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Semester 3: Mind and Movement > PBL Topic 3 Case 3 > Flashcards

PBL Topic 3 Case 3 Flashcards

1
Q

What occurs when a light ray travelling in a beam strikes an interface that is perpendicular to the beam?

A
  • Same course
  • Decrease in velocity
  • Shorter wavelength
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2
Q

What occurs when a light ray travelling in a beam strikes an angulated surface?

A
  • Refraction

- Light rays bend

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3
Q

What happens when parallel light rays enter a convex lens?

A
  • Convergence of rays at the focal point
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4
Q

What happens when parallel light rays enter a concave lens?

A
  • Divergence of rays
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5
Q

Identify the four refractive interfaces in the lens system of the eye.

A
  • Air and anterior surface of cornea
  • Posterior surface of cornea and aqueous humor
  • Aqueous humor and anterior surface of lens
  • Posterior surface and vitreous humor
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6
Q

What is meant by the term diopter?

A
  • A unit of refractive power

- Which is reciprocal to the focal length of a given lens

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7
Q

What is the total refractive power of the eye?

A
  • 59 diopters
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8
Q

What is the accommodation reflex?

A
  • Voluntary increase in refractive power
  • To focus on a nearby object,
  • The eyes converge, the lens becomes more convex and the pupils constrict
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9
Q

Outline the mechanism of accommodation

A
  • Efferent impulses pass in the oculomotor nerve to the orbit
  • There they synapse in the ciliary ganglion which give rise to small ciliary nerves
  • These nerves stimulate contraction of ciliary muscle, which relaxes ligaments of the lens
  • Which enables the lens to assume a more convex shape.
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10
Q

What is presbyopia?

A
  • With age the lens grows larger and thicker and less elastic
  • The ability of the lens to change shape decreases, and the accommodation reflex decreases
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11
Q

What is am emmetropic eye?

A
  • Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed
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12
Q

What is hyperopia?

A
  • Farsightedness due to a short eyeball
  • Parallel light rays are not bent sufficiently by the relaxed lens system to come to focus
  • So ciliary must contract to increase the strength of the lens
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13
Q

What is myopia?

A
  • Shortsightedness due to a long eyeball
  • Parallel light rays from distant objects are not focused in front of the retina when the ciliary muscle is completely replaced
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14
Q

What is astigmatism?

A
  • Refractive error in which curvature of the cornea in one plane of the eye is too great
  • Such that light rays do not come to a focal point.
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15
Q

Why can the accommodation power of the eye not compensate for astigmatism?

A
  • The curvature of the lens changes approximately equally in both planes
  • Each of the two planes requires a different degree of accommodation which is not possible
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16
Q

What is visual acuity?

A
  • The ability of the eye to discriminate between two points of light
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17
Q

What is the purpose of intraocular fluid?

A
  • To maintain sufficient pressure in the eyeball to keep is distended
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18
Q

Where is intraocular fluid located?

A
  • Aqueous humor, located in front of the eyes

- Vitreous humor, located between posterior surface of the lens and retina.

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19
Q

Outline how aqueous humor is formed and reabsorbed

A
  • It is secreted by the epithelia of the ciliary processes
  • Diffuses of sodium and chloride ions into the spaces between epithelial cells
  • Which causes osmosis of water into the same area
  • Flows through the pupil into the anterior chamber of the eye, lens, corona and iris
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20
Q

Outline how aqueous humor is reabsorbed?

A
  • Passes through trabeculae before emptying into the canal of Schlemm
  • Which empties into the extra ocular veins
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21
Q

What is the average intraocular pressure?

A
  • 15 mmHg
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22
Q

How can intraocular pressure be measured?

A
  • Tonometry
  • Small force is applied to a plunger
  • Causing cornea to be displaced inward
  • Degree of displacement is calibrated in terms of intraocular pressure
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23
Q

Outline the pathology of glaucoma?

A
  • Intraocular pressure rises above 60 mmHg
  • Which puts pressure on the axons of the optic nerve
  • Resulting in lack of nutrition of the fibres, resulting in death of the fibres
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24
Q

Identify three treatments of glaucoma?

A
  • Drugs that reduce secretion of intraocular fluid
  • Drugs that increase absorption of intraocular fluid
  • Surgical procedure include increasing spaces of trabeculae
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25
Q

What is the retina?

