Week 6 Flashcards
(152 cards)
1
Q
What is leukoplakia?
A
A white patch or plaque that cannot be scraped off and cannot be characterised clinically or pathologically as any other disease
2
Q
Where is leukoplakia most often found?
A
- Vermilion border of the lower lips
- Buccal mucosa
- Hard and soft palates
- Less frequently on the floor of the mouth and intramural sites
3
Q
Describe leukoplakia:
A
- Approximately 33% of the world’s population have leukoplastic lesions
- Somewhere between 5 and 25% of these lesions are premalignant
- Most frequent among older men
- Appear as localised, sometimes multifocal or even diffuse, smooth or roughened, leathery, white, discrete areas of mucosal thickening
- All lesions are considered precancerous until proven otherwise by histological evaluation
4
Q
Describe erythroplakia:
A
- Less common than leukoplakia
- Characterised by the presence of red, velvety patches of epithelial atrophy and pronounced dysplasia
- Seen mainly in elderly males on the buccal mucosa or the palate
- Malignant transformation is much more common than with leukoplakia
- Development is associated with heavy tobacco use
5
Q
What are the majority of cancers in head and neck?
A
95% are head and neck squamous cell carcinomas (HNSCCs), the remainder includes adenocarcinomas (of salivary gland origin), melanomas, various carcinomas and other rarities
6
Q
What are HNSCCs derived from?
A
Lining epithelium of the mouth, and may arise from existing dysplasia (such as leuko or erythroplakia)
7
Q
What are the factors involved in pathogenesis of HNSCCs?
A
- Smoking
- Alcohol
- HPV
- Genetics
- Sunlight
- Nutritional deficiency
8
Q
How can HPV cause HNSCC?
A
- At least 50% of oropharyngeal cancers, particularly those involving the tonsils, the base of the tongue, and the oropharynx harbour oncogenic variants of HPV
- Predicted that the incidence of HPV-associated HNSCC will surpass that of cervical cancer in the next decade
- This is due to the anatomic sites of origin (tonsillar crypts base of tongue and oropharynx) are not readily accessible or amenable to cytologic screening (unlike the cervix)
- Should be noted, patients with HPV-positive HNSCC do netter than those with HPV-negative tumours
- HPV vaccine is not yet licensed to treat or prevent HNSCC
9
Q
What is the pathology of HNSCC?
A
- Macroscopically, there are raised nodular lesions and central ulceration with hard raised edges
- Microscopically, the tumour is typically well-differentiated and keratinising
- Sites include:
- lips (most common)- usually recognised early and amenable to surgery
- tongue- typically occurring on the lateral border of the anterior two-thirds
- cheek or floor of mouth (less common in UK)- generally asymptomatic, resulting in extensive local invasion making surgical removal difficult
10
Q
Describe the histological progression of oral cancer:
A
- Normal
- Hyperplasia/hyperkeratosis
- Mild/moderate dysplasia
- Severe dysplasia/carcinoma in situ
- Squamous cell carcinoma
11
Q
Describe the superficial lymph nodes of the head and neck:
A
- Form a ring around the head
- Responsible for the lymphatic drainage of the face and scalp
- Lymphatic flow from these superficial lymph nodes passes in several directions
- Occipital and postauricular nodes -> superficial cervical nodes
- Preauricular, submandibular and submental -> deep cerival nodes
12
Q
Describe the occipital nodes:
A
- Near the attachment of the trapezius muscle to the skull
- Associated with the occipital artery
- Lymphatic drainage is from the posterior scalp and neck
13
Q
Describe the postauricular nodes:
A
- Posterior to the ear near the attachment of the SCM
- Associated with the posterior auricular artery
- Lymphatic drainage is from the posterolateral half of the scalp
14
Q
Describe the preauricualr nodes:
A
- Anterior to ear
- Associated with the superficial temporal and transverse facial arteries
- Lymphatic drainage is from anterior surface of the auricle, anterolateral scalp, the upper half of the face, eyelids and cheeks
15
Q
Describe the submandibular nodes:
A
- Inferior to the body of the mandible
- Associated with the facial artery
- Lymphatic drainage is fro structures along the path of the facial artery as high as the forehead, as well as the gingivae, teeth and tongue
16
Q
Describe the submental nodes:
A
- Inferior and posterior to the chin
- Lymphatic drainage is from the central part of the lower lip, chin, floor of the mouth, tip of the tongue and lower incisor teeth
17
Q
Describe the superficial cervical nodes:
A
- Collection of lymph nodes along the external jugular vein on the superficial surface of the SCM
- Primarily receive lymphatic drainage from the posterior and posterolateral regions of the scalp through the occipital and post-auricular nodes
- Send lymphatics in the direction of the deep cervical nodes
18
Q
Describe the deep cervical nodes:
A
- Collection of lymph nodes that form a chain along the internal jugular vein
- Divided into upper and lower groups where the intermediate tendon of the omohyoid muscle crosses the common carotid artery and internal jugular vein
- Eventually receive all lymphatic drainage from the head and neck either directly or through regional groups of nodes
- From the deep cervical nodes, lymphatic vessels for the right and left jugular trunks, which empty into the right lymphatic duct on the right side or thoracic duct on the left
19
Q
What is the most superior deep cervical node?
