Term
| What does the visual acuity test determine? |
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Definition
| the maximum distance at which a subject can distinguish between parallel lines and using the principle of “similar triangles” calculate the minimum distance between two images on the retina for them to be separately distinguished. |
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Term
| Give and explain the calculations used in visual acuity |
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Definition
b/a = d/c
If the lines on the visual acuity cards are 2mm apart and the greatest distance at which they can be distinguished is 5.5m and we can assume the distance between the cornea and the retina is 15mm, we can rearrange the equation to find the minimum distance on the retina necessary to distinguish between two points. |
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Term
| What must happen for two lines to be detected as distinct? What is the significance of this? |
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Definition
| the black lines but be detected on two different cones, therefore the maximum distance at which the lines can be distinguished will equate to the width of a single cone on your retina |
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Term
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Definition
| The point at which the optic nerve exits and the blood vessels enter the eye. There are few/no photoreceptors in this region but very little light would pass through blood vessels and axons anyway. |
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Term
| How is a blind spot calculated? |
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Definition
Use similar triangles to calculate the area of the blind spot.
a = distance from eye to paper (mm)
b = diameter of the blind spot on paper (mm)
c =distance from cornea to retina (15mm )
d = unknown |
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Term
| What does the visual field test show? |
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Definition
| This experiment uses a simple technique to map the subjects field of vision for both black and white and colour vision |
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Term
| Explain the differences in the visual field tests for black and white and colour vision |
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Definition
| BW colour field is larger than the colour visual field. The periphery contains mostly rods and is therefore responsible for black and white vision, however, the macula contains mostly cones (colour vision). |
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Term
| What else if the field affected by? |
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Definition
| shape/structure of face as brow and nose obscure detection of stimuli |
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Term
| Explicity, how to the visual fields for B&W and colour compare? |
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Definition
| Visual field is larger for black and white than colour, and elongated toward the temporal side |
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Term
| What effect does light have when it shines on a photoreceptor? |
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Definition
| it is hyper polarised and therefore not releasing glutamate. |
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Term
| What state is a photoreceptor in in the darkness? |
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Definition
| depolarised and therefore releasing glutamate |
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Term
| Describe what events follow when the light shines on a photoreceptor on an ON-CENTRE bipolar cell |
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Definition
1. photoreceptor is hyper polarised and therefore does not release glutamate
2. glutamate does not bind to mGluR6 on the on-bipolar cell and therefore Gi pathway is not activated. The cell is depolarised
3. On bipolar cell releases glutamate which binds to AMPA/Kainate receptors on the On-centre ganglion cell
4. ON centre ganglion cell is depolarised and AP triggered |
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Term
| Describe what events follow when the light does not shine on a photoreceptor on an ON-CENTRE bipolar cell |
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Definition
1. photoreceptor is depolarised
2. glutamate is released from photoreceptor and binds to mGluR6 and hyper polarises the cell
3. Glutamate is not released
4. Firing of on-centre ganglion cell is decreased |
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Term
| Describe what events follow when the light shines on a photoreceptor on an OFF-CENTRE bipolar cell |
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Definition
1. photoreceptor is hyper polarised
2. glutamate is not released and does not bind to AMPA/Kainate receptors on the off-centre bipolar cell
3. off-centre bipolar cell is hyper polarised and does not release glutamate
4. firing of off-centre ganglion cell is decreased |
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Term
| Describe what events follow when the light does not shine on a photoreceptor on an OFF-CENTRE bipolar cell |
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Definition
1. photoreceptor is depolarised and releases glutamate
2. glutamate binds to AMPA/Kainate receptors on off-centre bipolar cell, depolarising it
3. off-centre bipolar cell releases glutamate which binds to AMPA/Kainate receptors on off-centre ganglion cell
4. AP triggered |
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Term
| Draw the retinal responses from a depolarised centre cone |
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Definition
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Term
| Which ganglion cells respond best to colour stimuli? |
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Definition
P-type cells
they have information from either a single cone or a group of the same TYPE of cones (wavelength specific) |
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Term
| Which ganglion cells respond best to moving stimuli? |
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Definition
M cells
fast, transient responses |
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Term
| In the different layers which are M-type and which are P-type? |
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Definition
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Term
| Which layers receive contralateral, and which receive ipsilateral information? |
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Definition
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Term
| What specific deficit leads to red-green colour blindness? |
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Definition
opsin
a total lack = colour blindness |
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