Learning Objectives 13: Special Senses

Question 1

What is the difference between ophthalmologists, optometrists, and opticians?

Answer 1

ophthalmologists
MD specializing in diseases of the eye and eye surgery
optometrists
doctors of optometry who examine eyes to check for disease and deficits in vision
opticians
technicians who fit and sell corrective lenses

Question 2

Identify and describe the 10 structures of the eye

Answer 2

Retina
the light-sensitive layer that lines the interior of the eye
Optic nerve
the second cranial nerve in vertebrates, which conveys sensory impulses from the eye to the brain
choroid
the layer of the eyeball between the retina and the sclera. It contains blood vessels and a pigment that absorbs excess light and so prevents blurring of vision
sclera
the white fibrous outer layer of the eyeball
cornea
the transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina
iris
the part of the eye that regulates the amount of light that enters. It forms a coloured muscular diaphragm across the front of the lens; light enters through a central opening, the pupil
lens
the transparent crystalline structure situated behind the pupil of the eye. It helps to refract incoming light and focus it onto the retina
ciliary body
the part of the eye that connects the choroid with the iris. It contain the ciliary muscle, contraction of which alters the curvature of the lens
aqueous humor
the watery fluid that fills the chamber of the eye immediately behind the cornea and in front of the lens.

Question 3

What two structures of the eye function to bend and focus light on the retina? Which of these structures is fixed? Which can change its shape?

Answer 3

the cornea and lens. the cornea is fixed while the lens can change shape

Question 4

What does “accommodation” refer to? How does the shape of the lens change as we focus on an object closer to our eye?

Answer 4

accommodation is the lens changing shape as to focus on objects at varying distances
when we focus on an object closer to our eye the lens becomes thicker, shorter, and fatter

Question 5

Determine if an individual’s vision is poor or good given their acuity fraction

Answer 5

A acuity fraction of 20/20 is normal vision
20/x=you can read at 20 feet away what a normal person can ready at x feet away
so larger than 20 on the bottom is poorer than normal vision

Question 6

What is a focal plane? To have the clearest vision, where do we want the focal plane to be?

Answer 6

A focal plane is where light rays converge in the eye. To have the clearest vision it is best for the focal plane to be located on the retina

Question 7

What is refractive error?

Answer 7

refractive error is an irregularly shaped eye or lens causing light to be bent incorrectly and the focal plane not to be aligned on the retina

Question 8

What is hyperopia? What causes it? What does an individual with hyperopia have difficulty seeing?

Answer 8

hyperopia is farsightedness. It is caused by a shorter than normal eye causing the focal plane to be located behind the retina. One with this condition has difficulty seeing objects near them

Question 9

What is myopia? What causes it? What does an individual with myopia have difficulty seeing?

Answer 9

Myopia is nearsightedness. It is caused by a longer than normal eye causing the focal plane to be located in front of the retina. One with this condition will have difficulty seeing objects far from them

Question 10

What is presbyopia? What causes it? What does an individual with presbyopia have difficulty seeing?

Answer 10

presbyopia is farsightedness with age due to the lens hardening over time. an individual with this has difficulty seeing objects near them

Question 11

What is astigmatism? What causes it? How does astigmatism impact an individual’s vision?

Answer 11

Astigmatism is a condition of no point (multiple focal points in the eye). It is caused by an oval shaped cornea, and it causes blurred vision

Question 12

How is refractive error corrected?

Answer 12

refractive error is typically corrected with corrective lenses. Surgery is also an option in some cases

Question 13

What structure of the eye does laser eye surgery alter?

Answer 13

the cornea

Question 14

What is glaucoma? How does it develop? What structures of the eye are ultimately damaged? How will the vision of an individual with glaucoma be impacted? What test does your optometrist perform to test for glaucoma?

