Physiology of Vision Flashcards
1
Q
Eye and Retina
- Optically, the eye is quite like a camera
- Cornea and lens produce a … image on the …
- … is varied by changing the shape and power of the lens
- The iris acts as a diaphragm, varying its diameter by 4x, and thus retinal intensity by 16x
- Behind the retina is a pigment layer which absorbs … light
A
- Optically, the eye is quite like a camera
- Cornea and lens produce a focused image on the retina
- Focus is varied by changing the shape and power of the lens
- The iris acts as a diaphragm, varying its diameter by 4x, and thus retinal intensity by 16x
- Behind the retina is a pigment layer which absorbs unwanted light
2
Q
Eye and Retina
- Optically, the eye is quite like a camera
- … and … produce a focused image on the retina
- Focus is varied by changing the shape and power of the …
- The … acts as a diaphragm, varying its diameter by 4x, and thus retinal intensity by 16x
- Behind the retina is a pigment layer which absorbs unwanted light
A
- Optically, the eye is quite like a camera
- Cornea and lens produce a focused image on the retina
- Focus is varied by changing the shape and power of the lens
- The iris acts as a diaphragm, varying its diameter by 4x, and thus retinal intensity by 16x
- Behind the retina is a pigment layer which absorbs unwanted light
3
Q
View of the retina through an opthalmoscope
- The main feature here is the optic … - where the optic nerve leaves the eye and blood vessels enter and leave the …
- The … is the small yellow spot on the far right - in outside space it covers a thumb nail at arm’s length (1-2 degrees)
A
- The main feature here is the optic disc - where the optic nerve leaves the eye and blood vessels enter and leave the retina
- The fovea is the small yellow spot on the far right - in outside space it covers a thumb nail at arm’s length (1-2 degrees)
4
Q
- The … does 2/3 of the ray bending
- The … does the other 1/3, but also allows the focus to vary (Accommodation)
A
- The cornea does 2/3 of the ray bending
- The lens does the other 1/3, but also allows the focus to vary (Accommodation)
5
Q
- The cornea does 2/3 of the ray bending
- The lens does the other 1/3, but also allows the focus to vary (…)
A
- The cornea does 2/3 of the ray bending
- The lens does the other 1/3, but also allows the focus to vary (Accommodation)
6
Q
Common focusing problems - refractive errors
- … - long sightedness:
- Eyeball too short or lens system too weak
- … - short sightedness: - more common
- Eyeball too long or lens system too strong
- Correction is usually via spectacle or contact lenses. The refractive power of a lens is measured in diopters (D)
- This is the reciprocal of focal length in metres: a 2D spectacle lens has a focal length of 0.5m.
A
- Hypermetropia - long sightedness:
- Eyeball too short or lens system too weak
- Myopia - short sightedness: - more common
- Eyeball too long or lens system too strong
- Correction is usually via spectacle or contact lenses. The refractive power of a lens is measured in diopters (D)
- This is the reciprocal of focal length in metres: a 2D spectacle lens has a focal length of 0.5m.
7
Q
Common focusing problems - refractive errors
- Hypermetropia - … sightedness:
- Eyeball too short or lens system too weak
- Myopia - … sightedness: - more common
- Eyeball too long or lens system too strong
- Correction is usually via spectacle or contact lenses. The refractive power of a lens is measured in … (D)
- This is the reciprocal of focal length in metres: a 2D spectacle lens has a focal length of 0.5m.
A
- Hypermetropia - long sightedness:
- Eyeball too short or lens system too weak
- Myopia - short sightedness: - more common
- Eyeball too long or lens system too strong
- Correction is usually via spectacle or contact lenses. The refractive power of a lens is measured in diopters (D)
- This is the reciprocal of focal length in metres: a 2D spectacle lens has a focal length of 0.5m.
