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Theme 2 - 202 > Physiology of Vision > Flashcards

Physiology of Vision Flashcards

1
Q

What two parts of the eye focus an image onto the retina?

A

Cornea and Lens

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2
Q

What can alter the focus of an image?

A

The shape of the lens

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3
Q

Where in the eye is unwanted light absorbed?

A

A pigment layer behind the retina

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4
Q

What can be used to view inside the eye of a patient, and what can be seen?

A

Ophthalmoscope

Optic disc and fovea can be seen

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5
Q

What is the optic disc?

A

Where the optic nerve leaves the eye and also where blood vessels enter/leave the retina.

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6
Q

What ratio of refraction is done by the different parts of the eye?

A
  • 1/3 by the lens

- 2/3 by the cornea

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7
Q

What are refractive errors?

A

Problems with focusing

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8
Q

What are the two types of refractive errors?

A

Hypermetropia and Myopia

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9
Q

What is hypermetropia?

A

Long-sightedness which occurs when the eyeball is either too short or the lens system is too weak.

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10
Q

What is myopia?

A

Short-sightedness which occurs when the eyeball is either too long or too strong.

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11
Q

How can refractive errors be corrected?

A

Via spectacles

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12
Q

What is refractive power measured in?

A

Diopters

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13
Q

How is refractive power (diopters) calculated?

A

Reciprocal of focal length (1 / focal length)

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14
Q

How is the retina structured?

A

Back to front so ganglion cells and blood vessels are in the light path to the photoreceptors (except in the fovea)

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15
Q

How many rods and cones are there, and what type of cells are they?

A

120 million rods and 5 millions cones

They are receptors

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16
Q

What is the difference between rods and cones?

A
  • Rods detect dim light

- Cones detect bright light and colours

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17
Q

How many types go cones are there?

A

3

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18
Q

What is the optic radiation?

A

What carries the output of the lateral geniculate nuclei to the striate cortex

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19
Q

What are the direct layers of the retina?

A
  • Receptors
  • Bipolars
  • Ganglion cells
20
Q

What are the transverse layers of the retina?

A
  • Horizontal cells

- Amacrine cells

21
Q

What is the ganglion cell response?

A

Because ganglion cells respond weakly to changes in overall light intensity, they instead respond to local contrast (light on dark background or dark on light background).

22
Q

What does colourblindness result from?

A

A loss or modification of one (or more) of the three visual cone pigments.

23
Q

The genes for which colour pigments are on the X chromosome?

A

Green and Red

24
Q

The gene for the blue pigment is found in which chromosome?

A

Chromosome 7

25
Q

Is blue colourblindness more rare or less rare than red/green colourblindness, and why is this the case?

A

More rare because it is on chromosome 7 and there are two of them, whilst there is only one X chromosome

26
Q

What is central achromatopsia?

A

A much rarer form of colourblindness which is caused by damage to the cortical colour processing areas (V4)

27
Q

What does the optic nerve from each retina divide into?

A

Into right and left halves

28
Q

What is the optic chiasm?

A

X shaped structure where the two left halves and two right halves from the retinas combine to form optic tracts.

29
Q

What do the optic tracts relay into?

A

The lateral geniculate nuclei of the thalamus

30
Q

What do parts of each optic tract relay into?

A

Superior colliculus of the midbrain

31
Q

Where does the output of each geniculate nuclei go to, and what then happens?

A

The striate cortex, where the input from each half is combined.

32
Q

Where is the striate cortex located?

A

Occipital lobe

33
Q

What are the three overlapping patterns in the primary visual cortex?

A

1) Occular dominance columns
2) Oriental columns (which are smaller)
3) Colour blobs

34
Q

What is a hypercolumn?

A

An area of the primary visual cortex which contains a complete set of all three overlapping patterns

35
Q

What is scotoma?

A

A partial loss of vision (blind spot)

36
Q

What can cause scotoma?

A
  • Lesion in the visual cortex
  • Retinal damage
  • Pressure from a tumour that is restricting the optic nerve, chiasm or tract
37
Q

What are the two streams in the cortex?

A
  • Dorsal Stream: Goes from the occipital lobe to the parietal lobe and is concerned with location, motion and action
  • Ventral Stream: Goes from the occipital lobe to the temporal lobe and is concerned with object/face identity and conscious perception
38
Q

What is prosopagnosia?

A

Inability to recognise familiar faces

39
Q

What causes prosopagnosia?

A

Damage to specific parts of the temporal lobe (usually to fusiform sulcus which is located on the underside of the temporal lobe

40
Q

What is a hemifield?

A

The 170 degree range of vision that one eye can see when facing directly forward

41
Q

What is the vestibulo-occular reflex?

A

When the direction of the eyes remains constant whilst the head is moving

42
Q

What is the optokinetic reflex?

A

When the eye fixes a gaze on a moving object

43
Q

What is the pupillary reflex?

A

The contraction of both pupils when one eye gets illuminated.

This is because the pretactal nuclei and Edinger Westphal nuclei receive signals from both eyes.

44
Q

What would prevent the pupillary reflex?

A

Damage to one of the oculomotor nerves, which would prevent the pupil in the affected eye from contracting.

45
Q

What part of the eye is able to have the clearest vision, and why is this the case?

A

Fovea because it has the highest density of cone cells

Theme 2 - 202 (11 decks)

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