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The nervous system > Vision 1 + 2 > Flashcards

Vision 1 + 2 Flashcards

1
Q

What process underpins the eye projecting a sharp image onto the retina

A

Refraction

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2
Q

What is refraction

A

bending of light rays when it passes from one optical medium to another

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3
Q

A biconvex lens bends an incoming beam of light and converges or diverges the light rays

A

Converges them to one specific point

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4
Q

A biconcave lens bends an incoming beam of light and converges or diverges the light rays

A

Diverges them to several points

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5
Q

Anatomical components of the eye that are involved in refraction (4) + which 2 of these are the main components responsible for refracting light

A

Cornea - main
Lens - main
Aqueous humor
Vitreous humor

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6
Q

If an object is far away, only the … rays from the object hit the cornea, … rays wouldn’t hit the cornea therefore less … … is needed to invert the image onto the retina

A

parallel

divergent

bending power

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7
Q

If an object is up close, the … rays from the object hit the cornea as well as the … rays, however the … rays need extra … … to form an inverted image on the retina

A

divergent

parallel

bending power

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8
Q

Does the lens become thicker with constant viewing of close or distant objects

A

Close

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9
Q

Is the cornea or the lens a more powerful ‘bender’ of light

A

Cornea

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10
Q

Anything beyond 6m of vision is considered

A

infinity

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11
Q

Define accommodation in respect to the eye

A

When the eyes change focus from a distant to a close object

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12
Q

What 3 things occur to allow accommodation of the eye

A

Lens changes shape - becomes more spherical & thicker

Pupils constrict - to sharpen focus

Eyes converge

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13
Q

How does ciliaris contraction cause the lens to become thicker + more spherical (4)

A

Ciliaris contraction makes the ciliary body bulge out –> which decreases the space between the 2 ciliary bodies –> suspensory ligaments therefore become loose/lax so decreasing the pull on the lens –> lens no longer under stretch so becomes THICKER + MORE SPHERICAL

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14
Q

Are the lateral or medial recti thicker

A

Medial

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15
Q

What is myopia

A

Short sightedness (i.e. need glasses to see distance)

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16
Q

What is hyperopia

A

Long sightedness (i.e. need glasses to read a book)

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17
Q

What is presbyopia

A

Normal loss of near focusing ability that occurs with age

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18
Q

Pathophysiology of myopia (Short sighted)

  • is eyeball too short or long AP
  • why are distant objects blurry
  • what is wrong with the shape of the cornea
A

too long

blurry because light rays are refracted (bent) TOO MUCH by the cornea + lens –> focusing an image IN FRONT OF THE RETINA instead of on the retina

cornea too curved so refractive power of cornea and lens combined is too much for the length of the eyeball

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19
Q

What is emmetropia

A

Perfect sight

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20
Q

Do myopes have excessive or not enough refractive power

A

Excessive

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21
Q

How does the excessive refractive power of myopes work to their advantage compared to emmetropes

A

With a close object, the light rays coming from it are divergent which allows the excessive refractive power to come to use –> forms an image on the retina without needing to increase lens curvature (WITHOUT USING ACCOMODATION) whereas emmetropes would have to use accommodative powers

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22
Q

Symptoms/signs of myopes (short sighted) (2)

A

Headache when looking at distant objects

Divergent squint - one eye abducted, the other normal (in infants)

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23
Q

Correction of myopia

  • what needs to be done to bending power
  • management options (2)
A

Bending power needs to be decreased so want to use a lens that diverges light rays

Biconcave lens (glasses or contacts)
or
Laser eye surgery

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24
Q

Pathophysiology of hyperopia (long sighted)

  • is eyeball too short or long AP
  • what is wrong with the lens
  • why are close objects blurry (5)
A

Too short

lens too flat

Light rays of distant objects are not refracted enough by the cornea + lens –> so image is focused BEHIND THE RETINA –> hypermetropes then automatically start to use their ACCOMODATIVE POWER to make lens thicker to allow the image of the distant object to form on the retina (which normally doesn’t need to be used) –> effectively lose/use up one’s accommodative power

So, when hypermetropes then need to see close objects, don’t have any accommodative power to do this

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25
Q

Symptoms (1) /signs (1) of hyperopia

A

Eye strain after reading/looking at screen for too long

Convergent squint - one eye adducted, the other normal (in infants)

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26
Q

Correction of hyperopia

  • what needs to be done to bending power
  • management options (2)
A

Bending power needs to be INCREASED

Biconvex lens (to converge the light rays into one point, allowing accommodative power to rest) - glasses, contacts
or
Laser eye surgery

