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Medicine Year 2 > HNN Topic 20 - Eyes and Vision > Flashcards

HNN Topic 20 - Eyes and Vision Flashcards

1
Q

What is the function of the bipolar cells of the retina?

A

Transmit excitatory and inhibitory signals vertically through the retina

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2
Q

Describe the inner layer of the eyeball

A
  • Retina - light detecting part of the eye
  • 2 layers - neural and pigmented
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3
Q

Describe the features of exudative AMD

A
  • New blood vessels growing under retina from choroid
  • Rapid
  • 10-15% of cases, 90% of cases of severe vision loss in AMD
  • Blood vessels break, bleed and leak fluid, damaging the macula and causing it to lift away from the choroid
  • Metamorphosia - distorted vision, straight lines appear wavy
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4
Q

Why is the visual field of both eyes limited in the inferior medial quadrant?

A

Lateral side of the nose blocks vision in this area

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5
Q

List the steps in diagnosis of AMD

A
  1. Visual acuity test
  2. Fundus fluorescein angiogram
  3. Optical coherence tomography
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6
Q

What is optical coherence tomography?

A
  • Low powered laser interferometry
  • Generates detailed cross-sectional image of retina
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7
Q

Describe how neovascularisation causes visual disturbances in AMD

A
  1. Choroidal neovascularisation begins in choroid
  2. CNV enters gaps in Bruch’s membrane, vessels begin growing in subretinal space
  3. Subretinal haemorrhage, retinal distortion
  4. Intraretinal haemorrhage, intraretinal fluid
  5. Thicking and elevation of macula
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8
Q

List the layers of the eyeball

A
  1. Fibrous
  2. Vascular
  3. Inner
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9
Q

How do genetics contribute to AMD?

A
  • Polymorphisms in complement factor H gene strongly linked to AMD - complement factor H regulates inflammation, prevents complement attack of own cells
  • Othe genes
    • Complement - CFB, CF1, C2/3
    • Lipids - genes for HDL and LDL
    • ECM - collagen and matrix metalloproteinase
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10
Q

What is the result of a lesion to Meyer’s loop

A

Homonymous upper quadrantanopia - loss of vision in same upper quadrant of visual field in both eyes

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11
Q

What anatomical landmark does the calcarine sulcus indicate?

A

Primary visual cortex

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12
Q

Describe the structural features of the retina seen during an ophthalmoscopy

A
  • Macula - slightly off-centre highly pigmented area
    • Depression in central 500 microns of macula = fovea
    • High concentration of cone cells - high acuity vision (reading, facial recognition)
    • No blood vessels - dependent on choroid for O2 and metabolic support
  • Optic disc - area where optic nerve leaves retina, no light detecting cells
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13
Q

Describe the location of the eyeball

A
  • Bilateral spherical organ
  • Lies in bony orbit - bony cavity within facial skeleton
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14
Q

Describe the structure and function of the iris

A
  • Circular structure with aperture in centre (pupil) - diameter altered by smooth muscle fibres within iris, innervated by ANS
  • Between lens and cornea
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15
Q

Describe the pathogenesis of AMD

A
  • Photoreceptors continue to produce photosensitive pigment throughout life
  • Ends of photoreceptor cells decay and are removed by retinal pigment epithelium
  • End products accumulate, causing drusen
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16
Q

Describe how visual acuity tests are carried out

A
  • Recorded as the distance chart is read/distance at which it should be read
  • 6/6 is normal - reads at 6m what should be seen at 6m
  • 6/12 - reads at 6m what should be seen at 12m
  • 6/36 - reads at 6m what should by seen at 36m
  • Wear distance glasses if needed, 6m from chart, one eye at a time, if vision not perfect use pinhole
  • If vision <6/60 - count fingers, hand motions, light perception
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17
Q

Describe the appearance of the retina in exudative AMD

A

Neovascularisation, leaking fluid

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18
Q

Describe the path of light as it enters the eyeball

A
  1. Incident light passes through cornea to enter eye
  2. Moves through aqueous humour of anterior segment
  3. Passes through lens
  4. Passes through vitreous humour of posterior segment
  5. Hits retina
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19
Q

What is the result of an optic radiation lesion?