A
Jugulodigastric, which receives lymphatic drainage from the tonsils and tonsillar region
20
Q
What does the jugulo-omohyoid node receive lymphatic drainage from?
A
The tongue
21
Q
Where do the intrinsic muscles of the tongue sit?
A
Originate and insert within the substance of the tongue
22
Q
What are the intrinsic muscles of the tongue?
A
- Superior longitudinal
- Inferior longitudinal
- Transverse
- Vertical
23
Q
How do the intrinsic muscles of the tongue work?
A
- Alter the shape of the tongue by;
- lengthening and shortening it
- curling and uncurling its apex and edges
- flattening and rounding its surface
- Work in pairs or one at a time
- Contribute to precision movements of the tongue required for speech, eating and swallowing
24
Q
What are the extrinsic muscles of the tongue?
A
Genioglossus, hyoglossus, styloglossus and palatoglossus
25
Describe genioglossus:
- Thick fan-shaped
- Make a substantial contribution to the structure of the tongue
- Occur on each side of the midline septum that separates left and right halves of the tongue
- Depresses the central part of the tongue
- Sticks out the tongue
- Innervated by CN XII
26
Describe hyoglossus:
- Thin quadrangular muscles lateral to the genioglossus muscles
- Depresses the tongue
- Innervated by CN XII
27
Describe styloglossus:
- Originates from the anterior surface of the styloid process of the temporal bone
- Retracts the tongue and pulls the back of the tongue superiorly
- Innervated by CN XII
28
Describe palatoglossus:
- Muscles of the soft palate
- Elevates the back of the tongue
- Moves the palatoglossal arches of mucosa towards the midline
- Depresses the soft palate
- Innervated by CN X
29
What is the larynx?
- Short passageway that connects the laryngopharynx with the trachea
30
Where is the larynx?
Lies in the midline of the neck anterior to the oesophagus between C4-C6
31
What is the wall of the larynx composed of?
Nine pieces of cartilage
- Single
- thyroid
- epiglottis
- cricoid
- Paired
- arytenoid
- cuneiform
- corniculate
32
What is the importance of the arytenoid cartilage?
Influences changes in position and tension of the vocal folds
33
What is the function of the extrinsic muscles of the larynx?
Connect the cartilages to other structures in the throat
34
What is the function of the intrinsic muscles of the larynx?
Connect the cartilage to one another
35
What is the cavity of the larynx?
- Cavity of the larynx is a space that extends from the entrance into the larynx down the inferior border of the cricoid cartilage
36
What is the portion above the vocal folds called?
Vestibule of the larynx
37
Describe the thyroid cartilage:
- Consists of two fused plates of hyaline that form the anterior wall of the larynx and give it a triangular shape
- Present in both males and females
- Larger in males due to the influence of male sex hormones on its growth during puberty
38
What ligament connects the thyroid cartilage to the hyoid bone?
Thyrohyoid membrane
39
What is the epiglottis?
Large, leaf shaped piece of elastic cartilage
40
What covers the epiglottis?
Epithelium
41
What is the stem of the epiglottis?
The tapered inferior portion that is attached to the anterior rim of the thyroid cartilage and hyoid bone
42
What is the leaf of the epiglottis?
Broad superior portion that is attached to the anterior rim of the thyroid cartilage and hyoid bone
43
Describe the epiglottis movements:
- During swallowing -> pharynx and larynx rise
- Elevation of the pharynx widens it to receive food or drink
- Elevation of the larynx causes the epiglottis to move down and form a lid over the glottis, closing it off
- Closing of the larynx in this way during swallowing routes liquids and foods into the oesophagus and keeps them out the larynx and airways
- When small particles of dust, smoke, food or liquids pass into the larynx -> cough reflex occurs
44
What does the glottis consist of?
