The Eye Flashcards
(24 cards)
What is the eye?
A sense organ
That contains receptors sensitive to light intensity and colour
What is the cornea?
A transparent lens at the front of the eye
that refracts (bends) light as it enters the eye
(Starts the focusing of the light rays)
What is the iris?
The pigmented part of the eye
which controls how much light enters the eye by changing the size of the pupil
What is the pupil?
The hole in the iris that allows light to enter the eye
What is the lens?
The transparent disc that can change shape to focus light onto the retina at the back of the eye
What is the retina?
It contains light receptor cells
Rods - detect light intensity
Cones - detect colour
What does the optic nerve do?
It is a sensory neurone that carries impulses between the eye and the brain
What is the structure order of how the eye sees light?
6
Cornea Iris Pupil Lens Retina Optic nerve
What is the sclera?
The white tough outer layer which protects the eye
What is the ciliary muscles?
It can change the thickness and curvature of the lens to allow the eye to focus
What is the suspensory ligament?
Fibres that attach the lens to the ciliary muscles
What type of focus in the cornea?
A fixed focus
What is accommodation?
This is where the lens changes shape to focus on near or distant objects
How does accommodation take place?
The lens is surrounded by ciliary muscles which are attached by suspensory ligaments
By contracting/relaxing the ciliary muscles can change the thickness of the lens
When the ciliary muscles contract the suspensory ligament loosens making the lens thicker + refracts light rays more strongly
When the ciliary muscles relax the suspensory ligaments are pulled tight making the lens thinner + only slightly refracts light rays
How does accommodation enable us to do us on distant objects?
Distant objects only need to be focused a relatively small amount
So the ciliary muscles relax the suspensory ligaments are pulled tight making the lens thinner + only slightly refracts light rays
The light rays are focused to a point on the retina
How does accommodation enable us to do us on near objects?
Light from objects need to be focused on a large amount
When the ciliary muscles contract the suspensory ligament loosens making the lens thicker + refracts light rays more strongly
The light rays are focused to a point on the retina
What is long sightedness also called?
Hyperopia
What is long sightedness?
People who can focus on distant objects fine
But cannot focus on nearby objects
What usually causes someone to be long sighted?
2
Their eyeball being too short which causes light to be focused on a point behind the retina
The lens becomes less elastic which stops the lens becoming thick enough to focus on nearby objects (more common in elderly)
How can long sightedness be treated?
By using glasses with convex lenses which partially focus the light before it enters the eye
What is short sightedness also known as?
Myopia
What is short sightedness?
People who can focus on nearby objects fine
But cannot focus on distant objects
What usually causes someone to be short sighted?
2
Their eyeball being too long which causes light to be focused on a point in front of the retina
Can also be caused by the lens being too thick causing the light to be focused in front of the retina
How can short sightedness be treated?
Using glasses with concave lenses to partially unfocus the light before it enters the eye
