Somatosensory L4: Vision Flashcards
Why is the eye so important?
Able to see things
_____ is the first and fastest system that senses input
Vision
What does the human eye look like in the internal sagittal view?
What are 3 main structures of the eye?
- Sclera
- Choroid
- Retina
What is the sclera?
Tough outer layer of connective tissue
Keeps it in shape Protector
What does sclera form?
Form visible white part of the eye
What is the cornea?
Anterior, transparent portion of the sclera
What is the purpose of the cornea?
Light rays pass through it before entering interior of eye.
What is the choroid?
middle layer underneath sclera, contains blood vessels that nourish the retina
What are the 2 layers of the choroid layer?
- Ciliary body – controls lens shape
- Iris – controls amount of light entering eye;
What is the ciliary body?
controls lens shape
Near and distant object
What is the iris?
controls amount of light entering eye
By changing shape Iris closes = bright room Iris opens = dim room
Why is it important that the shape/size of the iris changes depending on light?
Eg. what happens when iris is large and is in a bright room = too much light = damage retina
What is the pupil?
Opening through which light enters the eye
What is the purpose of the pupil?
Size adjusted by iris muscles.
What is the retina?
Innermost layer under choroid
What are the 5 cells of the nervous tissue layer of the retina?
- Rods and cones
- Horizontal cells
- Bipolar cells
- Amacrine cells
- Ganglion cells
What is the function of rods and cones?
light detection
What is the function of Horizontal cells; Bipolar cells; Amacrine cells; Ganglion cells?
Signal processing
What are 3 characteristics of pigmented layer?
- Stray light absorption
- Waste product removal
- Nutrients/oxygen delivery from the choroid.
Where are cones and rods situated?
back of the eye
Travel through all there other cells first before reaching
Why are cones and rods at the end?
Need to activate rods and cones without damaging them
Why is it important to have a part of the eye that is important for light absorption?
Light comes in and activates rods and cones and then dissipates into energy
What is the electromagnetic spectrum?
We can detect light from 400-700nm= visible light spectrum
Different wavelength means _____ energy
different
The longer wavelength means ____(more/less) energy.
less
The shorter wavelength means ____(more/less) energy.
more
What are 4 factors influencing lights?
- Absorption: transformation of light energy into heat energy in a medium
- Reflection: when light encounters a medium with different optical density, part or all of its is reflected
- Eg. pigmented layer prevents reflection from occurring
- Refraction: change in propagation direction when passing through media with different optical properties. e.g. air and water
- Ambient noise: light signals can only be detected if they are larger than the background noise. Camouflage: it is hard to see a white rabbit in a snowfield.
- Eg. unless the rabbit moves around or opens its eyes
What is absorption, which is a factor influencing light?
transformation of light energy into heat energy in a medium
What is reflection, which is a factor influencing light?
when light encounters a medium with different optical density, part or all of its is reflected
- Eg. pigmented layer prevents reflection from occurring
What is refraction, which is a factor influencing light?
change in propagation direction when passing through media with different optical properties.
- e.g. air and water
What is ambient noise, which is a factor influencing light?
light signals can only be detected if they are larger than the background noise. Camouflage: it is hard to see a white rabbit in a snowfield
What is refraction?
- Convex surfaces converge light rays.
- Concave surfaces diverge light rays.
Convex surfaces _____ (converge/diverge) light rays.
converge
This is our eyes working
- Lens shaped in convex shape = focus on a focal point
Why is the focal point important?
- Will be sitting on the retina
- Without focal point = blurry
Concave surfaces _____ (converge/diverge) light rays. What does this mean in terms of vision?
diverge
Very difficult to see = no focal point
What are 3 characteristics of refraction in the eye?
- The cornea and lens are the primary refractive structures that bend incoming light rays
- In land animals, the cornea contributes most to the total refractive ability of the eye
- The strength of the lens can be adjusted to accommodate for differences in near and far vision (ACCOMODATION).
What is accommodation?
The strength of the lens can be adjusted to accommodate for differences in near and far vision
Ability to adjust strength of lens by changing its shape
Why is accomodation important in vision?
- Eg. near object = Light rays coming in = light rays are close together = change shape of lens = change focal point
- Eg. distant object = light rays coming in = light rays far away = change shape of lens = change focal point
_____(thicker/thinner) lens means that they can see an object that is distant, far away
Thinner
_____(thicker/thinner) lens means that they can see an object that is near/close
Thicker
In accommodation, how is the shape regulated?
by the ciliary muscle
What is presbyopia?
Age-related reduction in accommodation ability
Muscles and lens are not as flexible (ageing changes)
Age-related reduction in accommodation ability results in ________.
presbyopia
What is myopia?
nearsightedness
- Can’t see far away
What is hyperpia?
farsightedness
- Can’t see close
What is the treatment for myopia and hyperpia?
Need to use extra lens to help with inbuilt lens in eye
What is the accommodation mechanism for seeing something fat away? What are the 4 steps?
- Sympathetic stimulation
- Relaxed ciliary muscles
- Taut suspensory ligaments
- Flattened, weak lens
What is the accommodation mechanism for seeing something fat away? What are the 4 steps?
- Parasympathetic stimulation
- Contracted ciliary muscles
- Slacked suspensory ligaments
- Rounded, strong lens
What does the non- accommodation and accommodation mechanism of vision?
What is myopic (nearsighted) eye?
What is hyperopic (nearsighted) eye?
What are the 3 main layers of excitable cells in the neural portion of retina?
- Photoreceptor layer (outmost) contains RODS and CONES
- Absorption of light and starts circuit/activation
- Middle layer contains BIPOLAR CELLS
- Inner layer contains GANGLION CELLS.