A
  • Light-sensitive portion of the eye

- Which contains photoreceptors (e.g. rods and cones)

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26
Q

Identify the eight layers of the retina

A
  • Pigmented layer (vitamin A and melanin)
  • Layer of rods and cones
  • Outer nuclear layer (cell bodies of rods and cones)
  • Outer plexiform layer (horizontal cells)
  • Inner nuclear layer (bipolar cells)
  • Inner plexiform layer (amacrine cells)
  • Ganglionic layer
  • Layer of optic nerve fibres
  • Inner limiting membrane
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27
Q

What is the role of melanin?

A
  • Melanin, which prevents light reflection throughout the globe of the eyeball
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28
Q

What is the fovea?

A
  • The small area in the centre of the retina

- Composed of long thin cones

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29
Q

Describe the structure of the photoreceptors

A
  • Outer segment is composed of photochemicals (either rhodopsin or colour pigment)
  • Discs, which are unfolded shelves of cell membrane
  • Inner segment containing cytoplasm and cytoplasmic organelles e.g. mitochondria
  • Synaptic body that connects to horizontal and bipolar cells
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30
Q

Identify the two components of rhodpsin

A
  • Scotopsin

- 11-cis retinal

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31
Q

Identify the pathway in which rhodopsin is activated

A
  • Light energy is absorbed by rhodopsin
  • 11-cis retinal is converted to 11-trans retinal
  • 11-trans retinal is unable to bind with 11-cis retinal
  • So rhodopsin decomposes into a number of intermediate products e.g. bathorhodopsin, lumirhodopsin, metarhodopsin I
  • And finally to metarhodopsin II (activated rhodopsin)
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32
Q

Identify two ways in which rhodopsin is reformed

[A] From 11-trans retinal

[B] From vitamin A

A
  • [A] 11-trans retinal is converted to 11-cis retinal by retinal isomerase
  • [B] 11-trans retinal is converted to Vitamin A, which is then converted to 11-cis retinol, which is converted to 11-cis retinal by retinal isomerase
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33
Q

Why does night blindness occur in people with vitamin A deficiency?

A
  • Less 11-cis retinal formed from Vitamin A
  • So less rhodopsin is formed (light-sensitive chemical)
  • So light-sensitivity in the dark is reduced
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34
Q

Which enzyme inactivates metarhodopsin II?

A
  • Rhodopsin kinase
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35
Q

Identify the two components of the cone photochemicals?

A
  • Photopsin

- Retinal

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36
Q

Name the three colour pigments present in each cone.

A
  • Blue
  • Green
  • Red
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37
Q

How is the nervous system able to interpret different colours other than blue red and green?

A
  • Red, green and blue cones are stimulated in different ratios depending on the colour
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38
Q

What is meant by the term protanope?

A
  • A person with loss of red cones
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39
Q

What is meant by the term deuteranope?

A
  • A person with loss of green cones
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40
Q

What is light adaptation?

A
  • When light energy is absorbed, the light-sensitive chemical rhodopsin is reduced to scotopsin and 11-trans retinal
  • So sensitivity to light is reduced
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41
Q

What is dark adaptation?

A
  • When there is less light energy acting on rods, 11-cis retinol is able to bind with scotopsin to form rhodopsin, a light-sensitive chemical
  • So sensitivity to light is increased
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42
Q

Identify two other mechanisms for light and dark adaptation that do not involve rods or cones

A
  • Change in pupillary size, reducing the amount of light through the pupillary opening
  • Neural adaptation in which signals transmitted by bipolar, horizontal, amacrine and ganglion cells are intense when light intensity increases
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43
Q

Horizontal cells:

  • In which layer are they located?
  • What do they transmit?
  • What type of signals do they transmit?
A
  • Located in outer plexiform layer
  • Which transmit signals from photoreceptors to bipolar cells
  • Inhibitory signals
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44
Q

Bipolar cells:

  • In which layer are they located?
  • What do they transmit?
  • What type of signals do they transmit?
A
  • Between outer plexiform and inner plexiform layer
  • Which transmit signals from rods, cones and horizontal cells to ganglion and amacrine cells
  • Both excitatory and inhibitory signals
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45
Q

Amacrine cells:

