T2 L10 Physiology of vision

Question 1

How is focus varied?

Answer 1

Changing shape & power of the lens

Question 2

What does the ray bending?

Answer 2

Cornea does 2/3

Lens does other 1/3 & allows focus to vary (accommodation)

Question 3

What is hypermetropia?

Answer 3

Long sightedness

Eyeball is too short or lens system too weak

Question 4

How is hypermetropia corrected?

Answer 4

Converging lens

Question 5

What is myopia?

Answer 5

Short sightedness

Eyeball is too long or lens system too strong

Question 6

How is myopia corrected?

Answer 6

Add diverging lens

Question 7

What is the refractive power of a lens measured in?

Answer 7

Dioptres
Reciprocal of focal length in metres
2D spectacle has focal length of 0.5m

Question 8

What is the consequence of vertebrate retina evolving back to front?

Answer 8

Ganglion cells & blood vessels are in light path to photoreceptors except in fovea

Question 9

What are the 3 direct processing layers?

Answer 9

Receptors
Bipolar cells
Ganglion cells

Question 10

What are the 2 transverse processing layers?

Answer 10

Horizontal cells

Amacrine cells

Question 11

What happens when a proton hits rhodopsin molecule?

Answer 11

Retinal flips from 11 cis to all trans

Leads to biochemical events resulting from the electrical change (hyper polarisation) in the cell membrane

Question 12

What do ganglion cells respond strongly & weakly to?

Answer 12

Weakly to changes in overall light intensity

Strongly to local contrast i.e. light on a dark background or dark on a light background

Question 13

What is the basic response pattern?

Answer 13

Either on centre or off centre
On cells are stimulated by stimulus in centre & inhibited by stimulus in surrounding
Off cells are inhibited by stimulus in centre & stimulated by stimulus in surrounding

Question 14

What is the sensitivity of red cones?

Answer 14

560nm

Question 15

What is the sensitivity of green cones?

Answer 15

530nm

Question 16

What is the sensitivity of blue cones?

Answer 16

420nm

Question 17

What is the sensitivity of rods?

Answer 17

500nm

Question 18

What is the most frequent type of cone?

Answer 18

Red cone then green cone then blue cone

Question 19

What is the spacing between cones?

Answer 19

2.5 micrometers which corresponds to angle of 0.5 minutes of arc

Question 20

What is colour blindness?

Answer 20

Loss or modification of one of the 3 pigments

Question 21

What genes are on the X chromosome?

Answer 21

Genes for red & green pigment

Question 22

What chromosome is the gene for blue pigment?

Answer 22

Chromosome 7

Question 23

What is central achromatopsia?

Answer 23

Rarer kind of colour blindness

Caused by damage to cortical colour processing areas (V4)

Question 24

Where do optic tracts relay?

Answer 24

In lateral geniculate nucleus of thalamus

A part goes to superior colliculus in midbrain

Question 25

Where does the output of the lateral geniculate nucleus go to?

Answer 25

Striate cortex in occipital lobe (V1)

Question 26

Describe columnar organisation in primary visual cortex

Answer 26

Outer dominance column Smaller orientational columns Colour blobs

Question 27

Describe smaller orientational columns

Answer 27

Orientation of optimal stimuli various systemically across surface

Question 28

Describe colour blobs

Answer 28

Colour information kept separate from orientation | Passed on to other regions e.g. V4

Question 29

What are some causes of partial visual loss?

Answer 29

Left eye blindness Homonymous hemianopia Bitemporal hemianopia Scotoma

Question 30

What are the causes of scotoma?

Answer 30

Retinal damage Lesions in visual cortex Pressure from tumours restricting optic nerve, chasm, optic tract or optic radiation

Question 31

Where does the dorsal stream go and what is it for?

Answer 31

From occipital to parietal cortex Location Motion Action

Question 32

Where does ventral stream go and what is it for?

Answer 32

From occipital to temporal cortex Object & face identity Conscious perception

Question 33

What is visual agnosia?

Answer 33

Person can see but can't recognise or interpret visual information due to disorder in parietal lobes

Question 34

What is visual ataxia?

Answer 34

Person can't describe but can't act

Question 35

What is prosopagnosia?

Answer 35

Inability to recognise familial faces | Associated with damage to specific parts of temporal lobe such as fusiform gyrus on underside of lobe

Question 36

What causes blindsight?

Answer 36

Destruction of striate cortex leading to blindness in part o visual field corresponding to damaged area Individuals not aware of stimuli within blind field but if forced to guess they can perform some discrimination tasks & point accurately to locations of stimuli (blindsight phenomena)

Question 37

What is the vestibulo-occular reflex?

Answer 37

Stabilises gaze by countering movement of head

Question 38

What is optokinetic reflex?

Answer 38

Stabilises image of moving object on retina

Question 39

What is pupillary reflex?

Answer 39

If one eyes is illuminated, both will contract as both pretectal & Edinger Westphal nuclei receive signals from both eyes