Answer 14

glaucoma is increased pressure in the eye caused by a blockage of the drainage canal of aqueous humor. It ultimately damages the optic nerve and blood vessels of the eye. This condition causes an individual to have loss of their peripheral vision.
optometrists use an air puff test to test for glaucoma

Question 15

What are cataracts? What structure of the eye do cataracts impact? How are they treated?

Answer 15

Cataracts are a clouding of the lens due to clumping of proteins that typically happens with age. The lens is the eye structure impacted. They are treated by a surgery called phacoemulsification.

Question 16

What structures are involved with keeping the eyes moist?

Answer 16

The lacrimal glands which produce tears that move across the surface of the eye to the puncta, then those tears travel down the nasolacrimal duct into the nose

Question 17

Identify and describe the 7 structures of the ear. What makes up the outer ear, middle ear, and inner ear?

Answer 17

outer ear
auricle/pinna
the flap of skin and cartilage that projects from the head at the exterior opening of the external auditory meatus of the ear
ear canal/auditory canal
the passage that extends from the external opening of the ear to the eardrum; the external auditory meatus
eardrum/tympanic membrane
separates outer and middle ear
When sound waves reach the ear the tympanum vibrates, transmitting these vibrations to the malleus – one of the auditory ossicles in the middle ear – to which it is attached
middle ear
eustachian/auditory tube
equalizes pressure in ears
ossicles
The auditory ossicles are three small bones (the incus, malleus, and stapes) in the middle ear. They transmit sound from the outer ear to the labyrinth (inner ear)
inner ear
cochlea
transduces vibration into electrical signals
semicircular canal
regulates balance

Question 18

What two cavities does the auditory tube connect?

Answer 18

the middle ear (tympanic cavity) and the nasopharynx

Question 19

Explain in general how the ears transduce sound waves to electrical signals.

Answer 19

the tympanic membrane converts sound waves to vibration
vibrations of the tympanic membrane are transmitted by the ossicles to the fluid within the cochlea
the vibrations of the fluid in the cochlea cause some hair cells in the cochlea to best, these cells transform this vibration into electrical signal sent to the brain via the cochlear nerve

Question 20

What type of cells transform vibrations to electrical signals to be sent to the brain?

Answer 20

hair cells (specialized neural cells)

Question 21

What is presbycusis? What causes it? Can it be treated? How or why not?

Answer 21

presbycusis is hearing loss with old age. It is caused by degeneration of hair cells over time. It cannot be traits because damage to hair cells is irreversible

Question 22

What is NIHL? What causes it?

Answer 22

NIHL is noise induced hearing loss. it is caused by damage to hair cells caused by chronic or acute exposure to sounds outside the safe listening decibel range

Question 23

Less than how many decibels is considered safe for listening to?

Answer 23

<85 Decibels

Question 24

In order to prevent NIHL, as you increase the decibels of noise what do you need to shorten?

Answer 24

duration of exposure

Question 25

For safe listening you should keep the volume of your personal listening device no louder than what percentage of the maximum volume?

Answer 25

60% of the maximum volume

Question 26

What type of headphones are beneficial for helping to prevent NIHL? (as long as you keep them at an appropriate volume level)

Answer 26

noise canceling headphones

Question 27

What is tinnitus? What causes it?

Answer 27

tinnitus is perceived ringing in the ears caused by bent or broken hair cells continuing to send electrical signal to the brain despite there being no sound

Question 28

What is otitis media? What causes it? Who is most susceptible to otitis media? Why? How is otitis media treated?

Answer 28

otitis media is inflammation of the middle ear. It is often caused by an infection of the middle ear. Children are most susceptible due to their short auditory canal (easier for pathogens to reach middle ear), their auditory tubes are more level (more difficult to drain), and their immune systems are still developing.
It can be treated with tympanostomy/myringotomy, in which a pressure equalizing tube is inserted into an surgical incision in the ear drum for a temporary period of time.

Question 29

Draw and label the parts of the ear

Question 30

Draw and label the parts of the eye