  • In which layer are they located?
  • What do they transmit?
A
  • Inner plexiform layer

- Which transmit signals from bipolar cells to ganglion cells

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46
Q

Ganglion cells:

  • In which layer are they located?
  • What do they transmit?
A
  • Ganglion cell layer

- Which transmit output signals from retina through the optic nerve to the brain

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47
Q

Identify the three type of ganglion cells

A
  • W cells which transmit rod vision
  • X cells which transmit visual image and colour
  • Y cells which transmit instantaneous changes in the visual image
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48
Q

Identify the neurotransmitters involved at each synapse in the retina

A
  • Photoreceptors release glutamate
  • Amacrine cells release GABa, glycine, ACh and dopamine
  • Bipolar and horizontal cells, unclear, but inhibitory neurotransmitters
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49
Q

In which retinal cell type are signals transmitted by means of action potential?

A
  • Ganglionic cells
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50
Q

What is the importance of electrical conduction in all other cell types?

A
  • Allows for graded conduction
  • Meaning the strength of hyperpolarisation output signals is directly related to intensity of illumination
  • It is NOT an all or one principle like an action potential
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51
Q

Why is electrical conduction not used in the ganglion cells?

A
  • Due to long distance
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52
Q

How are colour signals transmitted by ganglion cells?

A
  • One colour type while excite a specific ganglion cell by the direct excitatory route through a depolarising bipolar cell
  • While another will inhibit it by the indirect inhibitory route through a hyperpolarising bipolar cell
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53
Q

Outline the pathway taken by optic nerve fibres at the optic chiasm?

A
  • Nerve fibres from the nasal halves cross to the opposite side where they join temporal fibres of the opposite retina
  • To form the optic tract
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54
Q

Outline the nerve pathway from the optic tract to the primary visual cortex

A
  • Synapse in dorsal lateral geniculate nucleus of the thalamus
  • Geniculocalcarine fibres pass through geniculocalcarine tract to the primary visual cortex
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55
Q

What is the role of those nerve fibres that pass to the suprachiasmatic nucleus of the hypothalamus?

A
  • Control circadian rhythms that synchronise changes of the body with night and day
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56
Q

What is the role of those nerve fibres that pass to the pretectal nuclei of the midbrain?

A
  • Pupillary light reflex
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57
Q

What is the role of those nerve fibres that pass to the superior colliculus of the midbrain?

A
  • Control rapid directional movements of the eyes
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58
Q

What is the role of those nerve fibres that pass to ventral lateral geniculate nucleus of the thalamus?

A
  • Control some of the body’s behavioural functions
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59
Q

Identify the different layers of the dorsal lateral geniculate nucleus and their respective roles.

A
  • Layers 2,3 and 5 receive signals from the lateral half of the ipsilateral retina
  • Layers 1,4 and 6 receive signals from the medial half of the opposite eye.
60
Q

Outline the ‘gate’ function of the dorsal lateral geniculate nucleus

A
  • DLGN receives corticofugal fibres returning from primary visual cortex and from reticular areas of mesencephalon
  • These are inhibitory signals that can turn off transmission through the DLGN
61
Q

What are the magnocellular layers of the DLGN?

A
  • Layers 1 and 2

- Receiving input from Y cells (instantaneous changes in visual image)

62
Q

What are the parvocellular layers of the DLGN?

A
  • Layers 3, 4, 5 and 6

- Receiving input from X cells (visual image and colour)

63
Q

Where is the primary visual cortex located?

A
  • Calcarine fissure

- Extending from occipital pole on the medial aspect of each occipital cortex

64
Q

Where are the secondary visual areas located and what is their role?

A
  • Anterior, lateral, superior and inferior to the primary visual cortex
  • Responsible for analysis of visual meanings
65
Q

How many layers are there in the primary visual cortex?

A
  • 6
66
Q

In which layer do geniculocalcarine fibres terminate?

A
  • 4
67
Q

In which layer do rapidly conducted signals from Y-cells terminate?

A
  • 4c alpha
68
Q

In which layer do signals from X- cells terminate?

A
  • 4a

- 4c beta

69
Q

Identify the two fields of vision

A
  • Nasal field seen to the nasal side

- Temporal field seen to the temporal side

70
Q

How is visual field assessed?