A

Homonymous hemianopia

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20
Q

Describe ion transport in rod cells in normal conditions (no light)

A
  • Extracellular fluid surrounding rod cells is high in sodium ions and low in potassium ions, opposite in cells - maintained by sodium/potassium pump
  • In resting state K moves out - negative charge inside
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21
Q

What is the result of a complete optic nerve lesion?

A

Blindness in that eye

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22
Q

What is the function of the horizontal cells in the retina?

A

Inhibitory neurons that provide lateral inhibition - increases spatial resolution (i.e. visual contrast)

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23
Q

How is visual field tested?

A

Goldmann Perimetry test - outline shows borders of peripheral vision

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24
Q

What are the ganglion cells of the retina?

A

Axons from optic nerve after exiting through the optic disc

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25
Q

What causes optic nerve lesions?

A
  • Acute optic neuritis (inflammation of optic nerve) - Multiple Sclerosis
  • Indirect traumatic optic neuropathy
  • Optic atrophy - loss of nerve fibres e.g. due to ischaemia
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26
Q

Are dendrites afferent or efferent neuronal cell processes?

A

Afferent - recieve information

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27
Q

Describe the sequence of events which occurs when light hits a rod cell

A
  1. Light hits rod cell, absorbed by rhodopsin
  2. Rhodopsin breaks down into scotopsin and 11 cis-retinal = bleaching
  3. 11 Cis-retinal absorbs photon, changes to trans-retinal
  4. Trans-retinal activates the enzyme scotopsin
  5. Large amount of G protein transducin produced, activates enzyme phosphodiesterase
  6. Phosphodiesterase hydolyses cGMP which stops the flow of sodium ions inside rod cells - causes hyperpolarisation of cells
  7. Hyperpolarised rod cells transmit the neural signal to bipolar cells
  8. Bipolar cells, amacrine cells and ganglion cells process the neural signal and generate action potentials to transmit to the brain via the optic nerve
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28
Q

Describe the features of atrophic AMD

A
  • Slow, blurring
  • 80-90% of cases of AMD
  • Small white/yellow deposits called drusen form on the retina, beneath the macula, causing it to deteriorate or degenerate over time
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29
Q

Describe the contents of the left and right optic tracts

A
  • Right optic tract - temporal fibres from right eye and nasal fibres from left eye (left hemifield)
  • Left optic tract - temporal fibres from left eye and nasal fibres from right eye (right hemifield)
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30
Q

Describe the mechanism of action of cone cells

A
  • Similar neural activity to rod cells
  • 3 different types ofo cone cell (each contains different photopigment), sensitive to red, green or blue
  • Iodopsin is photpigment, composed of 11 cis-retinal + photopsin
  • Final percieved colour is combination of all three types of cone cells depending on level of stimulation
  • White = combination of all cone cells
  • Black = absence of light
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31
Q

Which cranial nerves pass through the cavernous sinus?

A

Oculomotor, trochlear and abducens nerves

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32
Q

Describe the main projections of the extra-geniculate pathways

A
  • Pretectal nucleus of midbrain - pupillary light reflex
  • Superior colliculus of midbrain - coordinated reflex head and eye movements in response to visual stimulus
  • Suprachiasmatic nucleus of hypothalamus - regulates day-night cycle, circadian rhythm
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33
Q

How are the visual fields perceived within the eye?

A
  • Image is reversed and inverted in the eye
  • Visual field of each eye divided into nasal (medial) and temporal (lateral)
  • Fields cross and are recieved by opposite sides of the retina
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34
Q

Define homonymous hemianopia

A

Loss of one side of the visual field - same side in both eyes

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35
Q

Describe the structure of rod cells

A
  • Light sensitive pigment = rhodopsin
    • Combination of protein scotopsin and light sensitive small molecule retinal
    • Retinal is a carotenoid molecule, derivative of Vitamin A (retinol)
    • Retinal exists in cis- and trans- forms according to light condition
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36
Q

How long are the optic nerves?