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27
Q

What is astigmatism + what sight is affected

A

NON-SPHERICAL CURVATURE OF CORNEA/ LENS

Both short and long sight affected

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28
Q

Pathophysiology of astigmatism

A

Corneal surface has different curvatures in different meridians so the refraction of light rays along one axis is not the same as that of the other axis

One meridian is flatter than the other so light rays will refract slightly more on one meridian than the other

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29
Q

Symptoms of astigmatism (2)

A

Headache

Eye strain

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30
Q

Correction of astigmatism (3)

A

Needs special type of lens that contain different refractive powers at different meridians

Cylindrical lens (correct the difference between the refractive powers of the 2 principal meridians [vertical + horizontal])
or
Toric lens - special contact lenses, ring donut shape
or
Laser eye surgery

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31
Q

What are toric lenses (3 components that allow it to work) and what are they used for

A

special contact lenses used for astigmatism, not the typical spherical shape but a torus shape (ring donut shape)

Contain a sphere power (to correct myopia/hyperopia), cylinder power and an axis designation (enables them to rotate into position so that the meridians of power are lined up with the meridians of your eyes)

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32
Q

Pathophysiology of presbyopia (lose short sightedness due to old age)

A

As you age, lens gets less mobile/elastic and more RIGID (as collagen fibres become more rigid)

So, when ciliaris contracts, lens is not as capable as before to change shape (to change spherical) (LOSE ACCOMODATIVE POWERS)

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33
Q

Correction of presbyopia

A

Biconvex lens - to increase refractive power

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34
Q

What is phototransduction

A

conversion of light energy to an electrochemical response by photoreceptors

35
Q

How is light energy converted into a neural signal

A

light energy stimulates photoreceptors (rods and cones) –> cascade reactions which hyper polarises the rods and cones creating an electrical impulse –> transmitted to CN II from retina –> becomes an AP in the nerve

36
Q

What part of rods and cones do light waves activate (2)

A

light waves activate the OUTER SEGMENT of rods and cones (photoreceptors) which is made up of stacks of lamellae

Integrated into the cell membrane of these lamellae are VISUAL PIGMENTS - rhodopsin and opsin

37
Q

What is the visual pigment of

  • rods
  • cones
A

Rhodopsin

Opsin

38
Q

Rhodopsin is aka + component parts (2)

A

visual purple

opsin (colourless protein) + 11-cis retinal (vitamin A compound)

39
Q

How is vitamin A involved in phototransduction (3)

Hint: conformation change, bleaching

A

When eye is exposed to light, the 11-cis retinal component (vitamin A derived compound) of rhodopsin converts into all-trans retinal which means rhodopsin undergoes a conformational shape

The change in conformation initiates a phototransduction cascade within the rod, whereby light is converted into an electrical signal (AP) that is then transmitted along the optic nerve to the visual cortex.

The change in conformation also causes opsin to dissociate from retinal because all-trans retinal can’t fit inside the opsin protein –> resulting in bleaching

40
Q

What is bleaching and how does it affect vision

A

Bleaching is when opsin dissociates from retinal because all-trans retinal can no longer fit inside the opsin protein

Bleaching limits the degree to which the rods are stimulated, decreasing their sensitivity to bright light and allowing cone cells to mediate vision in bright environments

41
Q

The change in conformation of rhodopsin after being exposed light also causes opsin to dissociate from retinal because all-trans retinal can’t fit inside the opsin protein (bleaching), however the retina needs to be ‘unbleached’ or else we wouldn’t be able to see after 5 mins

So how do we ‘unbleach’ the retina

A

Need to constantly convert all-trans retinal BACK TO 11-cis retinal (regenerating visual pigment) which requires energy in the form of vitamin A (taken from vitamin A stores in liver)

42
Q

What’s more abundant - rods or cones

A

rods

43
Q

Signs of vitamin A deficiency (3)

A

Bitot’s spots (in conjunctiva)
Corneal ulceration
Corneal opacification

44
Q

Colour blindness is due to a defect of what

A

Cones

45
Q

Gold standard investigation of glaucoma

A

Automated perimetry

46
Q

Describe the path the electrical signal takes from the retina to the visual cortex

A

Optic nerve –> optic chasm –> optic tract –> lateral geniculate body –> optic radiation –> visual cortex

47
Q

What sits under the optic chiasm

A

Pituitary gland

48
Q

What is the optic tract

A

axons/fibres of the optic nerve

49
Q

Fibres of the optic tract synapse where

A

LGB

50
Q

At the optic chiasm, what fibres cross over

A

Medial/nasal fibres cross over (which view the temporal field)

51
Q

Optic tract contains fibres from … (2)

A

(lateral) temporal half of the ipsilateral eye

crossed-over nasal fibres from the contralateral eye

52
Q

Right visual cortex sees the ….