A
  • Perimetry
  • Patient closes one eye while looking at a central spot with the other eye
  • Central spot moves and the patient indicates when they can / cannot see the spot
71
Q

Where is the blind spot?

A
  • 15 degrees lateral to the central point of vision
72
Q

What causes the blind spot?

A
  • Lack of rods and cones over the optic disc
73
Q

What is scotoma?

A
  • Blind spots in other portions of the visual field other than over the optic disc
  • Caused by damage to the optic nerve e.g. gluacoma
74
Q

Identify the three pairs of muscles responsible for eye movements

A
  • Medial and lateral recti, which move the eyes from side to side
  • Superior and inferior recti, which move the eyes up and down
  • Superior and inferior obliques which contract to rotate the eyeballs to keep the visual fields in the upright position
75
Q

What is meant by reciprocal innervation?

A
  • Muscles of a pair are innervated such that one muscle contracts when the other relaxes
76
Q

What is the voluntary fixation mechanism?

Where in the brain is this mechanism controlled from?

A
  • Allows person to moves eyes voluntarily to find the object to fixate on
  • Premotor cortical areas of the frontal lobes
77
Q

What is the involuntary fixation mechanism?

Where in the brain is this mechanism controlled from?

A
  • Holds eyes firmly on the object once it has been found

- Secondary visual areas in the occipital lobe

78
Q

What is meant by opticokinetic movement?

A
  • Persons eyes jump from one point to the next (saccades)
79
Q

What is meant by pursuit movement?

A
  • Persons eyes fixate on a moving object
80
Q

What neuronal mechanisms are involved in the turning of the head towards a sudden visual disturbance?

A
  • Superior colliculus sends oculomotor signals to brain stem nuclei of oculomotor nerves
81
Q

What is stereopsis?

A
  • The perception of depth produced by the reception in the brain of visual stimuli from both eyes in combination
82
Q

What is strabismus?

A
  • Lack of fusion of the eyes in one or more visual coordinates
83
Q

Identify three types of stabismus

A
  • Horizontal
  • Torsional
  • Vertical strabismus?
84
Q

What is the cause of strabismus?

A
  • Abnormal set of the fusion mechanism of the visual system
  • One eye is able to fixate successfully
  • The other eye is unsuccessful and the eye becomes abnormally set in another neuronal control pathway
85
Q

What is a cataract?

A
  • Error in refraction
  • Cloudy opaque area in the lens caused by denaturation of proteins within the lens that coagulate
  • Most common cause of preventable blindness in the world
86
Q

Identify three metabolic causes of cataracts

A
  • Diabetes
  • Hypocalcaemia
  • Wilson’s disease
87
Q

Identify an inflammatory cause of cataracts

A
  • Uveitis
88
Q

Identify the treatment of a cataract

A
  • Small incision extracapsular or phacoemulsificaiton extraction
  • With insertion of intraocular lens
89
Q

Identify three risk factors of primary open angle glaucoma

A
  • Age
  • Race (Black African)
  • Positive family history
  • Myopia
90
Q

Why is timolol used in the treatment of primary open angle glaucoma?

A
  • Reduces aqueous production
91
Q

Why is latanoprost used in the treatment of primary open angle glaucoma?

A
  • Increases aqueous drainage
92
Q

Why are carbonic anhydrase inhibitors such as acetazolamide used in the treatment of primary open angle glaucoma?

A
  • Slows the formation of bicarbonate

- Reduces sodium and fluid transport

93
Q

How do the clinical features of primary open angle glaucoma differ from those of acute angle-closure glaucoma?

A
  • POAG: Gradual, painless loss of peripheral visual field

- AACG: Red painful eye, blurred vision, nausea, vomiting, severe ocular pain

94
Q

Why is pilocarpine used in the treatment of acute angle-closure glaucoma?

A
  • Constricts pupil to improve aqueous outflow

- Prevents iris adhesion to trabecular meshwork

95
Q

What is trabeculectomy?

A
  • Making a hole in the periphery of the iris increasing spaces of trabeculae
96
Q

Outline the pathology of retinal detachment

A
  • Tear in retina

- Fluid collects in potential space between sensory retina and pigment epithelium

97
Q

What are the clinical features of retinal detachment?

A
  • Visual field loss
  • Floaters
  • Flashes of light (photopsia)
98
Q

What is the treatment of retinal detachment?

