17. Retinal Function and Visual Perception

Question 1

What range of electromagnetic wave length is visible to the eye?

Answer 1

400-750 nm

Question 2

What does length of an electromagnetic wave correspond to?

Answer 2

Colour

Question 3

What does amplitude of an electromagnetic wave correspond to?

Answer 3

Brightness

Question 4

What effect does a closer light source have on the focal distance?

Answer 4

Longer focal distance

Question 5

What is accommodation?

Answer 5

Lens alters focal length

Question 6

What are the functions of the pupil?

Answer 6

Control light entering eye

Depth of focus

Question 7

How does the pupil control depth of focus?

Answer 7

Constriction cuts out peripheral light

Question 8

What is the effect of sympathetics on the pupil?

Answer 8

Contract radial muscle of iris

Cause dilation

Question 9

What is the effect of parasympathetics on the pupil?

Answer 9

Contract circular muscle of iris

Cause constriction

Question 10

What is used to test for visual acuity?

Answer 10

Snellen chart

Question 11

What is visual acuity?

Answer 11

Ability to distinguish between 2 nearby points

Question 12

What does each part of 20/20 stand for?

Answer 12

First 20 is distance in feet from Snellen chart

Second is size of the smallest letter read

Question 13

What are the 3 cell types in the retina?

Answer 13

Photoreceptors
Bipolar
Ganglion

Question 14

What do rods detect?

Answer 14

Light intensity

Question 15

Why is visual acuity low in rods?

Answer 15

Many rods converge to the same ganglion

Question 16

What do cones detect?

Answer 16

Colour

Question 17

What is the equation for photon energy?

Answer 17

hv (planck constant x frequency)

hc/ λ (planck constant x speed of light/ wavelength)

Question 18

Which cells are non-image forming photoreceptors?

Answer 18

Retinal Ganglion Cells

Question 19

What do Retinal Ganglion cells control?

Answer 19

Circadian rhythm

Question 20

What light-sensitive pigement is used by retinal ganglion cells?

Answer 20

Melanopsin

Question 21

What is the name for loss of photoreceptor cells?

Answer 21

Macular degeneration

Question 22

What is found in the outer segment of cones?

Answer 22

Discs: specialised receptor region

Question 23

What is found in the inner segment of cones?

Answer 23

Mitochondria and other organelles

Question 24

What is phototransduction?

Answer 24

Converting light to an electrical signal

Question 25

What pigment is used in rods?

Answer 25

Rhodopsin

Question 26

What is rhodopsin composed of?

Answer 26

Retinal and opsin

Question 27

What neurotransmitter is released by rods?

Answer 27

Glutamate

Question 28

What is meant by the dark current?

Answer 28

Na+ enters causing depolarisation | K+ leaves causing repolarisation

Question 29

What happens once light hits rhodopsin?

Answer 29

11-cis retinal converted to 11-trans retinal

Question 30

What does 11-trans retinal activate?

Answer 30

Transducin

Question 31

What does transducin activate?

Answer 31

Phosphodiesterase

Question 32

What is the function of phosphodiesterase?

Answer 32

Cleave cGMP to GMP | Low cGMP closes Na+ channels: hyperpolarisation

Question 33

What are the 3 types of cones?

Answer 33

Blue (short) Green (medium) Red (long)

Question 34

What are the percentage population of each type of cone?

Answer 34

Short: 16% Medium: 10& Long: 74%

Question 35

What is colour blindness?

Answer 35

``` Inherited absence of one or more class of colour pigment L and M cones are x-linked ```

Question 36

What is it called when someone lacks red cones?

Answer 36

Protanope

Question 37

What is it called when someone lacks green cones?

Answer 37

Deuteranope

Question 38

What is it called when someone lacks blue cones?

Answer 38

Tritanope

Question 39

How do photoreceptors adapt to the dark?

Answer 39

Light is insufficient to activate cones | Wait for regeneration of rod rhodopsin (20-30 mins)

Question 40

What is night vision called?

Answer 40

Scotopic vision

Question 41

How do photoreceptors adapt to strong light?

Answer 41

Pigment in rods bleaches | Brain switches to cone-only info processing

Question 42

Which fibres of the optic nerve decussate?

Answer 42

Nasal | Temporal don't

Question 43

Where in the eyes is the left visual field taken in from?

Answer 43

Right side of each eye

Question 44

Where is visually detected movement processed?

Answer 44

Parietal lobe

Question 45

Where is perception of shape and colour processed?

Answer 45

Temporal lobe