8
Q
Hypermetropia = …
A
- Hypermetropia - long sightedness:
- Eyeball too short or lens system too weak
9
Q
Myopia = …
A
- Myopia - short sightedness: - more common than hypermetropia (long)
- Eyeball too long or lens system too strong
10
Q
Structure of the retina
- Vertebrate retina evolved back to front: ganglion cells and blood vessels are in the light path to the photoreceptors (except in the ,,,)
- Receptors:
- 120 million rods (dim light)
- 5 billion cones (3 types - bright light and colour)
- Processing layers:
- 3 direct layers (receptors, bipolars and ganglion cells)
- 2 transverse layers (horizontal and amacrine cells): signal processing including lateral inhibition - sharpening up images
- Only 1 million retinal ganglion cells per eye: 125:1 convergence into optic nerve
A
- Vertebrate retina evolved back to front: ganglion cells and blood vessels are in the light path to the photoreceptors (except in the fovea)
- Receptors:
- 120 million rods (dim light)
- 5 billion cones (3 types - bright light and colour)
- Processing layers:
- 3 direct layers (receptors, bipolars and ganglion cells)
- 2 transverse layers (horizontal and amacrine cells): signal processing including lateral inhibition - sharpening up images
- Only 1 million retinal ganglion cells per eye: 125:1 convergence into optic nerve
11
Q
Structure of the retina
- Vertebrate retina evolved back to front: ganglion cells and blood vessels are in the light path to the photoreceptors (except in the fovea)
- Receptors:
- 120 million rods (dim …)
- 5 billion cones (3 types - … light and …)
- Processing layers:
- 3 direct layers (receptors, bipolars and ganglion cells)
- 2 transverse layers (horizontal and amacrine cells): signal processing including lateral inhibition - sharpening up images
- Only 1 million retinal ganglion cells per eye: 125:1 convergence into optic nerve
A
- Vertebrate retina evolved back to front: ganglion cells and blood vessels are in the light path to the photoreceptors (except in the fovea)
- Receptors:
- 120 million rods (dim light)
- 5 billion cones (3 types - bright light and colour)
- Processing layers:
- 3 direct layers (receptors, bipolars and ganglion cells)
- 2 transverse layers (horizontal and amacrine cells): signal processing including lateral inhibition - sharpening up images
- Only 1 million retinal ganglion cells per eye: 125:1 convergence into optic nerve
12
Q
Rhodospin and it’s chromosome - retinal
- Rhodospin is the … pigment in the rods
- When hit by a photon the retinal in the rhodospin molecule flips from 11-cis to all-trans (chemical change of molecule)
- This sets off a series of biochemical events which results in closure of cGMP- gated nonselective cation channels that are open in the dark, leading to hyperpolarization of the photoreceptor and a reduction in the release of the neurotransmitter …
A
- Rhodospin is the photosensitive pigment in the rods
- When hit by a photon the retinal in the rhodospin molecule flips from 11-cis to all-trans (chemical change of molecule)
- This sets off a series of biochemical events which results in closure of cGMP- gated nonselective cation channels that are open in the dark, leading to hyperpolarization of the photoreceptor and a reduction in the release of the neurotransmitter glutamate.
13
Q
The ganglion cell response - the output of the retina
- Unlike the receptors, ganglion cells respond very weakly to changes in overall light intensity. Instead, they respond to local …: … on a … background or … on … background.
- Ganglion cell responses are of many kinds, but the basic pattern is either on-centre (left) or off-centre (right). This is due to lateral …. Fields tend to be circular
- Ganglion cells send action potentials down the optic nerve: receptors and bipolars have only graded electrical potentials.
- Right - bright light in centre with dark surround - signal shut off - followed by revamped AP - stimulus removed
- Bright stimulus - no effect
- No light in centre - bright light around - increase in AP in photoreceptor
A
- Unlike the receptors, ganglion cells respond very weakly to changes in overall light intensity. Instead, they respond to local contrast: light on a dark background or dark on alight background.
- Ganglion cell responses are of many kinds, but the basic pattern is either on-centre (left) or off-centre (right). This is due to lateral inhibition. Fields tend to be circular
- Ganglion cells send action potentials down the optic nerve: receptors and bipolars have only graded electrical potentials.
- Right - bright light in centre with dark surround - signal shut off - followed by revamped AP - stimulus removed
- Bright stimulus - no effect
- No light in centre - bright light around - increase in AP in photoreceptor
14
Q
Rhodospin is the photosensitive pigment in the …
A
Rhodospin is the photosensitive pigment in the rods
15
Q
Rhodospin is the photosensitive pigment in the …
A
Rhodospin is the photosensitive pigment in the rods
16
Q
Unlike the receptors, ganglion cells respond very weakly to changes in overall light …. Instead, they respond to local …: light on a dark background or dark on a light background.
