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Z YEAR 2 BRS NEURO > Visual System 1.5 > Flashcards

Visual System 1.5 Flashcards

1
Q

What is the retina?

A

Very thin layer of tissue that lines the inner part of the eye

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2
Q

What is the retina responsible for?

A
  1. capturing the light rays that enter the eye

2. these light impulses are then sent to the brain for processing, via the optic nerve.

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3
Q

What does the optic nerve do?

A

transmits electrical impulses from the retina to the brain

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4
Q

Where does the optic nerve connect?

A

to the back of the eye near the macula

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5
Q

What is the visible portion of the optic nerve called?

A

optic disc (corresponding anatomic landmark for physiological blind spot)

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6
Q

Where is the blind spot?

A

Where the optic nerve meets the retina there are no light sensitive cells

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7
Q

Where is the macula?

A

roughly in the centre of the retina, temporal to the optic nerve

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8
Q

What is the macula?

A
  • small and highly sensitive part of the retina responsible for detailed central vision
  • allows us to appreciate detail and perform tasks that require central vision such reading
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9
Q

What is the fovea?

A

the very centre of the macula and most sensitive part of retina

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10
Q

What is the concentration of rods and cones in the fovea?

A
  • Highest conc of cones

- Lowest conc of rods

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11
Q

What is central vision?

A
  • Detail day vision, colour vision

- Reading, facial recognition

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12
Q

How do you asses central visions?

A

visual acuity assessment

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13
Q

What does loss of foveal vision lead to?

A

Poor visual acuity

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14
Q

What is perisperhal vision?

A
  • Shape, movement, night vision

- Navigation vision

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15
Q

How is peripheral vision assessed?

A

by visual field assessment

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16
Q

What happens if there is is extensive loss of visual field?

A

unable to navigate in environment, patient may need white stick even with perfect visual acuity

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17
Q

What is the outer layers of the retinal structure?

A
  • Photoreceptors (1st order neuron)

- Detection of Light

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18
Q

What is the middle layer of retinal structure?

A
  • Bipolar Cells (2nd order neuron)

- Local signal processing to improve contrast sensitivity, regulate sensitivity

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19
Q

What is the inner layer of retinal structure?

A
  • Retinal ganglion cells (3rd order neuron)

- Transmission of signal from the eye to the brain

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20
Q

What does the retina form?

A

the innermost layer of the coat of eye in the posterior segment

21
Q

What does the retina consist of?

A
  • an outer thin layer of Retinal Pigment Epithelium, situated right in front of the Choroid,
  • inner thicker layer called the Neuroretina.
22
Q

What does the retinal pigment epithelium do?

A

transports nutrient from the choroid to the photo-receptor cells,
and removes metabolic waste from the retina

23
Q

What is the neuroretina made up of?

A

photo-receptors and neurons

24
Q

What are the layers of retina?

A
  1. Outer Layer consisting of photo-receptors,
  2. middle layer of intermediate neurons
  3. inner layer of ganglion nerve cells
    - axon running along the optic nerve into the brain
25
Q

What are rods?

A
  1. Longer outer segment with photo-sensitive pigment
  2. 100 times more sensitive to light than cones
  3. Slow response to light
  4. Responsible for night vision (Scotopic Vision)
    120 million rods
26
Q

What are cones?

A
  1. Less sensitive to light, but faster response
  2. Responsible for day light fine vision and colour vision (Photopic Vision)
    6 million cones
  3. Shorter outer segment
27
Q

Where are photopigments synthesised?

A

inner photo-receptor segment,

and are then transported to the outer segment

28
Q

What is the outer segment made of?

A

stacks of discs

29
Q

What are distal discs?

A

The distal discs with deactivated photo-pigments are shedded from the tips,
and phago-cytosed by the retinal epithelial cells

30
Q

What happens to the deactivated photopigments?

A

The deactivated photopigments are regenerated inside the retinal epithelial cells, and then transported back to the photo-receptors

31
Q

What is rod (scotopic) vision?

A
  1. Peripheral and night vision
  2. More photoreceptors
    3, More pigment
  3. Higher spatial and temporal (time) summation
  4. Recognizes motion
32
Q

What is cone (photic) vision?

A
  • Central and day vision

- Recognizes colour and detail

33
Q

Where is rod density highest?

A

Rod photo-receptors are widely distributed all over the retina,
with the highest density just outside the macula (tails off towards periphery)

34
Q

Are rod photoreceptors in the macula?

A

NO

35
Q

Where are cone photoreceptors?

A

distributed only within the macula

36
Q

Where can you find the highest conc of rod photoreceptors in retina?

A

20-40 degrees away from fovea

37
Q

Where is the peak light sensitivity for rod vision?

A

498 nano-meters wavelength

38
Q

What are the different cones and colours?

A

S-Cones: Blue (short wavelength)
M-Cones: Green
L- Cones: Red (long wavelength)

39
Q

What is yellow light?

A
  1. wavelength between the peak sensitivity wavelengths of M-Cones and L-Cones.
  2. Yellow light stimulates both M-cones and L-cones equally.
  3. Biologically, we experience yellow light as a combination of green and red light.
40
Q

What is the commonest form of colour vision deficiency?

A

Deuteranomaly

41
Q

What is deuteranomaly caused by?

A

shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion - don’t perceive red

42
Q

What is the name for full colour blindness?

A

achromatopsia

43
Q

What is the prevalence of colour vision deficit?

A

8% amongst males,

and 0.5% amongst females

44
Q

What is anomalous trichromatism?

A

Colour Vision deficits can be caused by a shift in the photo-pigment peak sensitivity

45
Q

What is commonest form of anomalous trichromatism?

A

Deuteranomaly

46
Q

What is dichromatism?

A

only two cone photo-pigment sub-types are present

47
Q

What is monochromatism?

A

complete absence of colour vision

48
Q

What is blue cone monochromatism?

A
  • presence of only blue L-cones

- normal day light visual acuity

49
Q

What is rod cone monochromatism?

A
  • total absence of all cone photo-receptors

- no functional day vision

Z YEAR 2 BRS NEURO (21 decks)

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