vision

Question 1

draw and label structure of the eye

Answer 1

Question 2

what is sclera?

Answer 2

tough fibrous protactive layer

Question 3

role of cornea?

Answer 3

allows light to pass

to focus

Question 4

role is pupil??

what is it controlled by?

Answer 4

allows light to enter

controlled by iris radius muscle

Question 5

functoin of lens?

Answer 5

changes shape by ciliary muscles to focus

Question 6

characteristics of retina

Answer 6

contains photoreceptor cells

Question 7

what is optic disc?

Answer 7

• blind spot
  
  • no photoreceptors
• where blood vessels enter the eye

Question 8

what is macula lutea

Answer 8

• area of retina for central vision
• no blood vessels
• fovea is inside

Question 9

what is the fovea? what are its properties?

Answer 9

inside the macula lutea

• thin
• gives the highest definition images
• Has the smallest retinal ganglion cell receptive field
  
  • Single ganglion cell receives input from only one photoreceptor
  • (cone) -> colour and fine acuity
  • No amacrine or horizontal cells - no lateral signalling

= very high visual acuity

Question 10

what is vitrous humour?

Answer 10

provides oxygen and nutrients to the retina

Question 11

what are the layers of the retina?

Answer 11

Question 12

function of the pigmented epithelium

Answer 12

trophic function

• provides photoreceptor cells with nutrients
• pigmented
  
  • absorbs light
  • prevents light that has not been absorbed from bouncing around eye
    
    • would disturb vision

Question 13

describe the layer of photoreceptor outer segments

Answer 13

photo receptor – 2 types

rods

• sensitive to low intensity light
• only b and w

cones

• need higher intensity of light to be activated
• provide colour vision and higher resolution
• 3 different cones – respond to different wavelengths

Question 14

describe the outer nuclear layer

Answer 14

contains soma of photoreceptors

Question 15

describe the plexiform layer

Answer 15

contains horizontal cells

Question 16

what are horizonral cells role?

Answer 16

• make synaptic connections with photoreceptors and bipolar interneurons
• able to spread vision signals lateral throughout the retina

Question 17

describe the inner nuclear layer

Answer 17

contains bipolar interneurons

Question 18

describe the inner plexiform layer

Answer 18

contains amacrine cells

Question 19

what are the roles of amacrine cells?

Answer 19

signal bipolar interneurons

• can indirectly innervate RGC cells

Question 20

role of RGC

Answer 20

• receive information from bipolar interneurons
• long axons which project in optic nerve to thalamus

Question 21

what are retinal ganglion receptive fields?

Answer 21

Area of retina which one retinal ganglion cell can receive information from

Question 22

how do receptive fields change throughout the eye?

Answer 22

smallest at fovea

become larger towards the periphery

• has more horizontal and amacrine cells
• at periphery = better light sensitivity but lower visual acuity and ability to resolve detail

Question 23

why is saccadic eye motion needed?

Answer 23

Periphery of retina has lots of rods & large receptive field size

• = good at detecting low light and movement
• But periphery provides little visual detail - large receptive field size

Fovea - fine detail images

• But only collects information from a few degrees of visual field

Question 24

what are saccdic eye motion?

Answer 24

Eyes make quick simultaneous unconscious movements in the same direction

• Allows fovea to move across image field
• Builds up detailed mental map of scene

Question 25

where are macro-saccadic movements regulated?

Answer 25

Regulated by frontal cortex in front of pre-motor area

Question 26

what other actions do the eyes make other than saccadic and macrosaccadic movements?

why?

Answer 26

Eyes also make continuous smaller oscillations to refresh retinal image

• Retinal image quickly fades when eyes are still - as rods and cones only respond to changes in luminance

Question 27

describe binocular vision

Answer 27

Retina split into

• temporal hemiretina
• nasal hemiretina

The retina of each eye forms its own complete inverted image of the object

Question 28

what is the importance of the optic chiams?

Answer 28

leads to binocular vision

Question 29

how does the optic chiasm lead to binocular vision?

Answer 29

• Temporal portion project to LGN of thalamus on same side
• RGC in nasal cross over to other side
• Partial images from both retinas go to the LGN
• That visual information sent to primary visual cortex
• Partial images from both retinas to thalamus
  
  • Integration of both
  • Whole central visual

Question 30

label

and show the pathway of visual information from the eye to the primary visual cortex

Answer 30

Question 31

describe ocular dominance

Answer 31

Visual input is separated into discrete columns - into left and right eye columns

• in the primary visual cortex

Question 32

describe/draw the columnar organisation of the primary visual cortex

and show the importance of this

Answer 32

ocular dominance on layer IV - there are columns

input from layer IV to layers II and III

Neurons can receive monocular input

• From only one neuron
• Purple areas
• Colour sensitive
• Not orientation

Can receive binocular

• Orientation
  
  • not colour