A pair of folds of mucous membrane, vocal folds in the larynx and the space between them (rima glottidis)
45
Describe the cricoid cartilage:
- Ring of hyaline cartilage that forms the inferior wall of the larynx
- Attached to the first ring of cartilage of the trachea by the cricotracheal ligament
46
What connects the thyroid and cricoid cartilage?
Cricothyroid ligament
47
What is the clinical significance of the cricothyroid ligament?
Landmark for making an emergency tracheotomy
48
Describe the arytenoid cartilages:
- Triangular pieces of mostly hyaline cartilage
- Located at the posterior, superior border of the cricoid cartilage
- Form synovial joints with the cricoid cartilage and have a wide range of mobility
49
Describe the corniculate cartilages:
- Horn-shaped pieces of elastic cartilage
| - Located at the apex of each arytenoid cartilage
50
Describe the cuneiform cartilages:
- Club-shaped elastic cartilages
- Anterior to the corniculate cartilages
- Support the vocal folds and lateral aspects of the epiglottis
51
What is the lining of the larynx superior to the vocal folds?
Nonkeratinised stratified squamous epithelium
52
What is the lining of the larynx inferior to the vocal folds?
Pseudo-stratified ciliated columnar epithelium consisting of;
- ciliated columnar cells
- goblet cells
- basal cells
53
Describe movement of dust and trapped particles in the larynx:
- Mucus produced by the goblet cells helps trap dust not removed in the upper passages
- Cilia in the upper respiratory tract move mucus and trapped particles down the pharynx
- Cilia in the lower respiratory tract move mucus and trapped particles up towards the pharynx
54
What does the mucous membrane of the larynx consist of?
Two pairs of folds:
- superior pair -> ventricular folds (fasle vocal folds)
- inferior pair -> vocal folds (true vocal folds)
55
What is the space between the vocal folds known as?
Rima vestibule
56
What is the laryngeal sinus?
A lateral expansion of the middle portion of the laryngeal cavity inferior to the ventricular folds and superior to the vocal folds
57
What is the function of the ventricular folds?
- Ventricular folds do not function in voice production
- When the ventricular folds are brought together, they function in holding the breath against pressure in the thoracic cavity, such as might occur when a person strained to lift a heavy object
58
What lies deep to the mucous membrane of the vocal folds?
Bands of elastic ligaments stretched between the rigid cartilage of the larynx
59
Where do the intrinsic laryngeal muscles attach?
To both the right cartilages and the vocal folds
60
Describe voice production:
- When the muscles contract, they move the cartilages which pulls the elastic ligaments tight, and this stretches the vocal folds out into the airways so that the rima glottidis is narrowed
- Air passing through the larynx vibrates the folds and produces sound by setting up sound waves in the column of air in the pharynx, nose and mouth
- Variation in pitch of the sound is related to the tension of the vocal folds
- Greater the pressure of air: louder the sound produced by vibrating vocal folds
61
What are the three layers making up the eye?
Fibrous tunic, vascular tunis and the retina
62
What does the fibrous tunic consist of?
Anterior cornea and posterior sclera
63
Describe the cornea:
- Transparent coat that covers the iris
- Curved: helps focus light on the retina
- Central part of the cornea receives oxygen from the outside air -> contacts must be permeable to permit oxygen through them
64
What does the outer surface of the cornea consist of?
Nonkeratinised stratified squamous epithelium
65
What does the middle coat of the cornea consist of?
Collagen fibres and fibroblast
66
What does the inner coat of the cornea consist of?
Simple squamous epithelium
67
Describe the sclera:
- White of the eye
- Layer of dense CT
- Composed mainly of collagen and fibroblasts
- Covers the entire eyeball except for the cornea
- Gives shape to the eyeball
- Makes it more rigid
- Protects the inner parts
- Serves as a site for attachment for extrinsic eye muscles
68
What is at the junction of the sclera and cornea?
Scleral venous sinus, into which the aqueous humour drains
69
What is the vascular tunic?
Middle layer of the eyeball
70
What is the vascular tunic composed of?
