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
2
Q
What occurs when a light ray travelling in a beam strikes an angulated surface?
A
- Refraction
- Light rays bend
3
Q
What happens when parallel light rays enter a convex lens?
A
- Convergence of rays at the focal point
4
Q
What happens when parallel light rays enter a concave lens?
A
- Divergence of rays
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
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
7
Q
What is the total refractive power of the eye?
A
- 59 diopters
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
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.
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
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
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
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
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.
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
16
Q
What is visual acuity?
A
- The ability of the eye to discriminate between two points of light
17
Q
What is the purpose of intraocular fluid?
A
- To maintain sufficient pressure in the eyeball to keep is distended
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.
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
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
21
Q
What is the average intraocular pressure?
A
- 15 mmHg
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
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
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
25
What is the retina?
- Light-sensitive portion of the eye
| - Which contains photoreceptors (e.g. rods and cones)
26
Identify the eight layers of the retina
- 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
27
What is the role of melanin?
- Melanin, which prevents light reflection throughout the globe of the eyeball
28
What is the fovea?
- The small area in the centre of the retina
| - Composed of long thin cones
29
Describe the structure of the photoreceptors
- 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
30
Identify the two components of rhodpsin
- Scotopsin
| - 11-cis retinal
31
Identify the pathway in which rhodopsin is activated
- 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)
32
Identify two ways in which rhodopsin is reformed
[A] From 11-trans retinal
[B] From vitamin 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
33
Why does night blindness occur in people with vitamin A deficiency?
- Less 11-cis retinal formed from Vitamin A
- So less rhodopsin is formed (light-sensitive chemical)
- So light-sensitivity in the dark is reduced
34
Which enzyme inactivates metarhodopsin II?
- Rhodopsin kinase
35
Identify the two components of the cone photochemicals?
- Photopsin
| - Retinal
36
Name the three colour pigments present in each cone.
- Blue
- Green
- Red
37
How is the nervous system able to interpret different colours other than blue red and green?
- Red, green and blue cones are stimulated in different ratios depending on the colour
38
What is meant by the term protanope?
- A person with loss of red cones
39
What is meant by the term deuteranope?
- A person with loss of green cones
40
What is light adaptation?
- When light energy is absorbed, the light-sensitive chemical rhodopsin is reduced to scotopsin and 11-trans retinal
- So sensitivity to light is reduced
41
What is dark adaptation?
- 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
42
Identify two other mechanisms for light and dark adaptation that do not involve rods or cones
- 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
43
Horizontal cells:
- In which layer are they located?
- What do they transmit?
- What type of signals do they transmit?
- Located in outer plexiform layer
- Which transmit signals from photoreceptors to bipolar cells
- Inhibitory signals
44
Bipolar cells:
- In which layer are they located?
- What do they transmit?
- What type of signals do they transmit?
- 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
45
Amacrine cells:
- In which layer are they located?
- What do they transmit?
- Inner plexiform layer
| - Which transmit signals from bipolar cells to ganglion cells
46
Ganglion cells:
- In which layer are they located?
- What do they transmit?
- Ganglion cell layer
| - Which transmit output signals from retina through the optic nerve to the brain
47
Identify the three type of ganglion cells
- W cells which transmit rod vision
- X cells which transmit visual image and colour
- Y cells which transmit instantaneous changes in the visual image
48
Identify the neurotransmitters involved at each synapse in the retina
- Photoreceptors release glutamate
- Amacrine cells release GABa, glycine, ACh and dopamine
- Bipolar and horizontal cells, unclear, but inhibitory neurotransmitters
49
In which retinal cell type are signals transmitted by means of action potential?
- Ganglionic cells
50
What is the importance of electrical conduction in all other cell types?
- 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
51
Why is electrical conduction not used in the ganglion cells?
- Due to long distance
52
How are colour signals transmitted by ganglion cells?
- 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
53
Outline the pathway taken by optic nerve fibres at the optic chiasm?
- 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
54
Outline the nerve pathway from the optic tract to the primary visual cortex
- Synapse in dorsal lateral geniculate nucleus of the thalamus
- Geniculocalcarine fibres pass through geniculocalcarine tract to the primary visual cortex
55
What is the role of those nerve fibres that pass to the suprachiasmatic nucleus of the hypothalamus?
- Control circadian rhythms that synchronise changes of the body with night and day
56
What is the role of those nerve fibres that pass to the pretectal nuclei of the midbrain?
- Pupillary light reflex
57
What is the role of those nerve fibres that pass to the superior colliculus of the midbrain?
- Control rapid directional movements of the eyes
58
What is the role of those nerve fibres that pass to ventral lateral geniculate nucleus of the thalamus?
- Control some of the body's behavioural functions
59
Identify the different layers of the dorsal lateral geniculate nucleus and their respective roles.
