Transcript Eye and Ear - WordPress.com

Structure and function of the eye
https://www.youtube.com/watch?v=IxAD_5X4DCg
Important terms
1. Cornea covers the front of the eye.
2. Iris is the colored part of the eye. It controls the
amount of light that enters the eye by changing the
size of the pupil.
3. Lens - focuses light onto the retina.
4. Optic nerve is the nerve that transmits electrical
impulses from the retina to the brain.
5. Pupil is the opening in the center of the iris. It
changes size as the amount of light changes.
6. Vitreous humour is a thick, transparent liquid
that fills the center of the eye. It is mostly water
and gives the eye its form and shape
7. Aqueous humour - a transparent fluid that fills
the space between the cornea and pupil
8. Retina contains photoreceptors (rods and
cones).
9. Rods – used for night vision. They work well in
dim light.
10. Cones - are able to detect colors such as red,
green, and blue.
11. Fovea centralis - It is the center of the eye's
sharpest vision and the location of most color
perception.
12. Blind Spot - the point where the optic nerve
leaves the eye
How does light travel through the eye?
1.
2.
3.
4.
5.
6.
Cornea
Aqueous humour
Pupil
Lens
Vitreous humour
Retina
https://www.youtube.com/watch?v=RE1MvRmWg7I
How is the amount of light regulated?
- The pupil will dilate (get bigger) if the
amount of light is low
- The pupil will constrict (get smaller) if the
amount of light is too much
How does the eye focus?
The lens will change shape
• When you look at something far away the lens
flattens
• When you look at something close the lens
becomes more rounded.
This adjustment of the lens is called accommodation.
What is the blind spot?
• The blind spot is the point where the optic
nerve leaves the eye and there are NO
photoreceptors.
Disorders of the Eye
1.Cataracts
2.Glaucoma
3.Myopia (Near-sightedness)
4.Hyperopia (Far-sightedness)
5.Astigmatism
Cataracts
• Cataracts are cloudy areas on the lens which
increase over time and can cause blindness.
• Common in older people and may result from
overexposure to sunlight.
• Treatment: Surgery to replace the damaged
lens with an artificial lens.
https://www.youtube.com/watch?v=Go82c4f1emc
Glaucoma
• Glaucoma is caused by too much aqueous
humour building up between the lens and the
cornea.
• The extra fluid causes pressure which destroys
the nerve fibers that control peripheral vision.
• Treatment: Pain medication or Surgery
https://www.youtube.com/watch?v=cF0rj4fM1l0
Myopia or near-sightedness
• When a person has trouble seeing objects far
away.
• It is caused by the eyeball being too long or the
muscles in the eye being too strong
• Treatment: Corrective lenses
Hyperopia or far-sightedness
• A person has difficulty seeing objects which are
close.
• It is caused by the eyeball being too short or the
muscles in the eye being too weak
• Treatment: Corrective lenses
Astigmatism
• An abnormality shaped cornea or lens which
results in an uneven focus.
• The image is focused in front of the retina and
cannot be seen correctly.
• Treatment: Corrective lenses
LASIK
• LASIK is performed for people who are
near-sighted.
• First a knife is used to cut a flap of corneal
tissue, then a laser is used to remove the
tissue underneath the flap and then the
flap is replaced
http://www.youtube.com/watch?v=UezYWOqPQ_Q&safe=active
Surgery
• If the cornea is seriously impaired by disease, a
corneal transplant can be performed.
• A diseased cornea is removed and replaced by
a healthy donor cornea. Recovery is long and
vision improves over 6 to 12 months.
• This is one of the most successful transplant surgeries.
However, it is under utilized because of no donor
corneas?
Do you think it should be mandatory for people
to donate their corneas?
Human Ear
• Three sections of the ear:
1. The outer ear
2. The middle ear
3. The inner ear
Structure of the Human Ear
The Outer Ear
• The outer ear is made up of two
parts:
1. Pinna - catches the sound and sends
it down the auditory canal which
contains tiny hairs and sweat glands
2. Auditory canal - carries the sound to
the eardrum or tympanic membrane
The Middle Ear
Made up of 4 parts:
1. Tympanic membrane (Eardrum)- vibrates when it
receives sound
2. Oval window- a membrane that separates the middle
ear from the inner ear
3. Ossicles - three small bones with vibrate and conduct
sound
a) malleus (hammer)
b) incus (anvil)
c) stapes (stirrup).
4. Eustachian tube - used to equalize air pressure
within the ear.
The Inner Ear
Made up of:
1. Cochlea – involved in hearing
2. Semicircular canals - involved in balance and
equilibrium
How does Hearing Work?
Disorders of the Auditory System
A disorder of the auditory system will
result in some form of deafness.
There are two main types of deafness:
1. Nerve deafness
2. Conduction deafness
Nerve Deafness
• Nerve deafness is caused by damage to the
hair cells in the Cochlea.
• This causes uneven deafness in which you can
hear some frequencies better than others. It
is irreversible.
Conduction deafness
• Conduction deafness is caused by damage to
the outer or middle ear.
• It affects the transmission of sound waves to
the outer ear. People who have this type of
deafness are not totally deaf.
• This type of deafness can be improved by using
a hearing aid.
Hearing Aids
• There are 3 types:
1. Conventional
2. Programmable
3. Digital
How do hearing aids work?
• It has a microphone to receive the sound, an
amplifier to increase the volume of the sound,
and a receiver which transmits the sound to
the inner ear.
What happens when fluid builds-up
behind the eardrum?
• It causes chronic middle ear infections, because of an
improperly angled Eustachian tube which prevents
proper fluid drainage.
• It can be corrected by surgery, in which plastic tubes are
placed in a slit in the eardrum.
• The tube allows for the fluid to drain and this relieves
pressure on the eardrum. As the eardrum heals (which
takes about 6 months to 2 years), the tube is usually pushed out
of the ear.