A
Unlike the receptors, ganglion cells respond very weakly to changes in overall light intensity. Instead, they respond to local contrast: light on a dark background or dark on a light background.
17
Q
Colour vision - trichromacy
- Red cone - 560nm
- Green cones - 530 nm
- Blue cones - 420 nm
- Rods - 500nm
- Rods not on diagram - Peak sensitivity of about 500nm
A
- Red cone - 560nm
- Green cones - 530 nm
- Blue cones - 420 nm
- Rods - 500nm
- Rods not on diagram - Peak sensitivity of about 500nm
18
Q
Living cone mosaic near the edge of the fovea
- There are typically more red cones than green cones, and far fewer … cones than either of the other two (Getting pictures like this involves impressive optical engineering. The colours are false)
- The spacing of the cones is about 2 micrometers, and corresponds to an angle of 0.40 minutes of arc (1 degree = … minutes)
A
- There are typically more red cones than green cones, and far fewer blue cones than either of the other two (Getting pictures like this involves impressive optical engineering. The colours are false)
- The spacing of the cones is about 2 micrometers, and corresponds to an angle of 0.40 minutes of arc (1 degree = 60 minutes)
25
Q
Central Visual Pathways
- Optic nerve from each retina divides into L and R halves
- In the optic … L halves from both eyes combine. Similarly R halves.
- Optic tracts relay in the lateral geniculate nuclei of the …
- Part of each optic tract goes to the … colliculus in the mid-brain
- The output of each lateral geniculate goes almost exclusively to the striate cortex in the occipital lobe (V…)
- Here the image of one half of each combined visual field is represented in one half of V….
- The representation of the … region is hugely exaggerated
- Thereafter the cortical input passes on to areas that process depth, motion, colour etc.
A
- Optic nerve from each retina divides into L and R halves
- In the optic chiasm L halves from both eyes combine. Similarly R halves.
- Optic tracts relay in the lateral geniculate nuclei of the thalamus
- Part of each optic tract goes to the superior colliculus in the mid-brain
- The output of each lateral geniculate goes almost exclusively to the striate cortex in the occipital lobe (V1)
- Here the image of one half of each combined visual field is represented in one half of V1.
- The representation of the foveal region is hugely exaggerated
- Thereafter the cortical input passes on to areas that process depth, motion, colour etc.
26
Q
Central Visual Pathways
- Optic nerve from each retina divides into L and R halves
- In the optic chiasm L halves from both eyes combine. Similarly R halves.
- Optic tracts relay in the lateral geniculate nuclei of the thalamus
- Part of each optic tract goes to the superior colliculus in the mid-brain
- The output of each lateral geniculate goes almost exclusively to the striate cortex in the occipital lobe (V1)
- Here the image of one half of each combined visual field is represented in one half of V1.
- The representation of the foveal region is hugely exaggerated
- Thereafter the cortical input passes on to areas that process depth, motion, colour etc.
A
- Optic nerve from each retina divides into L and R halves
- In the optic chiasm L halves from both eyes combine. Similarly R halves.
- Optic tracts relay in the lateral geniculate nuclei of the thalamus
- Part of each optic tract goes to the superior colliculus in the mid-brain
- The output of each lateral geniculate goes almost exclusively to the striate cortex in the occipital lobe (V1)
- Here the image of one half of each combined visual field is represented in one half of V1.
- The representation of the foveal region is hugely exaggerated
- Thereafter the cortical input passes on to areas that process depth, motion, colour etc.
