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visual system Flashcards

1
Q

what is the lacrimal system responsible for

A

tears - basal, reflex and emotional (crying)

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2
Q

how are tears produced

A

produced by lacrimal gland
drain through two puncta, openings on medial lid margin
flow through superior and inferior canaliculi
gather in tear sac- exit through tear duct into nasal cavity

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3
Q

what is the lacrimal systems afferents

A

cranial nerve, V1 - Opthalmic trigeminal

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4
Q

what are the efferents in lacrimal system

A

parasympathetic

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5
Q

what are the neurotransmitters involved in lacrimal system

A

acetylcholine

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6
Q

what is the role of the tear film

A

mains smooth cornea
oxygen supply to cornea - normal cornea has no blood supply
removal of debris
bactericide

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7
Q

what are the 3 layers in tear film

A

superficial lipid layer - reduce tear film evaporation(produced by meibomian glands
aqueous water layer
mucinous layer - maintains surface wetting

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8
Q

what is conjunctiva

A

thin transparent tissue that covers outer surface of eye

  • begins at outer edge of cornea, covers visible part of eye and lines inside of eyelids
  • nourished by tiny blood vessels
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9
Q

what are the 3 layers/coats of eye

A

scalera - hard and opaque
choroid - pigmented and vascular
retina - neurosensory tissue

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10
Q

what is the scalera

A

aka ‘white of the eye’
tough, opaque tissue that serves as eyes protective outer coat
high water content

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11
Q

what is the cornea

A

transparent, dome shaped window covering front of eye
low water content
powerful refracting surface - providing 2/3 of eyes focusing power

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12
Q

what are the 5 layers of the cornea

A
  1. epithelium
  2. bowmans membrane
  3. stroma - regularity contributes towards transparency
  4. descemets membrane
  5. endothelium - pumps fluid out cornea and prevents corneal oedema
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13
Q

what is the uvea

A

vascular coat of eyeball and lies between sclera and retina
composed 3 parts: iris, ciliary body and choroid
- intimately connected and disease of one part also affects other portions though not necessarily to same degree

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14
Q

what is the choroid

A

lies between retina and scalera

composed layers of blood vessels that nourish back of eye

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15
Q

what is the iris

A

controls light levels inside eye similar to aperture on camera
round opening- pupil
embedded with tiny muscles that dilate and constrict

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16
Q

what is structure of the lens

A

outer acellular capsule
regular inner elongated cell fibres -
may lose transparency with age - cataract (clouding)

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17
Q

what is the function of the lens

A 
transparency
regular structure
refractive power
1/3 of eye focusing power - higher refractive index than aqueous fluid and vitreous
accommodation
elasticity
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18
Q

what is the retina

A

very thin layer of tissue that lines inner part of eye
- responsible for capturing light rays that enter the eye
light impulses are sent to brain for processing via optic nerve

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19
Q

what is optic nerve

A

transmit electrical impulses from retina to brain
connects to back of eye near macula
visible portion is called optic disc

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20
Q

what is the macula

A

located roughly in centre of retina, temporal to optic nerve

small and highly sensitive part of retina responsible for detailed central vision

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21
Q

what is the fovea

A

centre of macula

macula allows us to appreciate detail and perform tasks that require central vision e.g reading

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22
Q

why is fovea most sensitive part of retina

A

has highest concentration of cones, but low conc of rods

- only fovea has conc of cones to perceive in detail

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23
Q

what is central vision

A

detail day vision and colour vision

reading, facial recognition

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24
Q

how is central vision assessed

A

by visual acuity assessment

loss of foveal vision = poor visual acuity

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25
Q

how is peripheral vision assessed

A

visual field assessment
extensive loss of visual field = unable to navigate in environment
- patient may need white stick even with perfect visual acuity

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26
Q

what is peripheral vision

A

shape, movement and night vision

and navigation vision

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27
Q

describe retinal structure

A

outer layer = photoreceptors(1st order neurons), detection of light
middle layer = bipolar cells (2nd order), local signal processing to improve contrast sensitivity, regulate sensitivity
inner layer = retinal ganglion cells (3rd order)
transmission of signal to brain

