AMD Eyes Flashcards
How does light move into our eyes?
Light is reflected by objects we look at and it travels as rays into our eyes.
What happens when we look at distant objects?
When we view distant objects the light enters our eyes in almost parallel lines and so they need a little refraction or bending to focus them as an image on the retina (light-sensitive surface at the back of the eye).
What happens when we view close objects?
Light from close objects spreads as it enters the eye so needs to be refracted more, so the lens relaxes into spherical form
How is light converted into an image?
The eye focuses rays of light onto the retina which sends nerve messages along the optic nerve to the brain where images are interpreted.
What is the eye?
The eye is a tough capsule filled with both watery and jelly like fluids called the humours, that keep the eye in shape and help nourish it.
What is the outside of eye protected by?
by a tough layer called the sclerotic coat (sclera). The sclerotic coat is the white bit we see in our eye.
How does the eye work?
Light entering the eye is refracted by the conjunctiva and cornea and then further refracted by the lens.
When viewing far objects – the lens is stretched into a thinner shape that will refract less.
When reading or viewing close objects – the lens relaxes into is spherical form.
When we age we lose elasticity in our lens which gives us sight issues. This is why we often require reading glasses when we are older.
Define refract?
when a ray of light changes direction when it enters at an angle
What are Rods and Cones?
Light sensitive cells in the retina
What do rods and cones do?
DETECTS LIGHT
These are connected to nerve cells which exit the eye by the optic nerve. The optic nerve leaves the eye where there are no rods and cones and we cannot detect light if it falls on this region – the blind spot
Why do we use rods in darker conditions?
Rods are more sensitive to light and so we use them in darker conditions and to give us early warning (eg: when we see something in the corner of our eye)
Where are rods located?
They are distributed around the sides of the retina and share nerve cells
When do cones work and what do they allow us to do?
Cones work in bright light, allowing us to view colours. They connect to individual nerve cells to provide us with precise vision.
Where are cones located?
They are concentrated at the back of the eye in the macula and in the centre of the retina – the fovea – where there are only cones. This is what we use when we look closely at something.
Whats the pupil do?
Allows light into the eye