A
  • Laser surgery to scar edge of retinal tear

- Thereby attaching the retina back to the eye

99
Q

Outline the pathology of retinal pigmentosa

A
  • Common chronic inherited degenerative disease. Several genes are implicated.
  • Constriction of the peripheral vision leading to tunnel vision and progressive loss of night vision.
  • Spicule deposits and attenuated retinal vessels.
    .
100
Q

What is the treatment of retinal pigmentosa?

A
  • Vitamin A supplementation may slow progression

- Gene therapy is being investigated

101
Q

Identify risk factors in age related macular degeneration

A
  • Smoking
  • Hypertension
  • Hypercholesterolaemia
  • UV exposure
102
Q

Identify two types of AMD

A
  • Non-exudative (dry) with lipofuscin deposits

- Exudative (wet) AMD with subfoveal choroidal neovascularisation

103
Q

What is the treatment of AMD?

A
  • Vitamins C, E, beta carotene, zinc copper

- Intravitreal injections of anti-vascular endothelial growth factor such as ranibzumab

104
Q

How are visual fields assessed at bedside?

A
  • Confrontation

- Comparing the examiner’s eye and patient’s fields, one eye at a time, quadrant by quadrant

105
Q

Identify two detailed tests of visual fields?

A
  • Goldmann (manual) perimetry testing

- Humphrey (automated) perimetry testing

106
Q

What is meant by hemianopia?

A
  • When half of visual field is affected
107
Q

What is meant by quandrantanopia?

A
  • When a quadrant of a visual field is affected
108
Q

Lesions of which region produce homonymous field defects?

A
  • Lesions posterior to the optic chiasm
  • Indicating involvement of the same part of the visual field in both eyes
  • As information from the two visual fields is separated beyond this point
109
Q

Lesions damaging which fibres cause bitemporal defects?

A
  • Lesions damaging the decussating nasal fibres at the optic chiasm
110
Q

Mononuclear field loss is caused by a nerve lesion located at [A] and may be due to [B]

A
  • [A] Optic nerve

- [B] Optic neuritis

111
Q

BItemporal hemianopia is caused by a lesion located at [A] and may be due to [B]

A
  • [A] Optic chiasm

- [B] Pituitary tumours

112
Q

Incongruous contralateral homonymous hemianopia is caused by a lesion located at [A] and may be due to [B]

A
  • [A] Optic tract
  • [B] Tumour, stroke
    or inflammatory disease
113
Q

What type of visual field loss occurs in damage to

[A] Temporal lobe

[B] Parietal lobe

A
  • [A] Contralateral homonymous upper quadrantanopia

- [B] Contralateral homonymous lower quadrantanopia

114
Q

What is meant by macular sparing and why can damage to the occipital lobe be macular sparing?

A
  • Signals from the macula terminate at the occipital pole,
  • Therefore a lesion located anterior to the optic pole can produce macula sparing
  • Which means that the centre of vision is spared
115
Q

Outline process of phototransduction

A
  • Breakdown of rhodopsin to activated metarhodopsin
  • Which activated transducin
  • Which activates cGMP-phosphodiesterase
  • Which breaks down cGMP
  • Closure of cationic channels
  • Hyperpolarisation which excites cell
116
Q

What is the effect of phenylephrine on pupillary diameter?

A
  • Mydriasis (dilation)

- Since it is an alpha-1 agonist

117
Q

What is the effect of tropicamide on pupillary diameter?

A
  • Mydriasis (dilation)

- Since it is an M3 antagonist

118
Q

What is the effect of pilocarpine on pupillary diameter?

A
  • Miosis (constriction)

- Since it is an M3 agonist

119
Q

What is miosis?

A
  • Pupillary constriction
120
Q

Outline the mechanism behind miosis

A
  • Light stimulus excites photoreceptors
  • Signal sent via the optic nerve and optic tract to the pretectal nucleus
  • Signal is relayed to the Edinger Westphal nucleus
  • Efferent impulses pass along parasympathetic fibres of oculomotor nerve
  • Synapse in ciliary ganglion
  • Short ciliary nerves pass to sphincter pupillae
  • Which constricts the pupil
121
Q

What is mydriasis?