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28
Q

what are the 2 types of photoreceptors

A

rods and cones

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29
Q

what are rods

A 
photoreceptors with longer outer segment with photo-sensitive pigment
100x more sensitive to light than cones
slow response to light
responsible for night vision
are 120 mill rods
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30
Q

what are cones

A

photoreceptors that are less sensitive to light - but have faster response
responsible for daylight, fine vision and colour vision
6 mill cones

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31
Q

what is rod/scotopic vision

A

peripheral and night vision

  • more photoreceptors, more pigment, higher spatial and temporal(time) summation
  • recognises motion
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32
Q

what is cone/photopic vision

A

central and day vision

recognises colour and detail

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33
Q

where can you find highest conc of rod receptors in retina

A

20-40 degrees away from fovea

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34
Q

what are the different receptors that capture different colours

A

s cones - blue
m cones - green
l cones - red

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35
Q

what is deuteranomaly/ daltonism

A

most frequent form of colour blindness

- dont perceive colur red

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36
Q

what is full colour blindness called

A

achromatopsia

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37
Q

what is refraction

A

light travelling from one medium to another,

  • velocity changes
  • path changes
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38
Q

what is the equation for index of refraction

A

speed of light in a vacuum/ speed of light in a medium

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39
Q

what exactly is light doing when reaching new medium

A

some light reflects off boundary and some light refracts through boundary

  1. angle of incidence = angle of reflection
  2. angle of incidence > angle of refraction depending on direction of light
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40
Q

what is a converging/convex lens

A

takes light rays and brings them to a point

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41
Q

what is a diverging/concave lens

A

takes light rays and spreads them outwards

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42
Q

what is emmetropia

A

adequate correlation between axial length and refractive power
parallel light rays fall on retina
- no accommodation

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43
Q

what is ametropia

A

mismatch between axial length and refractive power

parallel light rays dont fall on retina

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44
Q

what is myopia

nearsightedness

A

parallel rays converge at focal point anterior to retina
etiology - not clear, genetic factor?
causes:
1. axial myopia = excessive long globe(more common)
2. refractive myopia = excessive refractive power

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45
Q

what are the symptoms of myopia

A

blurred distance vision
squint to improve uncorrected visual acuity when gazing into distance
headache

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46
Q

treatment for myopia

A

correction with diverging lens
correction with contact lens
correction with removal of lens to reduce refractive power of eye

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47
Q

what is hyperopia

A

parallel rays converge at focal point posterior to retina

etiology - not clear, inherited

48
Q

what are the causes of hyperopia

A
  1. axial hyperopia = excessive short globe, more common

2. refractive hyperopia = insufficient refractive power

49
Q

what are the symptoms of hyperopia

farsightedness

A

symptoms - visual acuity at near ends tend to blur relatively early
- could be inability to read fine print or vision is clear then intermittently blurry

50
Q

when is blurred vision more noticeable

A

if person is tired,

printing is weak or inadequate light

51
Q

what are some asthenopic symptoms

A

eyepain
headache in frontal region
burning sensation in eye
blepharoconjunctivitis

52
Q

what is blepharitis

A

inflammtion along edges of eyelid

53
Q

what is amblyopia

A

uncorrected hyperopia

>5d

54
Q

what is treatment for hyperopia

A

correction with converging/positive lens
correction with positive lens and cataract extraction
correction with contact lens
correction with intraocular lens

55
Q

what is astigmatism

A

parallel rays come to focus in 2 focal lines rather than a single focal point

56
Q

what is the etiology for astigmatism

A

hereditary

57
Q

what are the causes of astigmatism

A

refractive media is not spherical

  • refract differently along one meridian than along meridian perpendicular to it
  • 2 focal points
58
Q

what are the symptoms of astigmatism

A

asthenopic symptoms - headache, eyepain
blurred vision
distortion of vision
head tilting and turning

59
Q

what is the treatment for regular astigmatism

A

cylinder lenses with or without spherical lenses

surgery

60
Q

what is the treatment for irregular astigmatism

A

rigid cylinder lenses

surgery

61
Q

what is the near response triad

A

pupillary miosis (sphincter pupillae) to increase depth of field
convergence (medial recti from both eyes) to align both eyes towards near object
accommodation (circular ciliary muscle) to increase refractive power of lens for near vision

