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Systems: Neurology AB > Vision 1 > Flashcards

Vision 1 Flashcards

1
Q

Refraction in the eye

A

Light rays bend to form a sharp image on the retina

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2
Q

Accommodation

A

We can focus on far off or near objects by changing how much we bend the light rays

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3
Q

Refractive errors

A

Sometimes there is a mismatch between how much we bend light rays

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4
Q

Refraction

A

Bending of light when it passes from one optical medium to another

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5
Q

What is transparent to allow light to fall on the retina?

A
  • Cornea
  • Aqueous humor
  • Lens
  • Vitreous humor
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6
Q

What are the 2 main areas of bending of light?

A

The cornea is the most powerful bender of light (45D) but the lens (15D) has the capacity to change its bending power

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7
Q

What happens to the lens as an object comes closer?

A

The eye needs more bending power to focus on the object, therefore the lens becomes thicker and hence more powerful.

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8
Q

What accommodative power does our eyes have?

A

To change focus from distant objects (infinity) to close objects (20cm)

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9
Q

What are the 3 components of accommodation?

A
  • Lens changes shape
  • Pupil constricts
  • Eyes converge
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10
Q

What shape change does the lens undergo during accommodation?

A

Becomes thicker and more spherical

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11
Q

Why does ciliary body contraction result in the ability to focus on close objects?

A
  • Ciliary body contraction (parasympathetic) causes lens to become thicker and more spherical
  • A thicker lens is more powerful: can focus close objects
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12
Q

How does the lens become thicker?

A
  • Ciliary muscle contracts making the ciliary body bulge
  • Space in the middle decreases
  • Suspensory ligaments become lax
  • Lens is no longer under stretch
  • Lens becomes thicker
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13
Q

Why does the pupil constrict when focussing on a close object?

A

We require a sharp focus

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14
Q

How is a sharp focus created?

A

Pupillary constriction to allow only a few rays (those from the object) to pass through

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15
Q

What muscle is responsible for constriction of the pupil?

A

Pupillary constrictor (sphincter pupillae) is a concentric muscle around the border of the pupil which gets parasympathetic innervation

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16
Q

What muscles are responsible for convergence of our eyes?

A

We use our medial rectus of both eyes to converge

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17
Q

Why are our medial recti thicker than our lateral recti muscles?

A

Humans spend a lot of time doing close work

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18
Q

Convergence

A

Turning inwards of our eye to focus on a close up object

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19
Q

Myopia

A

Short sightedness

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20
Q

Hyperopia

A

Long sightedness

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21
Q

Astigmatism

A

Non-spherical curvature of cornea(or lens)

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22
Q

Presbyopia

A

Long sightedness of old age

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23
Q

Give 4 examples of refractive errors.

A
  • Myopia
  • Hyperopia
  • Astigmatism
  • Presbyopia
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24
Q

Emmetropia

A

Perfect vision

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25
Q

Describe myopic vision.

A
  • Close objects look clear
  • Distant objects appear hazy
  • Image formed short of the retina
26
Q

What is the most common cause of myopia?

A

Eyeball is too long

27
Q

Why can people with myopia see close up objects clearly?

A
  • The bending power of the cornea and lens is too much
  • Therefore, when an object is brought closer the rays coming from it are divergent and then this bending power comes to use
28
Q

What are the symptoms of myopia?

A
  • Headaches
  • Complain of not being able to see the board at school
  • Divergent squint in infants and preverbal children
  • Loss of interes in sports/ people with greater interest in books and pictures in toddlers
  • Teachers may notice child losing interest in class
29
Q

What is the treatment for myopia?

A

The bending power needs to be decreased by biconcave lenses

  • Spectacles
  • Contact lenses
  • Laser eye surgery
30
Q

Describe hyperopic vision.

A
  • Close objects look hazy
  • Distant objects appear clear
  • Image formed behind retina
31
Q

What are the main causes of hyperopia?