27
Q
Responses of cells in the primary visual cortex (V1)
A
- Combine responses from rows of retinal ganglion cells
28
Q
The visual cortex-columnar organization
- The primary visual cortex (V2, or Brodmann area …) is organized in 3 overlapping patterns:
- 1) Ocular … columns, driven by the left or right eye, but not both
- 2) Smaller … columns in which the orientation of optimal stimuli varies systematically across the surface
- 3) Colour ‘blobs’. Colour information is kept separate from orientation, and passed on to other regions such as V4
- A hypercolumn contains one complete set of everything
A
- The primary visual cortex (V2, or Brodmann area 17) is organized in 3 overlapping patterns:
- 1) Ocular dominance columns, driven by the left or right eye, but not both
- 2) Smaller orientational columns in which the orientation of optimal stimuli varies systematically across the surface
- 3) Colour ‘blobs’. Colour information is kept separate from orientation, and passed on to other regions such as V4
- A hypercolumn contains one complete set of everything
29
Q
The visual cortex-columnar organization
- The primary visual cortex (…, or Brodmann area 17) is organized in 3 overlapping patterns:
- 1) Ocular dominance columns, driven by the left or right eye, but not both
- 2) Smaller orientational columns in which the orientation of optimal stimuli varies systematically across the surface
- 3) … ‘blobs’. … information is kept separate from orientation, and passed on to other regions such as V4
- A hypercolumn contains one complete set of everything
A
- The primary visual cortex (V2, or Brodmann area 17) is organized in 3 overlapping patterns:
- 1) Ocular dominance columns, driven by the left or right eye, but not both
- 2) Smaller orientational columns in which the orientation of optimal stimuli varies systematically across the surface
- 3) Colour ‘blobs’. Colour information is kept separate from orientation, and passed on to other regions such as V4
- A hypercolumn contains one complete set of everything
30
Q
Medical conditions involving the visual pathways in the brain
- Lesion in the optic nerve - just behind eye - blindness of left eye (left eye …)
- Further down past optic chiasm - in the tract where info where left and right info is combined - no vision in one half of visual field - same half of the visual field is absent in both eyes (… …)
- Lesion through optic chiasm - pituitary tumour - no signal processing in the temporal part - parts of the eyes that look outwards in both eyes - just where both eyes look together (… …)
- Lesion of visual cortex itself - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything (…)
A
- Lesion in the optic nerve - just behind eye - blindness of left eye (left eye blindness)
- Further down past optic chiasm - in the tract where info where left and right info is combined - no vision in one half of visual field - same half of the visual field is absent in both eyes (homonymous hemianopa)
- Lesion through optic chiasm - pituitary tumour - no signal processing in the temporal part - parts of the eyes that look outwards in both eyes - just where both eyes look together (bitemporal hemianopa)
- Lesion of visual cortex itself - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything (scotoma)
31
Q
Medical conditions involving the visual pathways in the brain
- Lesion in the optic nerve - just behind eye - blindness of left eye (left eye …)
- Further down past optic chiasm - in the tract where info where left and right info is combined - no vision in one half of visual field - same half of the visual field is absent in both eyes (… …)
- Lesion through optic chiasm - pituitary tumour - no signal processing in the temporal part - parts of the eyes that look outwards in both eyes - just where both eyes look together (… …)
- Lesion of visual cortex itself - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything (…)
A
- Lesion in the optic nerve - just behind eye - blindness of left eye (left eye blindness)
- Further down past optic chiasm - in the tract where info where left and right info is combined - no vision in one half of visual field - same half of the visual field is absent in both eyes (homonymous hemianopa)
- Lesion through optic chiasm - pituitary tumour - no signal processing in the temporal part - parts of the eyes that look outwards in both eyes - just where both eyes look together (bitemporal hemianopa)
- Lesion of visual cortex itself - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything (scotoma)
32
Q
Scotomas
- Lesion of … … itself - scotoma - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything
A
- Lesion of visual cortex itself - scotoma - name that represents a defect in visual field - patient perceive that there is an area of visual field where they can’t see anything
33
Q
Dorsal and ventral streams in the cortex
- The dorsal stream, from occipital to … cortex, is concerned with location, motion and action
- The ventral stream, from occipital to … cortex, is concerned with object (and face) identity, and with conscious perception.
- … in these streams lead to clinical problems
A
- The dorsal stream, from occipital to parietal cortex, is concerned with location, motion and action
- The ventral stream, from occipital to temporal cortex, is concerned with object (and face) identity, and with conscious perception.
- Lesions in these streams lead to clinical problems
34
Q
Dorsal and ventral streams in the cortex
- The dorsal stream, from occipital to parietal cortex, is concerned with …, motion and …
- The ventral stream, from occipital to temporal cortex, is concerned with object (and face) …, and with conscious ….
- Lesions in these streams lead to clinical problems
A
- The dorsal stream, from occipital to parietal cortex, is concerned with location, motion and action
- The ventral stream, from occipital to temporal cortex, is concerned with object (and face) identity, and with conscious perception.