62
Q

what is presbyopia

A

naturally occurring loss of accommodation
onset from 40 yrs age
distant vision intact
corrected by reading glasses

63
Q

what is accommodation

A

focus for near objects

64
Q

what is the treatment for presbyopia

A

convex lenses in near vision

  • reading glasses
  • bifocal glasses
  • trifocal glasses
  • progressive power glasses
65
Q

what spectacle lenses are used for presbyopia correction

A

monofocal lenses, spherical lenses, cylindrical lenses

multifocal lenses

66
Q

what are the advantages of spectacle lenses over contact lenses

A

higher quality of optical image and less influence on size of retinal image than spectacle lenses

67
Q

what are the indications for contact lens use

A 
cosmetic
athletic activities
occupational
irregular corneal astigmatism
high anisometropia
corneal disease
68
Q

what are the disadv of contact lenses

A

careful daily cleaning and disinfection

expensive

69
Q

what are the complications of contact lens use

A

infectious keratitis
giant papillary conjunctivitis
corneal vascularisation
severe chronic conjunctivitis

70
Q

what is apakia

A

not having lens in your eye

71
Q

what are intraocular lenses

A

replacement for cataract crystalline lens

gives best optical correction for aphakia, avoid significant magnification and distortion caused by spectacle lenses

72
Q

what are some examples of keratorefractive surgery

A

rk, ak, prk, lasik, icr, thermokeratoplasty

73
Q

what are some examples of intraocular surgery

A

clear lens extraction ( with/without iol)

phakic iol

74
Q

describe surgical correction of lens

A 
inital cutting of corneal flap
flipping of corneal flap
photorefractive treatment - laser
corneal stroma reshaped post laser
corneal flap back in position
75
Q

what is an icl

A

Staar intra-collamer lens inserted into eye for correction of myopia and astigmatism

76
Q

what is the visual pathway in retina

A

1st order neurones - rod and cone retinal photoreceptors
2nd order neurones - retinal bipolar cells
3rd order neurones - retinal ganglion cells
- opitic nerve
- partial decussation at optic chiasm(53% of ganglion fibres cross midline)
optic tract
destination = lateral geniculate nucleus in thalamus - to relay visual info to visual cortex

77
Q

describe optic chiasma

A

lesions anterior to chiasm affect visual field in one eye only
lesions posterior to chiasm afects visual field in both eyes

78
Q

where do the crossed fibres in visual pathway originate from

A

nasal retina, responsible for temporal visual field

79
Q

what do uncrossed fibres in visual pathway originate from

A

from temporal field and are responsible for nasal visual field

80
Q

what can lesions at optic chiasm cause

A

damages crossed ganglion fibres from nasal retina in both eyes
temporal field deficit in both eyes - bitemporal heia..

81
Q

what is bitemporal hemianopia typically caused by

A

enlargement of pituitary gland tumour

82
Q

what is homonymous hemianopia typically caused by

A

stroke - cerebrovascular accident

area representing macula receives dual blood supply from posterior cerebral arteries from both sides

83
Q

why do pupils constrict in light

A

decreases spherical aberrations and glare
increases depth of fiels
reduces bleaching of photopigments
pupillary constriction mediated by parasympathetic nerve

84
Q

why do pupils dilate in dark

A

increases light sensitivity in dark by allowing more light into eye
pupillary dilation mediated by sympathetic nerve

85
Q

what is the afferent pathway for pupillary reflex

A

rod and cone receptors synapsing on bipolar cells synapse on retinal ganglion cells
pupil specific ganglion cells exit at posterior third of optic tract before entering lateral geniculate nucleus
afferent pathway from each eye synapses on edinger-westpal nuclei on both sides in brainstem

86
Q

what is the efferent pathway for pupillary reflex

A

edinger-westpal nucleus -> oculomotor nerve efferent -> synapses at ciliary ganglion -> short posterior ciliary nerve -> pupillary sphincter