A
  • Eyeball too short

- Lens too flat

32
Q

Why are longsighted people unable to see close up objects?

A
  • They automatically start to use up their accommodative power to see far away things.
  • They use more and more of this power up as the object moves closer until there is no more accommodative power
  • Therefore the find it difficult to see clos up objects
33
Q

What are the symptoms of hyperopia?

A
  • Symptoms of eyestrain after reading/working on computer in the young
  • Convergent squint in children/toddlers
34
Q

If a child has a convergent squint what must be done?

A

Immediate correction to preserve vision in both eyes and prevent a lazy eye

35
Q

What is the treatment for hyperopia?

A

Biconvex glasses alleviates use of glasses for focussing distant objects and rests the power for accommodative power

  • Contact lenses
  • Laser eye surgery
36
Q

Describe astigmatic vision.

A

Close and distant objects appear hazy

37
Q

Why is the image formed always hazy in astigmatism?

A
  • Surface has different curvatures in different medians
  • So the bending of light rays along one axis will never be the same as that of the other axis
  • Therefore image is always hazy
38
Q

What is the treatment for astigmatism?

A

Cylindrical glasses

  • Laser eye surgery
  • Toric contact lenses
39
Q

What causes presbyopia?

A
  • With age the lens gets less mobile/elastic
  • So when the ciliary muscle contracts it is not as capable as before to change shape
  • Therefore it becomes difficult to see near objects
40
Q

When does presbyopia usually occur?

A

Around about the 5th decade

41
Q

How is presbyopia treated?

A

Biconvex glasses

42
Q

What kind of wave is visible light?

A

Electromagnetic

43
Q

What does the energy in light waves need to stinumlate?

A

Photoreceptor cells on the retina

44
Q

Phototransduction

A

The conversion of light energy to an electrochemical response by the photoreceptors

45
Q

What cells in the human eye are the photoreceptors

A

Rods and cones

46
Q

What do the phototransduced rods and cones need to activate?

A

Optic nerve neurons to generate an action potential

47
Q

Describe the structure of rod and cone cells.

A
  • Synaptic terminal
  • Axon
  • Nucleus forming (outer nuclear layer of retina)
  • Inner segment containing cell organelles
  • Outer segement containg discs/ lamellae
48
Q

What is each lamellae made up of?

A

Cell membrane

49
Q

What is integrated into the cell membrane of the lamellae?

A

The visual pigment rhodopsin in rods and opsins S,M and L in cones

50
Q

How do opsins and rhodopsins differ?

A

In their spectral sensitivity

51
Q

What happens to 11-cis retinal when light falls on it?

A

Isomerises to all-trans retinal

52
Q

The chromophore nesting in the posit is formed from what?

A

Dietary vitamin A

53
Q

What is rhodopsin formed from?

A
  • Opsin

- 11-cis retinal

54
Q

How does bleaching of the visual purple occur?

A

-All trans retinal cannot fit into the opsin so rhodopsin splits resulting in bleaching

55
Q

How does bleaching of the visual pigment result in photo transduction?

A

Phototransduction cascade

56
Q

What role does vitamin A play in the visual pigment?

A

Visual pigment regeneration

57
Q

How do the photoreceptors differ form other cells in the body?

A

When at rest (in the dark) they are kept in a depolarised state by open Na/Ca channels

58
Q

If there is not a constant supply of vitamin A what will be former?

A

Retinyl esters

59
Q

What will any condition affecting vitamin A absorption result in?

A
  • Affect vision: night blindness

- Essential for healthy epithelium so can cause abnormalities in conjunctiva and corneal epithelium

60
Q

What conditions can vitamin A deficiency occur in?

A
  • Malnutrition

- Malabsorption syndromes such as coeliac disease, sprue

61
Q

What is sometimes the first indication of vitamin A deficiency?

A

Bitot’s spots in the conjunctiva

Systems: Neurology AB (51 decks)

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