Physiology of Vision

Question 1

Vision:

Answer 1

insert diagram

Question 2

Optics of Vision

Answer 2

• light travels through the layers of
  globe
• light is refracted
• image formed on the retina by
  phototransduction

Question 3

Phototransduction is

Answer 3

conversion of light/photon energy into neural/electrical potential energy

Question 4

What structures refract light rays in the globe and how?

Answer 4

• cornea = 2/3 = convex = converge
• lens = 1/3 = biconvex = converge

concave lens = diverge light rays
convex lays = converge light rays

Question 5

Refractive power of a material:

Answer 5

• higher the power, more
  convergent/divergent effect on
  rays
• Dioptres D

Question 6

What is the focal length?

Answer 6

• distance from parallel light rays
• entering material t othe point of
  convergence of light rays which is
  normally on the retina
• different dimensions of eye would
  cause refractive error, hence not
  projecting onto the retina

Question 7

Which of the following has the largest refractive power?

Answer 7

last lens

steeper angle

Question 8

Which of the globe structures can change to change refraction of light?

Answer 8

Lens

Question 9

How is the lens controlled?

What lens shown below? Effect?

Answer 9

• ciliary bodies
• cillary muscle contracts -> zonular
  fibers have less tension ->
  spherical lens = more focusing
  power, near focus = PARASYMP
  = closer to eye structures
• ciliary muscle relaxes -> zonular
  fibers are more tense -> flatter
  lens, less focusing power, far focus
  = SYMP = long distance vision

Pilocarpine is a muscarinic receptor agonist
Atropine is a muscarinic receptor antagonist
Muscarinic receptors PARASYMPATHETIC activity

Question 10

Hypermetropia/Hyperopia:

Answer 10

• long sightedness
• eyeball too short or too weak
  refraction
• blurred near vision, good long
  vision

Question 11

Myopia:

Answer 11

• short sightedness
• eyeball too long or too strong
  refraction
• blurred far vision, clear near vision

Question 12

Astigmatism:

Answer 12

imperfect curvature of cornea or lens

blurred near and far vision

Question 13

Presbyopia:

Answer 13

loss of accomodation of eye so loss of near vision

loss in shape of lens changing for near vision; (parasymp)

Question 14

Optics of Vision:

Answer 14

insert diagram

Question 15

Iris Function:

Answer 15

• controls the volume of rays
  entering the posterior segment of
  the globe
• sphincter pupillae -> constricts
  pupil, decreases light in response
  to bright light = parasymp
• dilator pupillae -> dilates pupil,
  increases light in response to dim
  light or fight/flight responses =
  sympathetic

Question 16

Which layer of the eye contains the retina?

The optic part of the retina has how many layers?

What is/are the layer/s called?

Answer 16

• internal neural layer
• non-visual and optic
• optic further divided into external
  pigmented layer and neural
  internal layer
• external = absorbs excess light
  and prevents reflections of light
• internal = neurologically
  functional layer, photosensitive

Question 17

How many cell types in the neural internal layer of the retina?

Answer 17

3 neural cell types

1) photoreceptors: rods and cones
2) bipolar neurons
3) ganglion cells

Question 18

Function of rod cells:

Answer 18

receptive to dim light
light sensitive

Question 19

Function of cone cells:

Answer 19

• receptive to bright light
• colour sensitive receptors

Question 20

What pigment in rods?

Answer 20

rhodopsin (light sensitivity)

Question 21

What pigments in cones?

Answer 21

photopsin (colour sensitivity)

Question 22

What are the two transverse cell types of the neural internal layer of the retina?

Answer 22

• horizontal cells: lateral inhibition
  of bipolar cells
• amacrine cells: contrast
  enhancement and movement
  detection

Question 23

What cell types are involved in colour vision?

Answer 23

• cones = photoreceptors
• L cones/photopsin I: Red
• M cones/photopsin II: Green
• S cones/photopsin III: Blue

Question 24

Red-Green Colour Blindness:

Answer 24

X chromosome linked
hence more common in male
only one mutated copy needed for expression

Question 25

Blue Colour Blindness:

Answer 25

chromosome 7

Question 26

Visual Fields:

Answer 26

image in the environment/external correct orientation

Question 27

Retinal Field:

Answer 27

image in inversion of the visual field image on the retina light travels in straight lines

Question 28

Visual and Retinal Fields:

Answer 28

insert slide

Question 29

Visual Pathway: Components:

Answer 29

optic nerve optic chiasm optic tract lateral genticulate nucleus of thalamus or superior colliculus optic radiation primary visual cortex

Question 30

Ipsilateral Eye Blindness:

Answer 30

- damage to the optic nerve - loss of sight in one eye

Question 31

Bitemporal hemianopia:

Answer 31

- loss of vision on temporal field of both eyes - damage to the optic chiasm

Question 32

Homonymous hemianopia:

Answer 32

- loss of vision on eg the left visual field of both eyes hence one temporal field and one nasal field - damage to the optic radiation fibers

Question 33

Each primary visual cortex will have visual information from both eyes. Draw pathways.

Answer 33

- nasal visual field seen on retinal temporal field - optic nerve - fibers pass through genticulate nucleus on ipsilateral side to the primary visual cortex nasal visual field = ipsilateral primary visual cortex temporal visual field = contralateral primary visual cortex - temporal visual field seen on retinal nasal field - optic fiber - crossed over at optic chiasm - passes through lateral genticulate nucleus - to contralateral primary visual cortex

Question 34

Defects at each number causes?

Answer 34

Question 35

Pituitary gland tumour may result in what visual defect?

Answer 35

- grows upward - squashes optic chiasm - temporal fibers cross and are hence lost - bitemporal hemianopia

Question 36

What might cause homonymous hemianopia?

Answer 36

disturbance top optic radiations on one side stroke, tumour, inflammation, injury

Question 37

Scotoma:

Answer 37

- blind spot - spot loss of vision, unilateral, bilateral, temporary or permanent

Question 38

Visual Agnosia:

Answer 38

inability to recognise visually present objects despite normal visual fields, acuity and colour vision once visual info has gone to primar visual cortex, can project via the temporal ventral route or the parietal dorsal route *ventral route = recognition of object dorsal route = visually guided movements

Question 39

Prosopagnosia:

Answer 39

inability to recognise familiar faces once visual info has gone to primar visual cortex, can project via the temporal ventral route or the parietal dorsal route *ventral route = recognition of object dorsal route = visually guided movements