87
Q

what is the consensual light reflex

A

constriction of pupil of other eye

88
Q

what is the neurological basis of consensual light reflex

A

afferent pathway on either side alone stimulates efferents on both sides

89
Q

what would you see with right afferent defect in pupillary reflex
e.g damage to optic nerve

A

pupil constriction in both eyes when right eye is stimulated with light
normal constriction when left eye stimulated with light

90
Q

what would you expect to see with right efferent damage in pupillary reflex
e.g damage to right 3rd nerve

A

no right pupil constriction with left or right eye stimulated with light
left pupil constricts whether right / left is stimulated with light

91
Q

what would you expect to see with unilateral afferent defect in pupillary reflex

A

different response depending on which eye stimulated

92
Q

what would you expect to see with unilateral efferent defect in pupillary reflex

A

same unequal response between left and right eye irrespective of which eye stimulated

93
Q

what is the relative afferent pupillary defect

A

partial pupillary response is still present when damaged eye is stimulated

  • both pupils constrict when light swings to left undamaged side
  • both pupils paradoxically dilate when light swings to right damaged side
94
Q

what are eye movements facilitated by

A

six extraocular muscles innervated by 3 cranial nerves - 3,4 and 6

95
Q

what is duction

A

eye movement in one eye

96
Q

what is version

A

simultaneous movement of both eyes in opposite direction

97
Q

what is vergence

A

simultaneous movement of both eyes in opposite direction

98
Q

what is convergence

A

simultaneous adduction movement in both eyes when viewing near object

99
Q

what is saccade

A

short fast burst upto 900’/sec

100
Q

what are some examples of saccade

A

reflexive saccade to external stimuli
scanning saccade
predictive saccade to track objects
memory guided saccade

101
Q

what is smooth pursuit in context of speed of eye movement

A

sustain slow movement
upto 60’/s
driven by motion of moving target across retina

102
Q

what are the 6 extraocular muscles

A 
superior rectus
inferior rectus
lateral rectus
medial rectus
superior oblique
inferior oblique
103
Q

what is the superior rectus

A

attached to eye at 12 oclock

moves eye up

104
Q

what is the inferior rectus

A

attached to eye at 6 oclock

moves eye down

105
Q

what is the lateral rectus

A

also called external rectus
attaches on temporal side of eye
moves eye towards outside of head

106
Q

what is the medial rectus

A

aka internal rectus
attached on nasal side of eye
moves eye towards middle of head

107
Q

what is the superior oblique

A

attached on temporal side of eye
passes under superior rectus
moves eye down and out diagonally
travels through the trochlea

108
Q

what is the inferior oblique

A

attached low on nasal side of eye
passes over inferior rectus
moves eye up and out in diagonal pattern

109
Q

what is role of 3rd cranial nerve - oculomotor nerve in eye

A 
1. superior branch:
superior rectus - elevates eye
levator palpebrae superiosis - raises eyelid
2. inferior branch:
inferior rectus - depresses eye
medial rectus - adducts eye
inferior oblique - elevates eye
parasympathetic nerve - constricts pupil
110
Q

which cranial nerve is responsible for depressing eye via superior oblique

A

4th cranial nerve - trochlear

111
Q

what nerve os responsible for abducting eye via lateral rectus

A

6th - abducens

112
Q

what is 3rd nerve palsy

A

affected eye moves down and out
droopy eyelids - loss of elevator palpebrae superiosis
unopposed superior oblique innervated by 4th nerve,down
unopposed lateral rectus action innervated by 6th nerve, down

113
Q

what is 6th nerve palsy

A

affected eye unable to abduct and deviate inwards

double vision worsens on gazing to side of affected eye

114
Q

what is nystagmus

A

oscillating eye movement

115
Q

what is optokinetic nystagmus

A

smooth pursuit and fast phase reset saccade

116
Q

what is optokinetic nystagmus reflex

A

useful in testing visual acuity in preverbal children by observing presence of nystagmus movement in response to moving grating patterns of various spatial frequencies

117
Q

what does presence of optokinetic nystagmus in response to moving grating signify

A

subject has sufficient visual acuity to perceive grating pattern

brs2 (65 decks)

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