A

Approx 50mm

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37
Q

What sign can be see during an ophthalmoscopy which indicates raised intracranial pressure?

A

Papilloedema

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38
Q

Explain the psychosocial effects of visual impairment

A
  1. Economic - financial, unemployment, increased care required
  2. Indepence - domestic, navigation
  3. Communication + social - non-verbal communication, TV/film/media
  4. Psychological - isolation, anxiety, depression
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39
Q

List the visual pathways

A
  • Geniculate pathway
    • To occipital lobe, for concious visual processing
  • Extra-geniculate pathways
    • To midbrain for reflex responses
    • To hypothalamus for modulation of day-night cycles
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40
Q

Describe the appearance of the retina in atrophic AMD

A

Drusen deposists, areas of retinal pigment epithelium thinning/depigmentation

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41
Q

Describe the structure and function of the choroid

A

Connective tissue and blood vessels, nourishes outer layer of retina

42
Q

What is the result of a visual cortex lesion?

A

Homonymous hemianopia

43
Q

What causes RAPD?

A

Disease of optic nerve or retina e.g. optic neuritis, large retinal detachment

44
Q

Describe the decussation of the optic nerves at the optic chiasm

A
  • 50-60% decussation
  • Fibres from nasal retina cross, fibres from temporal retina don’t cross
45
Q

Define hippus

A

Normal pupillary response to light - eye constricts rapidly, dilates a little then constricts to a constant diameter

46
Q

What is the result of a partila optic nerve lesion?

A

Ipsilateral scotoma

47
Q

Describe convergence in the eye

A
  • Binocular vision - two eyes percieve single image
  • Two eyeballs turn slightly inwards to focus on close objects so both images fall on corresponding points on the retina at the same time
48
Q

Describe accommodation of the lens for a near object

A

Contraction of ciliary muscles, less tension on suspensory ligaments, lens thicker and rounder

49
Q

What is the afferent pathway of the pupillary light response?

A

Optic nerve

50
Q

Describe the normal pupillary response to light

A

Constriction of that pupil (direct response) and of the contralateral pupil (consensual response)

51
Q

List the major worldwide causes of blindness

A
  1. Cataract
  2. Glaucoma
  3. AMD
  4. Corneal scar
  5. Diabetic retinopathy
  6. Childhood blindness
  7. Trachoma
52
Q

List the types of glial cells in the retina

A
  1. Muller cells - predominant
  2. Astrocytes - mostly in ganglion cell layer + nerve fibre layer
  3. Microglia - scattered throughout
53
Q

Describe the components of the fibrous layer of the eyeball

A
  • Sclera and cornea - continuous, provide shape and support
  • Sclera - 85%, attachment of extraocular muscles, white of eye
  • Cornea - transparent, located centrally at front of eye, refract light entering eye
54
Q

What causes visible distortion of the optic disc?

A

Papilloedema or optic neuritis (inflammation of the optic nerve)

55
Q

What is the functional contact point between two neurons called?

A

Synapse

56
Q

Describe the structure and function of the ciliary body

A
  • Ciliary muscle and ciliary process
  • Ciliary muscle - smooth muscle attached to the lens by ciliary process, controls shape of the lens, forms aqueous humour
57
Q

What is the efferent pathway of the pupillary light response?

A

Oculomotor nerve

58
Q

Describe the pathway which leads to constriction of the pupils in response to light

A
  • Parasympathetic pathway
  • Pre-tectal nucleus projects bilaterally to Edinger-Westphal nuclei
  • Preganglionic neurons travel on oculomotor nerve, synapse on ciliary ganglion
  • Postganglionic neurons act on pupillary sphincter to constrict the pupils
  • Both pupils contract as the optic tracts contain fibres from both eyes
59
Q

Which parts of the retina are responsible for vision?

A
  • Anteriorly - only pigmented layer, non-visual part of retina
  • Posteriorly/laterally - both layers, optic part of retina
60
Q

What promotes neovascularisation in AMD?