A

left visual field

53
Q

Left visual field is composed of what fibres (2)

A

LEFT NASAL RETINAL NERVE FIBRES and RIGHT TEMPORAL RETINAL NERVE FIBRES

54
Q

Right visual field is composed of what fibres (2)

A

RIGHT NASAL RETINAL NERVE FIBRES and LEFT TEMPORAL RETINAL NERVE FIBRES

55
Q

Define a tract

A

Bundle of myelinated axons creating a nerve fibre pathway

56
Q

LGB is part of what

A

Thalamus

57
Q

Nasal retinal nerve fibres view what field

A

Temporal

58
Q

Temporal retinal fibres view what field

A

Nasal

59
Q

If R optic nerve damaged, what happens

A

Blindness in R eye because no signal from right eye passed back to visual cortex

60
Q

Disruption of optic chiasm causes what

A

Bitemporal hemianopia

61
Q

If R optic tract damaged, what happens

A

Contralateral homonymous hemianopia - can’t see nasal field in R eye and temporal field in L eye

62
Q

If right optic radiation damaged, what happens

A

Same as damage to R optic tract

Contralateral homonymous hemianopia - can’t see nasal field in R eye and temporal field in L eye

63
Q

Binocular vision allows good perception of what, whereas uniocular vision doesn’t

A

Depth

64
Q

What axis are extrinsic ocular muscles attached along

A

Orbital axis, not optical axis

-orbital axes are not parallel to each other, optic axes are

65
Q

When the eye is ABDUCTED,

  • what muscle elevates
  • what muscle depresses
  • what muscle intorts
  • what muscle extorts
A

SR
IR
SO
IO

66
Q

When the eye is ADDUCTED,

  • what muscle elevates
  • what muscle depresses
  • what muscle intorts
  • what muscle extorts
A

IO
SO
SR
IR

67
Q

What is strabismus

A

Squint eyes

-one of the eyes may turn in, out, up or down while the other eye looks ahead

68
Q

What is esotropia

A

Convergent squint (cross eyed)

69
Q

What is exotropia

A

divergent squint (one or both eyes turn outwards)

70
Q

What is amblyopia

A

Lazy eye

  • childhood condition where an eye fails to achieve normal visual acuity (vision doesn’t develop properly), even with glasses
  • eye and brain not working well together
71
Q

What can be attempted to correct amblyopia in the early years

A

patching of the “good” eye to force the brain to pay attention to the visual input from the amblyopic eye and enable normal vision development to occur in that eye

72
Q

Consequences of strabismus (Squint)

A

Amblyopia

Diplopia

73
Q

Increased light to pupil stimulates sympathetic or parasympathetic –> pupils subsequently dilate or constrict

A

Parasympathetic

Constrict

74
Q

Decreased light to pupil stimulates sympathetic or parasympathetic –> pupils subsequently dilate or constrict

A

Sympathetic

Dilate

75
Q

Usually, visual impulses travelling along the optic nerve –> optic chiasm –> optic tract ultimately synapse at the LGB, however fibres destined to activate the pupillary light reflex DO NOT GO TO THE LGB - where do they synapse instead (essentially asking about AFFERENT pathway of the pupillary light reflex)

A

Leave the optic tract to go to synapse at the CN III nucleus in the midbrain, specifically the edinger-westphal (EWN) nucleus

76
Q

The edinger-westphal nucleus (EWN) is part of the nucleus of what CN

A

CN III

77
Q

Describe the EFFERENT pathway of the pupillary light reflex

A

Once synapsed in the edinger-westphal nucleus (EWN), parasympathetic fibres pass through CN III into the orbit and synapse at the ciliary ganglion –> ultimately constricting pupils

78
Q

Define anisocoria

A

Pupils are different sizes

79
Q

Name 2 common pupil abnormalities

A

Anisocoria

Abnormal light reflex

80
Q

Common causes of abnormal pupillary reflex (3)

A

Retinal disease, e.g. retinal detachment
CN II disease, e.g. optic neuritis
CN III disease

81
Q

In CN III palsy, there’s usually no damage to sympathetic or parasympathetic fibres so pupils should still …

A

Parasympathetic

constrict

82
Q

pupillary reflex should still be present in CN III palsy, if absent it’s unlikely to be CN III palsy and could possibly be due to …

A

cerebral artery aneurysm

83
Q

What is Horner’s syndrome

A

Anisocoria due to damage of the sympathetic innervation to the pupil (i.e. innervation of dilator pupillae)

84
Q

Horner’s syndrome presentation triad

A

Miosis
Ptosis
Anhidrosis - loss of sweating on affected side

The nervous system (9 decks)

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