The eye Flashcards
Name the different parts in the structure of the eye
- Cornea
- Pupil
- Iris
- Ciliary muscles
- Suspensory ligaments
- Lens
- Retina
- Rods &Cones
- Optic nerve
What is the function of the cornea
the cornea is curved and transparent, it refracts light and focuses it onto the lens
What does the iris do?
The iris is the coloured part of the eye, it contracts and relaxes to control the volume of light that gets into the eye
What is the funciton of the pupil?
The pupil is a gap which allows light to enter the eye
What is the funtion of the ciliary muscles?
The ciliary muscles contract and relax which tightens or slackens the suspensory ligaments to change the shape of the lens
What is the function of the suspensory ligaments?
The suspensory ligaments connecte the lens to the ciliary muscles. They slacken or tighten when the ciliary muscles contract or relax to change the shape of the lens
What is the funciton of the lens?
The lens refracts light to focus it onto the retina
It can change shape, allowing us to focus on near or far objects
What is the funtion of he retinaa?
The retina detects light
Name the two light receptors on the retina
- Cones
- Rods
What is the funtion of the cones on the retina
they detect the colour of light
What is the function of the optic nerve
The optic nerve is a sensory neurone which sends electrical impulses form the eye to the brain
What is the function of the sclera?
The sclera is the tough white outer layer on the eye which protects the eye form damage
Maintains the shape of the eye
How does the eye accomodate to focus on near objects?
Accomoation in the eye
- The ciliary muscles contract
- This causes the suspensory ligaments to slacken
- This causes the lens to become round and fat, so it can refract light more strongly
How does the eye accomodate to focus on far away objects?
Accomodation in the eye
- The ciliary muscles relax
- This cause the suspensory ligaments to become stretched and tighter
- This causes the lens to become long and thin so it refracts light less strongly
How do the muscles in the eye adapt to bright light
- The light receptors in retina detect dim light levels
- Electrical impulses transmitted across neurone
- Causes the ciliary muscle contracts and gets smaller
- The radial muscles relax so pupil then constricts
This limits the volume of light that can enter the eye to protect the retina as it is very sensetive to light
it is an unconscious process so the brain is NOT invloved
How do the muscles in the eye adapt to dim light?
- Light detectors in retina detect dim light levels
- Electrical impulses travel along neurone
- Causes the ciliary muscles relax and become larger
- The radial muscles contract so the pupil is dilated
This allows a larger volume of light to enter the eye
It’s an unconscious process. So the brain is not involved
What is myopia?
Myopia (shortsightedness)
Is when the lens refracts light too much so the image is brought into focus infront of the retina
What causes myopia to occur
1) The lens is too round and thick. so it refracts light too much
or
2) The lens in too far away from the retina
What type of corrective lens in used to correct myopia
Concave lens
How does the concave lens correct myopia
It refracts light less strongly so the image focuses on the retina
What is hyperopia?
hyperopia (long-sightedness) is when the lens does not refract the light enough so the immage is brought into focus behind the retina
What are the two causes of hyperopia?
1) The lens is too long and thin, so it does not refract light enough
or
2) The eyeballis too short so the lens is too close to the retina
Which type of corrective lens is used to correct hyperopia?
Convex lens
What does a convex lens do?
It refracts light more strongly so that the image is focused onto the retina
Name the new technologies which have been used to correct eye defects
- Hard or soft contact lenses
- Laser eye surgery to change the shape of the cornea
- Replacement lens in the eye
How is laser eye surger used to correct myopia?
A laser is used to vaporise tissue
This changes the shape of the cornea
Slimming down the cornea causes light to be refracted less strongly so the image is focused onto the retina
How is laser eye surgery used to correct hyperopia?
The laser is used to vaporise the tissue
This changes the shape of the cornea
The shape of the cornea is changed to become thicker so that the light is refracted more strongly and the image is focused onto the retina
What are the risks and disadvantages of laser eye surgery?
It can cause infection
The eye may react in a way that makes vision worse
It’s expensive
What do contact lenses do?
Contact lenses sit on the surface of the eye to help it to refract light correctly
What are advantages and disadvantages of contact lenses
Adv:
They are lightweight
soft lenses are comfortable
Convinient for sport
Disadv:
Soft lenses carry a higher risk of infection
Makes eyes dry
Can only be worn for a certain amount of hours
What is lens relacement surgery?
When a faulty lens is surgically removed and replaced with an artificial plastic lens
What are disadvantages of lens replacement
It is extremely risky as it could damage the retina. This means that the patient would lose their eyesight altogether.
Why is the reflex of adapting our eyes to dim/bright light important
The retina and the light detectors (cones and rods) on the retina are extremely sensetive to bright light and can be damaged if they are exposed to light which is too bright.
This reflex is therefore important as it controls the volume of light that enters the eye.
State the name of the process which changes the shape of the lens
Accomodation
