vision Flashcards
draw and label structure of the eye
what is sclera?
tough fibrous protactive layer
role of cornea?
allows light to pass
to focus
role is pupil??
what is it controlled by?
allows light to enter
controlled by iris radius muscle
functoin of lens?
changes shape by ciliary muscles to focus
characteristics of retina
contains photoreceptor cells
what is optic disc?
- blind spot
- no photoreceptors
- where blood vessels enter the eye
what is macula lutea
- area of retina for central vision
- no blood vessels
- fovea is inside
what is the fovea? what are its properties?
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
what is vitrous humour?
provides oxygen and nutrients to the retina
what are the layers of the retina?
function of the pigmented epithelium
trophic function
- provides photoreceptor cells with nutrients
- pigmented
- absorbs light
- prevents light that has not been absorbed from bouncing around eye
- would disturb vision
describe the layer of photoreceptor outer segments
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
describe the outer nuclear layer
contains soma of photoreceptors
describe the plexiform layer
contains horizontal cells
what are horizonral cells role?
- make synaptic connections with photoreceptors and bipolar interneurons
- able to spread vision signals lateral throughout the retina
describe the inner nuclear layer
contains bipolar interneurons
describe the inner plexiform layer
contains amacrine cells
what are the roles of amacrine cells?
signal bipolar interneurons
- can indirectly innervate RGC cells
role of RGC
- receive information from bipolar interneurons
- long axons which project in optic nerve to thalamus
what are retinal ganglion receptive fields?
Area of retina which one retinal ganglion cell can receive information from
how do receptive fields change throughout the eye?
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
why is saccadic eye motion needed?
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
what are saccdic eye motion?
Eyes make quick simultaneous unconscious movements in the same direction
- Allows fovea to move across image field
- Builds up detailed mental map of scene
where are macro-saccadic movements regulated?
Regulated by frontal cortex in front of pre-motor area
what other actions do the eyes make other than saccadic and macrosaccadic movements?
why?
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
describe binocular vision
Retina split into
- temporal hemiretina
- nasal hemiretina
The retina of each eye forms its own complete inverted image of the object
what is the importance of the optic chiams?
leads to binocular vision
how does the optic chiasm lead to binocular vision?
- 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
label
and show the pathway of visual information from the eye to the primary visual cortex
describe ocular dominance
Visual input is separated into discrete columns - into left and right eye columns
- in the primary visual cortex
describe/draw the columnar organisation of the primary visual cortex
and show the importance of this
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