- Lesions in these streams lead to clinical problems
35
Q
Visual agnosia
- In the perceptual matching task the subjects were asked to match the orientation of a card with a slot placed in various ….
- In the “posting” task the subjects had to insert the card into the slot. DF had no difficulty with this, but could not perceptually identify the … of the card.
- The converse condition, in which a patient can describe but not act, is known as optic ….
A
- In the perceptual matching task the subjects were asked to match the orientation of a card with a slot placed in various orientations.
- In the “posting” task the subjects had to insert the card into the slot. DF had no difficulty with this, but could not perceptually identify the orientation of the card.
- The converse condition, in which a patient can describe but not act, is known as optic ataxia.
37
Q
Prosopagnosia
- Is a special case of agnosia, and is the inability to recognise … ….
- It is associated with damage to specific parts of the … lobe
A
- Is a special case of agnosia, and is the inability to recognise familiar faces.
- Oliver sacks was a sufferer, and made the condition famous in 1985 in his book “the man who mistook his wife for a hat”
- It is associated with damage to specific parts of the temporal lobe
38
Q
What is the a special case of agnosia - the inability to recognise familiar faces?
- Oliver sacks was a sufferer, and made the condition famous in 1985 in his book “the man who mistook his wife for a hat”
- It is associated with damage to specific parts of the temporal lobe
A
Prosopagnosia
39
Q
The area most associated with prosopagnosia is the … gyrus, on the underside of the temporal lobe
A
The area most associated with prosopagnosia is the fusiform gyrus, on the underside of the temporal lobe
40
Q
Visual reflexes and their use in medicine
- Vestibulo-ocular reflex (VOR)
- Stabilizes gaze by … movement of the …
- Optokinetic reflex (OKR)
- Stabilizes the image of a moving … on the …
A
- Vestibulo-ocular reflex (VOR)
- Stabilizes gaze by countering movement of the head
- Optokinetic reflex (OKR)
- Stabilizes the image of a moving object on the retina
- Image that moves - object moves - follow movement
41
Q
Visual reflexes and their use in medicine
- …-…. … (VOR)
- Stabilizes gaze by countering movement of the head
- …. … (OKR)
- Stabilizes the image of a moving object on the retina
- Image that moves - object moves - follow movement
A
- Vestibulo-ocular reflex (VOR)
- Stabilizes gaze by countering movement of the head
- Optokinetic reflex (OKR)
- Stabilizes the image of a moving object on the retina
- Image that moves - object moves - follow movement
42
Q
Pupillary reflex
- Normally, if one eye is illuminated both pupils will contract, because both the pretectal nuclei and the … … nuclei receive signals from both eyes.
- Damage to one optic nerve will prevent light in that eye from closing the pupil (direct response), but light in the other eye will still do so (the … response)
- Damage to one … nerve will prevent pupil contraction in that eye, but stimulation of either eye will cause contraction in the pupil in the second eye.
A
- Normally, if one eye is illuminated both pupils will contract, because both the pretectal nuclei and the Edinger Westphal nuclei receive signals from both eyes.
- Damage to one optic nerve will prevent light in that eye from closing the pupil (direct response), but light in the other eye will still do so (the consensual response)
- Damage to one oculomotor nerve will prevent pupil contraction in that eye, but stimulation of either eye will cause contraction in the pupil in the second eye.
43
Q
Pupillary reflex
- Normally, if one eye is illuminated both pupils will contract, because both the … nuclei and the … … nuclei receive signals from both eyes.
- Damage to one optic nerve will prevent light in that eye from closing the pupil (direct response), but light in the other eye will still do so (the consensual response)
- Damage to one oculomotor nerve will prevent pupil contraction in that eye, but stimulation of either eye will cause contraction in the pupil in the second eye.
A
- Normally, if one eye is illuminated both pupils will contract, because both the pretectal nuclei and the Edinger Westphal nuclei receive signals from both eyes.
- Damage to one optic nerve will prevent light in that eye from closing the pupil (direct response), but light in the other eye will still do so (the consensual response)
- Damage to one oculomotor nerve will prevent pupil contraction in that eye, but stimulation of either eye will cause contraction in the pupil in the second eye.