- 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
Outline the 'gate' function of the dorsal lateral geniculate nucleus
- 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
What are the magnocellular layers of the DLGN?
- Layers 1 and 2
| - Receiving input from Y cells (instantaneous changes in visual image)
62
What are the parvocellular layers of the DLGN?
- Layers 3, 4, 5 and 6
| - Receiving input from X cells (visual image and colour)
63
Where is the primary visual cortex located?
- Calcarine fissure
| - Extending from occipital pole on the medial aspect of each occipital cortex
64
Where are the secondary visual areas located and what is their role?
- Anterior, lateral, superior and inferior to the primary visual cortex
- Responsible for analysis of visual meanings
65
How many layers are there in the primary visual cortex?
- 6
66
In which layer do geniculocalcarine fibres terminate?
- 4
67
In which layer do rapidly conducted signals from Y-cells terminate?
- 4c alpha
68
In which layer do signals from X- cells terminate?
- 4a
| - 4c beta
69
Identify the two fields of vision
- Nasal field seen to the nasal side
| - Temporal field seen to the temporal side
70
How is visual field assessed?
- 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
Where is the blind spot?
- 15 degrees lateral to the central point of vision
72
What causes the blind spot?
- Lack of rods and cones over the optic disc
73
What is scotoma?
- 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
Identify the three pairs of muscles responsible for eye movements
- 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
What is meant by reciprocal innervation?
- Muscles of a pair are innervated such that one muscle contracts when the other relaxes
76
What is the voluntary fixation mechanism?
Where in the brain is this mechanism controlled from?
- Allows person to moves eyes voluntarily to find the object to fixate on
- Premotor cortical areas of the frontal lobes
77
What is the involuntary fixation mechanism?
Where in the brain is this mechanism controlled from?
- Holds eyes firmly on the object once it has been found
| - Secondary visual areas in the occipital lobe
78
What is meant by opticokinetic movement?
- Persons eyes jump from one point to the next (saccades)
79
What is meant by pursuit movement?
- Persons eyes fixate on a moving object
80
What neuronal mechanisms are involved in the turning of the head towards a sudden visual disturbance?
- Superior colliculus sends oculomotor signals to brain stem nuclei of oculomotor nerves
81
What is stereopsis?
- The perception of depth produced by the reception in the brain of visual stimuli from both eyes in combination
82
What is strabismus?
- Lack of fusion of the eyes in one or more visual coordinates
83
Identify three types of stabismus
- Horizontal
- Torsional
- Vertical strabismus?
84
What is the cause of strabismus?
- 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
What is a cataract?
- 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
Identify three metabolic causes of cataracts
- Diabetes
- Hypocalcaemia
- Wilson's disease
87
Identify an inflammatory cause of cataracts
- Uveitis
88
Identify the treatment of a cataract
- Small incision extracapsular or phacoemulsificaiton extraction
- With insertion of intraocular lens
89
Identify three risk factors of primary open angle glaucoma
- Age
- Race (Black African)
- Positive family history
- Myopia
90
Why is timolol used in the treatment of primary open angle glaucoma?
- Reduces aqueous production
91
Why is latanoprost used in the treatment of primary open angle glaucoma?
- Increases aqueous drainage
92
Why are carbonic anhydrase inhibitors such as acetazolamide used in the treatment of primary open angle glaucoma?
- Slows the formation of bicarbonate
| - Reduces sodium and fluid transport
93
How do the clinical features of primary open angle glaucoma differ from those of acute angle-closure glaucoma?
- POAG: Gradual, painless loss of peripheral visual field
| - AACG: Red painful eye, blurred vision, nausea, vomiting, severe ocular pain
94
Why is pilocarpine used in the treatment of acute angle-closure glaucoma?
- Constricts pupil to improve aqueous outflow
| - Prevents iris adhesion to trabecular meshwork
95
What is trabeculectomy?
- Making a hole in the periphery of the iris increasing spaces of trabeculae
96
Outline the pathology of retinal detachment
- Tear in retina
| - Fluid collects in potential space between sensory retina and pigment epithelium
97
What are the clinical features of retinal detachment?
- Visual field loss
- Floaters
- Flashes of light (photopsia)
98
What is the treatment of retinal detachment?
- Laser surgery to scar edge of retinal tear
| - Thereby attaching the retina back to the eye
99
Outline the pathology of retinal pigmentosa
- 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
What is the treatment of retinal pigmentosa?
- Vitamin A supplementation may slow progression
| - Gene therapy is being investigated
101
Identify risk factors in age related macular degeneration
- Smoking
- Hypertension
- Hypercholesterolaemia
- UV exposure
102
Identify two types of AMD
- Non-exudative (dry) with lipofuscin deposits
| - Exudative (wet) AMD with subfoveal choroidal neovascularisation
103
What is the treatment of AMD?
- Vitamins C, E, beta carotene, zinc copper
| - Intravitreal injections of anti-vascular endothelial growth factor such as ranibzumab
104
How are visual fields assessed at bedside?
