1. Structure and function of the eye

4. 3. Lens - focuses light onto the retina.
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. 5. Pupil is the opening in the center of the iris
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

6. 8. Retina contains photoreceptors (rods and cones). 9
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.

7. 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

9. How does light travel through the eye?
Cornea
Aqueous humour
Pupil
Lens
Vitreous humour
Retina

12. 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

13. 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.

16. What is the blind spot?
The blind spot is the point where the optic nerve leaves the eye and there are NO photoreceptors.

17. Disorders of the Eye Cataracts Glaucoma Myopia (Near-sightedness)
Hyperopia (Far-sightedness)
Astigmatism

18. 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.

19. 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

20. 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

22. 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

24. 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

26. 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

28. 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?

29. Do you think it should be mandatory for people to donate their corneas?

30. Human Ear Three sections of the ear: The outer ear The middle ear
The inner ear

31. Structure of the Human Ear

32. The outer ear is made up of two parts:
Pinna - catches the sound and sends it down the auditory canal which contains tiny hairs and sweat glands
Auditory canal - carries the sound to the eardrum or tympanic membrane

33. 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
malleus (hammer)
incus (anvil)
stapes (stirrup).

34. 4. Eustachian tube - used to equalize air pressure within the ear.

35. The Inner Ear Made up of: Cochlea – involved in hearing
Semicircular canals - involved in balance and equilibrium

37. How does Hearing Work?

38. 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:
Nerve deafness
Conduction deafness

39. 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.

40. 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.

41. Hearing Aids
There are 3 types:
Conventional
Programmable
Digital

42. 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.

43. 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.