Structure and function of the eye https://www.youtube.com/watch?v=IxAD_5X4DCg

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. 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

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.

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? 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 Cataracts Glaucoma Myopia (Near-sightedness) Hyperopia (Far-sightedness) 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 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: The outer ear The middle ear The inner ear

Structure of the Human Ear

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

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).

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

The Inner Ear Made up of: Cochlea – involved in hearing 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: Nerve deafness 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: Conventional Programmable 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.