Vision And Audition

Question 0

How does the eye distinguish between the 2 black lines ?

Answer 0

The black lines must fall onto 2 different cones cells to ensure 2 different inputs are received by the brain

Question 1

What is visual acuity testing ?

Answer 1

Testing to determine the maximum distance at which someone can distinguish between 2 lines
This determines the width of a cone cell on the retina
= distance between the lines * length between the cornea and retina/ the distance from the lines to the cornea

Question 2

What were the limitations of the visual acuity test ?

Answer 2

People can start guessing the number of black lines

Person must have 20*20 vision

Question 3

What is the blind spot ?

Answer 3

Point on the optic disk where the ganglion cells exit as the optic nerve and there are few blood vessels entering or exiting the eye

Question 4

How was the size of the blind spot calculated ?

Answer 4

Horizontal distance
= distance between the lines * length between the cornea and retina/ distance from lines to cornea - 1.2mm
Vertical distance
= distance between the lines * length between the cornea and retina/ distance from lines to cornea - 1.9mm
Distance between the centre of the blind spot and the fovea
= distance between the lines * length between the cornea and the retina/ distance from lines to cornea - 4.7mm

Question 5

What does the visual field determine ?

Answer 5

Determines the limitations of what you can see when your eye fixates on an object

Question 6

Why are black/white visual fields different to coloured visual fields ?

Answer 6

Different due to different distributions of rods and cones

Question 7

How can visual fields vary ?

Answer 7

Vary from person to person bases upon their facial structures
Vary depending on whether you are looking at temporal and nasal part of the retina

Question 8

Is the black/white visual field larger than the coloured visual field and if so why ?

Answer 8

Yes
Because the cones which detect colour are concentrated in the fovea which is in the centre of the retina whereas rods are more widely distributed throughout the periphery of the retina

Question 9

What is the difference between the visual field on the temporal side compared to the nasal side ?

Answer 9

Temporal side is more elongated

Question 10

What P type ganglion cells responds to?

Answer 10

Synapse with cones so theses differentiate between different colours

Question 11

What do M type ganglion cells respond to ?

Answer 11

Respond best to fast moving stimuli because they have transient responses

Question 12

Which out of these options has the greatest firing rate and which has the least firing rate ?

• red in centre only
• red in centre and surround
• red in centre and green in surround

Answer 12

Red in the centre only has the highest firing rate because there are no inhibitory inputs
Red in the centre and green in the surround has the lowest firing rate because red and green light express colour opponency so the presence of green light in the surround causes GABA to be released from horizontal cells reducing the output from the on centre bipolar cells onto the ganglion cell

Question 13

What is the ishihara test used for ?

Answer 13

To test colour blindness

Question 14

What are is protonopia?

Answer 14

Lack of red pigment so only blue and green light are received

Question 15

What is deuteranopia ?

Answer 15

Lack of green pigment therefore you can only see red and blue light

Question 16

What is anomalous trichromacy?

Answer 16

All 3 pigments are present but they may have slightly different absorbance characteristics so it affects the requirements for colour matching

Question 17

What is conductive deafness ?

Answer 17

Caused by a disease in the middle ear which interferes with the transmission of sound to the cochlea
- subject is deaf to ordinary air conduction but shows no deafness to bone conduction

Question 18

What is sensorineural deafness ?

Answer 18

Caused by injury or degeneration of the nerve elements on the cochlea or auditory nerve
- subject is deaf to both air and bone conduction

Question 19

What is mixed hearing loss ?

Answer 19

Mixture of both sensorineural and conductive deafness

Question 20

What is air conduction ?

Answer 20

Involves pressure waves moving ossicle bone which moves the fluid in the cochlear causing the basilar membrane to move which in turn causes hair cells to bend transduction the mechanical input into a neural input

Question 21

What is bone conduction ?

Answer 21

Involves placing a vibrating object into the mastoid process which has a direct connection to the cochlear causing fluid movement

Question 22

What is the bone-air gap ?

Answer 22

This is the difference between the threshold frequencies of the 2 conduction mechanisms
- it is caused by abnormalities in the outer or middle ear conduction mechanisms

Question 23

What is rinne’s test ?

Answer 23

1- striking a tuning fork and then holding it to a subjects ear until they no longer hear it. Then immediately placing it the base of the fork onto the mastoid process Person with normal hearing shouldn’t hear anything when the fork is placed on the mastoid process
2- then you repeat this process with the ear blocked - this is mimicking conductive hearing loss so when the tubing forking is placed onto the mastoid process you re-hear the sound
Blocking the ear blocks air conduction so you require a higher frequency sound to hear anything via air conduction but bone conduction has not increased which is why you re hear the sound

Question 24

When is the rinne’s test not useful ?

Answer 24

Not useful in patients with sensorineural hearing loss because both air and bone conduction have been affected equally so if the subject can’t hear it by air conduction then they definitely won’t be able to hear it by bone conduction
If the damage is to the nerve and the Middle ear is in tact then the air conduction would be greater than the bone conduction so they definitely won’t be able to re hear the sound

Question 25

What is webers test ?

Answer 25

Strike a tuning fork and the place the base on the midline of the forehead
- in a normal subject they should hear the sound equally in both ears
- then you block off one ear to mimicking conductive hearing loss and you should hear the sound more loudly int he blocked off ear because the sound is transmitted directly to the cochlear via bone conduction
This is not useful in subjects with bilateral sensorineural hearing loss because both the air and bone conduction thresholds have increased

Question 26

What are the normal threshold for hearing and what are they for a patient with bilateral symmetrical sensorineural hearing loss ?

Answer 26

Normal patient - 30dB

Bilateral sensorineural hearing loss - 40-60dB

Question 27

What is an audiometer ?

Answer 27

It tests receptors across a frequency range

Higher frequency sounds are heard at lower thresholds

Question 28

What is the range for human hearing?

Answer 28

20Hz to 20KHz

Hear higher frequency sounds more loudly and the younger you are the louder higher frequency sounds are heard

Question 29

What is the threshold ?

Answer 29

It is the lowest intensity which can be detected at a particular frequency

Question 30

What are the optimum levels of hearing ?

Answer 30

Between 1-4kHz because this is the normal level for people speaking

Question 31

What are causes of conductive hearing loss ?

Answer 31

Physical damage or blockage of the outer and/or middle ear
Infection/fluid in the middle ear
Otosclerosis- proliferation of bone growth/deposition around the ossicles
Ruptured eardrum causing damage to tympanic membrane

Question 32

What causes sensorineural hearing loss ?

Answer 32

Damage to the inner ear - congenital or infection
Loss/damage of hair cells caused by toxins such as furosemide
BRAINSTEM/neural damage affecting pathway
acoustic neuroma- benign tumour of auditory nerve
menieres disease
meningitis

Question 33

What does peripheral damage normally present itself as compared to Central damage ?

Answer 33

Peripheral is normally monaural whereas central is normally binaural

Question 34

What is presbycusis ?

Answer 34

Is the degeneration of hearing with age - usually gradual and affects both ears equally

Question 35

what is the relationship between sound localisation and time delay ?

Answer 35

direct relationship

Question 36

how does decreasing the amplitude/time difference towards the threshold value affect the ability to lateralise clicks?

Answer 36

it decreases ability to lateralise clicks

Question 37

what is the expected values for interaural time delay ?

Answer 37

100-150 microseconds