A
  • Pupillary dilation
122
Q

Outline the mechanism behind mydriasis

A
  • Fibres arise from T1 and T2
  • Impulses pass via sympathetic trunk to superior cervical ganglion
  • Long ciliary nerves pass to dilator pupillae
  • Which dilates the pupil
123
Q

What is the cause of Horner’s syndrome?

A
  • Interruption to sympathetic nerves in the cervical sympathetic chain
  • E.g. tumour
124
Q

Outline 3 clinical features of Horner’s syndrome

A
  • Ptosis
  • Miosis
  • Anhydrosis
125
Q

How is a myopic eye corrected?

A
  • Concave lens
  • Which diverges light rays
  • Enhanced focus of the image on the retina
126
Q

How is a hyperopic eye corrected?

A
  • Convex lens
  • Which converges light rays
  • Enhanced focus of the image on the retina
127
Q

Identify the two components of the pupillary light reflex

A
  • Direct component mediates constriction of the ipsilateral pupil
  • Consensual component mediates constriction of the contralateral pupil
128
Q

What is amblyopia?

A
  • Reduction in visual acuity
  • Due to disruption of the visual image of one eye but not the other in early development
  • Causing failure of development of the visual system
129
Q

At what age does amblyopia develop and before which age must it be detected and treated to prevent blindness?

A
  • Age 2

- Age 8

130
Q

Why can strabismus cause amblyopia?

A
  • Misalignment of each eye results in different retinal images being sent to the visual cortex
131
Q

Why does amblyopia not occur in adults? What occurs in adults when a visual image is suppressed?

A
  • The visual cortex pathway are developed

- Diplopia

132
Q

Which of Brodmann’s area are the secondary visual areas located?

A
  • 18 and 19
133
Q

Where is the ‘What?’ Pathway located and what is it concerned with?

A
  • Medially in association area
  • Colour medially
  • Faces in the middle region
  • Form laterally
134
Q

Where is the ‘Where?’ Pathway located and what is it concerned with?

A
  • Laterally in association area

- Movement in contralateral visual hemifield

135
Q

What is felt stigma?

A
  • A change in self identity that is manifested as shame, guilt and withdrawal
136
Q

What is enacted stigma?

A
  • Societal reactions that cause actual discriminatory experiences either:
  • Directly, treated less favourable
  • Indirectly, particularly groups are likely to suffer effects of rules, systems, procedures
137
Q

Outline the negative feedback circle of stigma

A
  • Disability causes restriction of activities and social roles
  • Which causes negative labelling
  • Which causes diminished self-esteem and ‘felt stigma’
  • Resulting in isolation and withdrawal from social life
  • Resulting in lack of confidence and skills
  • Which causes further restriction of activities and social roles
138
Q

What is a virtuous circle in relation to stigma

A
  • Positive challenges to stigma can change attitudes that lead to enacted stigma
  • Which in turn reduce felt stigma
  • Which itself reduces enacted stigma by changing behaviours such as stigmatisation and withdrawal
139
Q

Identify five strategies to tackle stigma

A
  • Legislation
  • Education
  • Language
  • Public acknowledgement
  • Treatment
140
Q

Outline the Medical Model of Disability

A
  • Disability caused by health condition or impairment

- By fixing the body, disabled people can participate in society like everyone else

141
Q

Outline the Social Model of Disability

A
  • Distinguishes between impairment (loss of functioning part of body) and disability (meaning society attaches to impairment)
  • Three barriers include environment, attitudes and organisations
142
Q

What is Activities of Daily Living and how is it measured?

A
  • Assessment of disability
  • How an impairment affects everyday activities
  • Measured as elf-report and observation
143
Q

What is sensation?

A
  • The detection of simple properties of stimuli

- Such as brightness, colour and sweetness

144
Q

What is perception?

A
    • Detection of objects, their locations, movements and backgrounds
145
Q

What is bottom’s up processing?

A
  • Analysis of stimuli into a set of features
  • Which are compared to existing sets in the brain
  • Recognition occurs if a match occurs
146
Q

What is top-down processing?

A
  • Contextual and based on expectancy

- People see what they expect or want to see

147
Q

Define attention

A
  • Directing and focusing of perception

- May be selective, divided or focused and can be negatively affected by stress or fatigue

Semester 3: Mind and Movement (21 decks)

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