What are 4 steps of the neural retina?
- Rods and cone absorb light
- Bipolar cells connect photoreceptor cells with ganglion cells
- Signal processing starts in the retina
- Axons of ganglion cells join to form optic nerve.
How does the other cells (not rods and cones) provide support and energy?
What is the optic disc?
point on the retina where the optic nerve leaves
What is the blind spot?
The region of the optic disc
No image can be detected in this area because it has no rods or cones.
Why is it called “blind spot”?
Part of retina that cannot detect light
Where the optic nerve exits the eye = no rods and cones in this area
What is the highest point of vision?
Macula lutea
Why do we not see the blind spot?
See with 2 eyes = overlapping = brain fills in missing spot
Can’t see it but it is there
What are the 2 structures of the neural retina?
- Fovea
- Macula lutea
What are 3 characteristics of fovea?
- Small depression in center of the retina
- Has only cones, no bipolar or ganglion cells
- Point of most distinct vision (highest resolution).
Where is the fovea?
Small depression in center of the retina
What type of cells does the fovea have?
Has only cones, no bipolar or ganglion cells
The _____ is the Point of most distinct vision (highest resolution).
Fovea
What are 3 characteristics of macula lutea?
- Area immediately surrounding fovea
- Has cones, bipolar and ganglion cells
- Fairly high acuity.
Where is the macula lutea?
Area immediately surrounding fovea
What type of cells does the macula lutea have?
Has cones, bipolar and ganglion cells
Why do we have the highest point of vision in the middle of the retina?
- When move head = eyes follow
- Look straight ahead = full focus (other bits blurry)
- Evolution = where we normally look
What are 4 characteristics of macular degeneration?
Group of degenerative diseases of the retina:
- Progressive, painless loss of foveal vision
- Fovea = doesn’t have any cells, highest acuity of vision = lose center point of retina
- No cure
- Pigment epithelium function loss – waste products build up, blood vessels grow into retina or pigment epithelium cells die
- Can be genetic = onset at ~30yrs old
What are the 2 types of vision?
- See in the day (light)
- See at night
What are the properties of rod and cone vision with photoreceptors?
What are the 3 parts/structures of rods and cones?
- Outer segment, contains visual pigments that detect light;
- Innersegment, contains metabolic structures
- Synaptic terminals, releases neurotransmitter depending on dark or light exposure detected by the outer segment
What is the outer segment of the photoreceptor structure?
contains visual pigments that detect light
What is the inner segment of the photoreceptor structure?
contains metabolic structures
What is the synaptic terminals of the photoreceptor structure?
releases neurotransmitter depending on dark or light exposure detected by the outer segment
What are spectral sensitivities?
In humans, there are three cone types with peak activation for short (blue), medium (green) and long (red) wavelength light and one rod type with peak activation in blue/green.
Whatever wavelength is outside of this = cannot be detected
What are spectral sensitivities in terms of colour vision?
What are the 4 characteristics for the floor plan of retina?
- There are around 20 times as many rods as cones (120X106 vs 6X106)
- Rods are 1000 times more sensitive to light
- Sensitivity comes at the cost of resolution (acuity)
- The fovea (1.5 deg wide) consists almost exclusively of cones.
How does the image of object project onto the retina?
- Upside down
- Back to front
Brain learns from ____ to interpret images
birth
What is the visual field?
the field of the view that can be seen without moving the head
What are 4 characteristics of visual processing?
- Each optic nerve carries information from both visual fields
- Information is then separated at the optic chiasm;
- The fibres living the chiasm are the optic tract
- each optic tract carries information from one visual field to the opposite visual cortex.
Each optic nerve carries information from ____ (single/both) visual fields
both
Information is then separated at the optic _____
chiasm
The fibres living the chiasm are the optic _____
tract
Each optic tract carries information from one visual field to the opposite ______
visual cortex.
What does the visual pathway look like?
Right side (right eye or left eye) = will go to opposite hemisphere (visual cortex)
What are 2 characteristics of the occipital lobe?
Area V1 is the starting point. Beyond it, there are many more visual areas within the occipital lobe.
Some areas have well established roles and specialties, but the roles of many others are still poorly understood
What are the 2 streams which appear specialised for different tasks?
- Ventral pathway
- Dorsal pathway
What is the ventral pathway important for?
colour processing
“WHAT”
What is the dorsal pathway important for?
Motion and disparity
“WHERE/HOW”
What are Neuropsychology of the Dorsal Stream parietal lobe damage?
- Dorsal Simultanagnosia
- Hemi-Spatial Neglect
What is Dorsal Simultanagnosia?
patients with this disorder find it difficult to perceive multiple objects simultaneously. They often become fixated on a single object within a scene and appear unaware of other objects. This often leads to misperceiving the context of a scene.
What is Hemi-Spatial Neglect?
in neglect, patients often fail to perceive an entire side of an object. Perception of the seen side can be quite normal. Recall of memories made before a stroke are also affected. Both types of deficit suggest that the dorsal stream is important in allocating visual attention. Input going in but perception is gone
What is Ventral Simultanagnosia?
in contrast to dorsal simultanagnosia, all objects are seen, but only one is recognised at a time. It is the recognition process which appears impaired in the ventral form. Can see what it is but can’t recognise/say what it is
What is Associative Agnosia?
typically associated with an inability to recognise or name an object, word or person. In the figure, an optic patient copies the figures successfully but is unable to name or otherwise recognise the objects. In prosopagnosia the deficit appears to be limited to faces
What is sensation without perception; Visual Prosopagnosia?
- Patient who has tumour/trauma
- Can recognise mum (based on smell, voice, clothes)
- Take picture
- Can’t recognise picture of mum