A

VEGF - vascular endothelial growth factors

Up-regulation promotes growth of new vessels

61
Q

Describe the appearance of the lateral geniculate nucleus

A

6 layers of grey matter with alternating white matter - striped appearance

62
Q

Describe the epidemiology of blindness

A
  • 0.6% of population
  • Mostly affects >50 year olds
  • Higher prevelance in developing countries/poor populations
63
Q

What suggests an efferent limb problem in the pupillary light response?

A

Efferent limb problem - no response in one eye but direct + consensual response in other eye

64
Q

Describe the coverings of the optic nerve

A
  • Dura mater, arachnoid mater and pia mater of the meninges form the outer, intermediate and inner sheaths of the optic nerve
  • Subarachnoid space between the intermediate and inner sheaths
65
Q

What are the requirements for legal blindness?

A

Severely sight impaired (blind) = 3/60

Sight impaired = 3/60-6/60

66
Q

Compare Ranibizumab and Bevacizumab

A
  • Ranibizumab - licensed, very costly (£750/dose), monthly injections (inconvenient, uncomfortable + risky)
  • Bevacizumab - unlicensed, much cheaper (£49/dose), dose as required, just as effective
67
Q

List the types of age-related macular degeneration

A
  1. Exudative (wet)
  2. Atrophic (dry)
68
Q

List the steps in examining the pupils

A
  1. Inspect pupils - look for asymmetry or irregularity
  2. Check the direct and consensual reactions to light
  3. Swinging light test for RAPD
  4. Accommodation-convergence reflex
69
Q

Describe and compare the two types of synapse

A
  • Grey type 1
    • Asymmetrical - presynaptic and postsynaptic membranes are different
    • Spherical synaptic vesicles - excitatory e.g. glutamate
  • Grey type 2
    • Symmetrical - presynaptic and postsynaptic membranes are similar
    • Elliptical synaptic vesicles - inhibitory e.g. GABA
70
Q

What is the result of a bilateral macular cortex lesion?

A

Bilateral central scotoma - blind spot in centre of visual field of both eyes

71
Q

Describe the treatment of AMD

A
  • Anti-VEGF drugs - Ranizumab, Bevacizumab, Aflibercept
  • Ranizumab used -
    • Intravitreal injections
    • Sterile procedure - needs clean room
    • Repeated monthly for 3 doses, then as required
72
Q

What is the function of the amacrine cells of the retina?

A

Many functional diverse subtypes that assisst in interpreting visual signals before they leave the retina

73
Q

How is a fundus fluorescein angiogram performed?

A
  • Inject fluorescein intravenously
  • Fluorescein bound to albumin - remains within normal capillaries due to blood-retinal barrier
  • Use blue flash and yellow filter to see details of retinal circulation
74
Q

What causes lesions of the optic tract?

A
  • Tumours
  • Trauma
  • Aneurysms of posterior cerebral artery
75
Q

Describe the components of the anterior and posterior chamber

A
  • Filled with aqueous humour
    • Plasma-like fluid that nourishes and protects the eye
    • Produced constantly, drains via trabecular meshwork
76
Q

Describe refraction of light in the eye

A
  • Light rays meet the convex surfaces of the cornea and lens and are angulated (via convergence) to a focal point on the retina
  • Cornea is responsible for most of the refractive power, but changing the shape of the lens allows refractive power to be altered
77
Q

How does AMD cause blindness?

A
  • Blood vessels and scar tissue grow under retina
  • Leaking vessels cause retinal oedema
  • Blocks transport of O2 and nutrients from choroid
  • Eventual scarring causes destruction of photoreceptors
78
Q

Describe the pigmented layer of the retina

A
  • Outer layer
  • Attached to choroid layer, supports neural layer
  • Around whole inner surface of eye
79
Q

Where do the visual pathways originate?

A
  • Originates in retina due to stimulation of rod and cone cells, which activates bipolar/ganglion cells
  • Magnocellular (M) cells - sensitive to movement and low contrast
  • Parvocellular (P) cells - sensitive to fine details and colours
80
Q

Describe the histological arrangement of the macula

A
  1. Ganglion cells (send neural signal to brain via optic nerve)
  2. Bipolar cells
  3. Photoreceptors (respond to light)
  4. Retinal pigment epithelium
  5. Choroid
81
Q

List the types of neuron in the retina

A
  1. Photoreceptor cells - rods and cones
  2. Bipolar cells
  3. Ganglion cells
  4. Horizontal cells
  5. Amacrine cells
82
Q

What is the swinging flashlight test used for?

