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Neuro > Structure & Function of Eye - Part 2 > Flashcards

Structure & Function of Eye - Part 2 Flashcards

1
Q

Where is the macula in relation to the optic nerve?

A

Temporal (more near the periphery)

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2
Q

Why is there a blind spot?

A

There are no light sensitive cells where the optic nerve meets the retina

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3
Q

What is the other name for the blind spot?

A

Optic disc!

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4
Q

Describe the composition of cells in the fovea. What is the significance of this?

A

High concentration of cones (colour &detail)
Low concentration of rods (light)

Therefore things look brighter out of the corner of your eye than when looked on directly (e.g. stars).

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5
Q

What enables detailed vision?

A

High concentration of cones in the fovea

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6
Q

What results from loss of foveal vision?

A

Poor visual acuity

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7
Q

What are the two types of vision?

A 
Central (foveal, focus) vision 
Peripheral vision (motion)
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8
Q

What does central vision enable?

A

Detailed day vision
Colour vision
Reading (detail)
Facial recognition (detail)

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9
Q

How do you assess central vision?

A

Visual acuity assessment (Snellen test; the one you normally do when you go to the opticians)

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10
Q

What does peripheral vision enable?

A 
Perception of: 
Shape
Movement
Night vision 
Navigation vision
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11
Q

What results from loss of peripheral vision and how is this assessed?

A

Loss of visual field

Visual field assessment

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12
Q

Describe the layers of the retina

A

Outermost layer - photoreceptors (adherent to retinal pigment epithelium)
Middle layer - bipolar cells
Inner layer - retinal ganglion cells (face the light)

Remember light hits the very back of the retina then bounces back to be transmitted into neural signals via optic nerve

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13
Q

What are the first order neurons of the retina and where are they found?

A

Photoreceptors - outermost layer adherent to epithelium of retina

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14
Q

What are the second order neurons of the retina and where are they found?

A

Bipolar cells - middle layer

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15
Q

What do the bipolar cells do?

A

Locally process signals

Regulate and improve contrast sensitivity

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16
Q

Death of retinal ganglion cells is a consequence of what?

A

Raised IOP in glaucoma

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17
Q

What is another word for dim light and which type of retinal cells are adapted to this?

A

Scotopic - rods

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18
Q

What is another word for bright light and which type of retinal cells are adapted to this?

A

Photopic - cones

19
Q

Compare the structure of rods and cones

A

Rods have longer outer segments
Both have connecting cilia
Both have inner segments containing cell organelles

20
Q

Which segment of the photoreceptor is adherent to the retinal pigment epithelium?

A

Outer segment

21
Q

What is synthesized in the inner segment and where is this transported?

A

Photopigments, transported to outer segment disks

22
Q

How do photoreceptors cope with photodamage?

A

They shed distal disks from their tips. This is phagocytosed by retinal pigment epithelium

23
Q

Compare light sensitivity of the photoreceptors

A

Rods are more sensitive to light than cones

24
Q

Compare the speed of response to light of the photoreceptors

A

Rods - slow response but more sensitive to light

Cones - fast response but less sensitive to light

25
Q

How many rods are there?

A

120 million

26
Q

How many cones are there?

A

6 million

27
Q

What do you call the pigmented central region of the retina?

A

Macula or macula lutea

28
Q

How can you assess the fovea and macula clinically?

A

Optical coherence tomography (OCT)

29
Q

What photopigment is found in rods?

A

Rhodopsin

30
Q

What photopigment is found in cones, how many types are there and what is their significance?

A

Photopsin (3 types, react to 3 different light frequencies)

31
Q

What are the three types of cones?

A

Blue, red and green

32
Q

Which cone sees blue?

A

S- cone (sky)

33
Q

Which cone sees green?

A

M cone (meadow)

34
Q

Which cone sees red?

A

L cone (love)

35
Q

What is the most common type of vision deficiency? Explain this and which colours get confused.

A

Deuteranomaly - M cone frequency shift from green to red (good to bad), causing red-green confusion

36
Q

What do you call malfunctioning S cones?

A

Tritanomaly

37
Q

What do you call malfunctioning L cones?

A

Protanomaly

38
Q

What do you call it when all three cones malfunction?

A

Anomalous trichromatism

39
Q

What do you call it when each cone is missing?

A

M missing - Deuteranopia
S - Tritanopia
L - Protanopia

40
Q

What do you call black and white vision?

A

Achromatopsia

41
Q

Describe the colour blindness test and what it looks for

A

ISHIHARA TEST
Red and green circles arranged in a pattern, such as a number. Deuteranomaly patients wouldn’t be able to see any pattern, or recognize the wrong pattern.

42
Q

Describe adaption to the dark

A

In the dark, our sensitivity to light increases. It’s a biphasic process:

Rod’s take 30 mins to adapt to the light (to produce rhodopsin)
Cones take 7 minutes to adapt

43
Q

Describe adaption to the light

A 
Happens in 5 minutes
Bleaching of photopigments 
Neuro-adaptation 
Inhibition of rod/cone function?
Pupil constriction
44
Q

What happens when light falls onto the retina?

A

Dissociation of trans-retinal and opsin

Neuro (11 decks)

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