- Confrontation
| - Comparing the examiner's eye and patient's fields, one eye at a time, quadrant by quadrant
105
Identify two detailed tests of visual fields?
- Goldmann (manual) perimetry testing
| - Humphrey (automated) perimetry testing
106
What is meant by hemianopia?
- When half of visual field is affected
107
What is meant by quandrantanopia?
- When a quadrant of a visual field is affected
108
Lesions of which region produce homonymous field defects?
- 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
Lesions damaging which fibres cause bitemporal defects?
- Lesions damaging the decussating nasal fibres at the optic chiasm
110
Mononuclear field loss is caused by a nerve lesion located at [A] and may be due to [B]
- [A] Optic nerve
| - [B] Optic neuritis
111
BItemporal hemianopia is caused by a lesion located at [A] and may be due to [B]
- [A] Optic chiasm
| - [B] Pituitary tumours
112
Incongruous contralateral homonymous hemianopia is caused by a lesion located at [A] and may be due to [B]
- [A] Optic tract
- [B] Tumour, stroke
or inflammatory disease
113
What type of visual field loss occurs in damage to
[A] Temporal lobe
[B] Parietal lobe
- [A] Contralateral homonymous upper quadrantanopia
| - [B] Contralateral homonymous lower quadrantanopia
114
What is meant by macular sparing and why can damage to the occipital lobe be macular sparing?
- 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
Outline process of phototransduction
- 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
What is the effect of phenylephrine on pupillary diameter?
- Mydriasis (dilation)
| - Since it is an alpha-1 agonist
117
What is the effect of tropicamide on pupillary diameter?
- Mydriasis (dilation)
| - Since it is an M3 antagonist
118
What is the effect of pilocarpine on pupillary diameter?
- Miosis (constriction)
| - Since it is an M3 agonist
119
What is miosis?
- Pupillary constriction
120
Outline the mechanism behind miosis
- 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
What is mydriasis?
- Pupillary dilation
122
Outline the mechanism behind mydriasis
- 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
What is the cause of Horner's syndrome?
- Interruption to sympathetic nerves in the cervical sympathetic chain
- E.g. tumour
124
Outline 3 clinical features of Horner's syndrome
- Ptosis
- Miosis
- Anhydrosis
125
How is a myopic eye corrected?
- Concave lens
- Which diverges light rays
- Enhanced focus of the image on the retina
126
How is a hyperopic eye corrected?
- Convex lens
- Which converges light rays
- Enhanced focus of the image on the retina
127
Identify the two components of the pupillary light reflex
- Direct component mediates constriction of the ipsilateral pupil
- Consensual component mediates constriction of the contralateral pupil
128
What is amblyopia?
- 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
At what age does amblyopia develop and before which age must it be detected and treated to prevent blindness?
- Age 2
| - Age 8
130
Why can strabismus cause amblyopia?
- Misalignment of each eye results in different retinal images being sent to the visual cortex
131
Why does amblyopia not occur in adults? What occurs in adults when a visual image is suppressed?
- The visual cortex pathway are developed
| - Diplopia
132
Which of Brodmann's area are the secondary visual areas located?
- 18 and 19
133
Where is the 'What?' Pathway located and what is it concerned with?
- Medially in association area
- Colour medially
- Faces in the middle region
- Form laterally
134
Where is the 'Where?' Pathway located and what is it concerned with?
- Laterally in association area
| - Movement in contralateral visual hemifield
135
What is felt stigma?
- A change in self identity that is manifested as shame, guilt and withdrawal
136
What is enacted stigma?
- 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
Outline the negative feedback circle of stigma
- 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
What is a virtuous circle in relation to stigma
- 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
Identify five strategies to tackle stigma
- Legislation
- Education
- Language
- Public acknowledgement
- Treatment
140
Outline the Medical Model of Disability
- Disability caused by health condition or impairment
| - By fixing the body, disabled people can participate in society like everyone else
141
Outline the Social Model of Disability
- Distinguishes between impairment (loss of functioning part of body) and disability (meaning society attaches to impairment)
- Three barriers include environment, attitudes and organisations
142
What is Activities of Daily Living and how is it measured?
- Assessment of disability
- How an impairment affects everyday activities
- Measured as elf-report and observation
143
What is sensation?
- The detection of simple properties of stimuli
| - Such as brightness, colour and sweetness
144
What is perception?
- - Detection of objects, their locations, movements and backgrounds
145
What is bottom's up processing?
- Analysis of stimuli into a set of features
- Which are compared to existing sets in the brain
- Recognition occurs if a match occurs
146
What is top-down processing?
- Contextual and based on expectancy
| - People see what they expect or want to see
147
Define attention
- Directing and focusing of perception
| - May be selective, divided or focused and can be negatively affected by stress or fatigue