A

Can identify asymmetry of afferent input in pupillary light reflex - Relative Afferent Pupil Defect (RAPD)

83
Q

How is the shape of the lens changed?

A

Suspensory ligaments attach the lens to the ciliary muscles and through contraction and relaxation allows changes in the shape of the lens to increase or decrease refractive power

84
Q

What is the function of rod cells?

A
  • Predominant photoreceptor
  • Don’t detect colour
  • Poor resolution
  • More sensitive than cones
85
Q

Describe the neural layer of the retina

A
  • Inner layer
  • Contains photoreceptors - light detecting
  • Posteriorly and laterally in the eye
86
Q

What is the function of cone cells?

A
  • Colour vision
  • Sparse in comparison to rods, except in fovea of macula
  • High resolution - high visual acuity
  • Dark adaption much faster than rods
87
Q

What is the simplest pathway which causes transmission of signals by the optic nerve?

A

3-neuron chain - photoreceptor cell to bipolar cell to ganglion cell

88
Q

What passes through the blind spot and makes it blind?

A

Retinal ganglion cell axons travelling to the optic nerve

89
Q

What is the result of an optic chiasm lesion?

A

Bitemporal hemianopia - loss of temporal visual field in both eyes

90
Q

List the causes of AMD

A
  • Environmental factors - smoking causes 30% of cases
  • Age - rare in people <70%
  • Diet? - possible that high doses of Vitamin A, C and zinc may be protective
  • Family history - relative of those with AMD at greater risk
91
Q

Where are the anterior and posterior chambers of the eyeball?

A
  • Anterior is between cornea and iris
  • Posterior is between iris and ciliary body
92
Q

Where is the lens in the eyeball?

A

Anterior, between vitreous humour and pupil

93
Q

Describe the vision loss caused by AMD

A

Central vision loss and metamorphosia

94
Q

List the components of the vascular layer of the eyeball

A
  1. Choroid
  2. Cillary body
  3. Iris
95
Q

What shows a RAPD during the swinging flashlight test?

A

When moving light from one eye to the other, pupil of eye which light is shining on dilates

96
Q

Describe the geniculate visual pathway after leaving the retina

A
  1. Nerve fibres of ganglion cells from both eyes carry impulse along two optic nerves
  2. Optic nerves meet at optic chiasm
  3. Optic nerve form optic tracts after crossing at chiasm
  4. Synapses with neurons in the thalamus called lateral geniculate pathways
  5. Project through optic radiation, sweeps around lateral ventricle to the primary visual cortex on the medial side of the occipital lobe
97
Q

What is the function of the lens?

A
  • Refraction of light onto the retina
  • Shape altered by ciliary body - alters refractive power
  • Responsible for accommodation + convergence
98
Q

What causes optic chiasm lesions?

A
  • Tumours (pituitary adenoma, meningioma)
  • Aneurysm
99
Q

What mediates the changes in the shape of the lens?

A

Parasympathetic nerve fibres travelling on the oculomotor nerve

100
Q

Describe the accommodation convergence reflex

A
  • Pupil constriction and converge of the eyes when looking from a distant object to a close one
  • Pupil constriction (constrictor pupillae)
  • Lens accommodation (ciliary muscles)
  • Convergence of eyes (contraction of both medial rectus muscles)
  • Afferent pathway = optic nerve
  • Efferent pathway = occulomotor nerve
101
Q

Describe accommodation of the lens for a distant object

A

Ciliary muscles relax, more tension on suspensory ligaments, lens thinner and flatter

102
Q

Describe the arterial supply of the eyeball

A
  • Mostly via the ophthalmic artery (branch of internal carotid, arises immediately distal to cavernous sinus)
  • Gives rise to many branches, central artery of retina most important - supplies internal surface of retina

Medicine Year 2 (41 decks)

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