Briefly explain how we see things...
- light hits an object and is reflected in all directions
- when the reflected light ray hits the fovea in the retina, the light sensitive cells of the fovea produce nerve impulses that travel to the brain via the optics nerve
- when the nerve impulses reach the brain an image is created which is what we see
What is refraction and why is it important with regards to seeing things with our eyes?
Refraction is the bending of light. All gift rays entering the eye require refraction so that the light can be directed to the fovea.
List the components of the human eye..
Why does the lens in our eye have the ability to become wider and narrower in relation to the object being viewed? What is this known as?
This is known as accommodation. It allows allows the required amount of light to enter the eye and hit the fovea.
When we look at objects up close, why does it sometimes take us a while to focus?
When light is refracted from close objects it spreads out all over the retina, where it needs to be refracted inwards so it can be focused of on the fovea.
The nerve impulses that arrive at the brain realise the image is not clear.
The brain responds by sending messages to the ciliary muscles.
The ciliary muscles contract, causing the suspensory ligaments to contract and become loose.
This makes the lens thicker and rounder for more refraction of light.
The light is now refracted to hit the fovea of the retina and the image is clear.
What happens when we view objects from a distance?
The light from distant objects is parallel so there is very little refraction.
The brain sends electrical messages to the ciliary muscles causing them to relax.
This causes the suspensory ligaments to tighten and pull the lens to make it narrower.
Describe the lens..
This is a clear transparent structure which changes its shape so that light can be focused on the retina.
Describe the ciliary muscles..
These contract and relax to adjust the thickness of the lens.
Describe the suspensory ligaments
These loosen and become tighter to also adjust the thickness of the lens.
Describe the iris.
This becomes wider and narrower and these movements are used to control the amount of light entering the eye. The movement of the iris is dependent on light intensity.
What is the choroid?
This is the middle layer of the eye which contains blood vessels.
What is the sclera?
This is the outer layer of the eye. It is tough and provides protection.
What is the retina?
The inner layer of the eye. It is light sensitive and contains the fovea which is extremely light sensitive.
What is the fovea?
A very light sensitive area found in the retina of the eye which contains rods and cones.
What is the blind spot?
This is the point where the optic nerve meets the eye. There are no light sensitive cells here.