Hypermetropia - long sightedness: Eyeball too short or lens system too weak

Myopia - short sightedness: - more common than hypermetropia (long) Eyeball too long or lens system too strong

Physiology of Vision Flashcards by Chrissy Taaffe

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

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

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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

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

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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)

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)

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The … does 2/3 of the ray bending
The … does the other 1/3, but also allows the focus to vary (Accommodation)

The cornea does 2/3 of the ray bending
The lens does the other 1/3, but also allows the focus to vary (Accommodation)

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The cornea does 2/3 of the ray bending
The lens does the other 1/3, but also allows the focus to vary (…)

The cornea does 2/3 of the ray bending
The lens does the other 1/3, but also allows the focus to vary (Accommodation)

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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.

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.

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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.

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.

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Hypermetropia = …

Hypermetropia - long sightedness:
Eyeball too short or lens system too weak

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Myopia = …

Myopia - short sightedness: - more common than hypermetropia (long)
Eyeball too long or lens system too strong

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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

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

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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

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

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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 …

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.

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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

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

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Rhodospin is the photosensitive pigment in the …

Rhodospin is the photosensitive pigment in the rods

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Rhodospin is the photosensitive pigment in the …

Rhodospin is the photosensitive pigment in the rods

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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.

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.

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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

Red cone - 560nm
Green cones - 530 nm
Blue cones - 420 nm
Rods - 500nm
Rods not on diagram - Peak sensitivity of about 500nm

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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)

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)

Colour blindness

Colour blindness results from a loss or modification of one or more of the three cone visual pigments (cone opsins)
- The genes for the red and green pigments are on the X chromosome and damage to one of these genes results in red/green colour blindness.
- Males have only one X chromosome, but females have two (i.e. an intact spare) which is why red/green colour blindness is much more common in males (…%, versus …% in females)
- The blue pigment gene is on chromosome 7, which is paired in both sexes. Blue colour blindness is consequently much … than red/green.
There is another, much rarer kind of colour blindness, which has nothing to do with the pigments, but is caused by damage to the cortical colour processing areas (V4). This is known as central ….

Colour blindness results from a loss or modification of one or more of the three cone visual pigments (cone opsins)
The genes for the red and green pigments are on the X chromosome and damage to one of these genes results in red/green colour blindness.
Males have only one X chromosome, but females have two (i.e. an intact spare) which is why red/green colour blindness is much more common in males (7%, versus 0.5% in females)
The blue pigment gene is on chromosome 7, which is paired in both sexes. Blue colour blindness is consequently much rarer than red/green.
There is another, much rarer kind of colour blindness, which has nothing to do with the pigments, but is caused by damage to the cortical colour processing areas (V4). This is known as central achromatopsia.

What is central achromatopsia?

There is another, much rarer kind of colour blindness, which has nothing to do with the pigments, but is caused by damage to the cortical colour processing areas (V4).

… colour blindness is consequently much rarer than …/…

Blue colour blindness is consequently much rarer than red/green.

Colour blindness results from a loss or modification of one or more of the three cone visual … (cone opsins)

Colour blindness results from a loss or modification of one or more of the three cone visual pigments (cone opsins)

The genes for the red and green pigments are on the X chromosome and damage to one of these genes results in red/green colour blindness. therefore more common in what gender?

Males have only one X chromosome, but females have two (i.e. an intact spare) which is why red/green colour blindness is much more common in males (7%, versus 0.5% in females)

The visual cortex is the primary cortical region of the brain that receives, integrates, and processes visual information relayed from the …. It is in the … lobe of the primary … cortex, which is in the most … region of the brain.

The visual cortex is the primary cortical region of the brain that receives, integrates, and processes visual information relayed from the retinas. It is in the occipital lobe of the primary cerebral cortex, which is in the most posterior region of the brain.

_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.

* 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.

_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.

_Responses of cells in the primary visual cortex (V1)_

* Combine responses from rows of retinal ganglion cells

_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

* 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

_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

* 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

_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 (...)

* 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)

_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

* 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

_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

* 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

_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

_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 ....

* 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.

Ventral stream - issue with ...

**Ventral stream - issue with perception**

_Prosopagnosia_ * Is a special case of agnosia, and is the inability to recognise ... .... * It is associated with damage to specific parts of the ... lobe

* 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

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

Prosopagnosia

The area most associated with prosopagnosia is the ... gyrus, on the underside of the temporal lobe

The area most associated with prosopagnosia is the fusiform gyrus, on the underside of the temporal lobe

_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 ...

* 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

_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

_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.

* 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.

_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.