point is the most distant point an eye can focus on. For a normal eye this is infinite. The lens is at is thinnest when looking at vet distant objects like the moon.
What is the near point?
The near point for a normal eye is the closest point on which an eye can focus. This is about 25cm for adults with normal vision
What is the pupil
The round hole in the centre of the eye. It can change its simple in response to changes in light levels
How does the eye focus an image that is far away
The ciliary muscles relax making the ring of muscles wide and so the lens is pulled into a thin shape
What is the iris
Coloured ring that controls the size of the pupil and so controls how much light enters the eye
What’s the cornea
Outer transparent layer of the eye that refracts light entering the eye
What’s the retina
Tissue at the back of the eye that contains light receptors.
What’s the lens
Further converges light rays (which have been refracted by the cornea) to focus them on the retina
What happens when light reaches the retina
The image formed is converted into electrical impulses by cells in the retina and neurones carry impulses (along the optic nerve) to the brain which interprets them
How does the eye focus an image that is near
The ciliary muscles contract making the ring of muscles smaller and so the lens relaxes into a fatter shape