Three parts: choroid, ciliary body and iris
71
Describe the choroid:
- Highly vascularised
- Posterior portion of the vascular tunic
- Lines most of the internal surface of the sclera
- Numerous blood vessels supply the posterior surface of the retina
- Also contains melanocytes that produce melanin which causes this layer to appear dark brown in colour
- Melanin absorbs stray light rays -> prevents reflection and scattering of light within the eyeball
- As a result, image cast on the retina by the cornea remains sharp and clear
72
Describe the ciliary body:
- In the anterior portion of the vascular tunic, the choroid becomes the ciliary body
- Extends from the ora serrata, the jagged anterior margin of the retina, to a point just posterior to the junction of the sclera and cornea
- Appears dark in colour because of melanin
- Consists of ciliary processes and ciliary muscle
73
Describe the ciliary processes:
- Protrusions or folds on the internal surface of the ciliary body
- Contain blood capillaries that secrete aqueous humour
- Extending from the ciliary process are zonular fibres that attach to the lens
- Fibres consist of thin, hollow fibrils that resemble elastic CT fibres
74
Describe the ciliary muscle:
- Circular band of smooth muscle
- Contraction of relaxation of the ciliary muscle changes the tightness of the zonular fibres, which alters the shape of the lens, adjusting it for near or far vision
75
Describe the iris:
- Coloured portion of the eyeball
- Shaped like a flattened donut
- Suspended between the cornea and the lens
- Attached at its outer margin to the ciliary processes
- Contains melanocytes and circular and radial smooth muscle fibres
- Regulates the amount of light entering the eyeball through the pupil
76
What determines eye colour?
Amount of melanin in the iris:
- large amount of melanin -> brown to black
- moderate concentration of melanin -> green
- low concentrations -> blue
77
Describe the pupil:
- Pupil appears black because of the heavily pig ended back of the eye (choroid and retina )
- When light is directed into the pupil, reflected light is red because of the blood vessels on the surface of the retina
- Autonomic reflexes regulate pupil diameter in response to light levels
78
Describe constriction of the pupil:
- Bright light stimulates eye
- Parasympathetic fibres of CN III stimulate the circular muscles or sphincter pupillae of the iris to contract
- This leads to constriction
79
Describe dilation of the pupil:
- Dim light stimulates eye
- Sympathetic neurons stimulate the radial muscles of dilator pupillae of the iris to contract
- This leads to dilation
80
Describe the retina:
- Inner layer of the eyeball
- Lines the posterior three-quarters of the eyeball
- Beginning of the visual pathway
- Surface of the retina is the only place in the body where blood vessels can be viewed directly and examined for pathological changes
81
What is the optic disc?
This site where the optic nerve exits the eyeball
82
What travels with the optic nerve?
The central retinal artery, a branch of the ophthalmic artery, and the central retinal vein
83
What does the central retinal artery supply?
Branches fan out to nourish the anterior surfaces of the retina
84
What does the central retinal vein drain?
Blood from the retina through the optic disc
85
What does the retina consist of?
A pigmented layer and a neural layer
86
Describe the pigmented layer:
- Sheet of melanin-containing epithelial cells
- Located between the choroid and neural part of the retina
- Melanin in the pigmented layer helps absorb stray light rays
87
Describe the neural layer:
- Multilayered outgrowth of the brain
| - Processes visual data extensively before sending nerve impulses into the axons that form the optic nerve
88
What are the three layers of retinal neurons?
- Photoreceptive layer
- Bipolar cell layer
- Ganglion cell layer
89
What zones separate the retinal neurons?
Outer and inner synaptic layers
90
Describe light passage in the neural layer:
- Light passes through the ganglion and bipolar cell layers and both synaptic layers before it reaches the photoreceptive layer
91
What other cells are present in the bipolar layer?
Amacrine and horizontal cells, which form laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells
92
Describe photoreceptor cells:
- Specialised cells that begin the process by which light rays are converted to nerve impulses
- Rods and cones
- From photoreceptors, information flows through the outer synaptic layer to bipolar cells and then from bipolar cells through the inner synaptic layer to ganglion cells ganglion cells
93
Describe rod cells:
- Allow vision in dim light
- Do not provide colour vision
- Black, white, and all shades of grey
94
Describe cone cells:
- Stimulated by brighter lights
- Produce colour vision
- Three types of cones: blue, green and red
- Colour vision results from the stimulation of various combinations of these types of cones
95
Where do axons of ganglion cells extend?
Posteriorly to the optic disc and exit the eyeball as the optic nerve
96
What is the macula lutea?
The exit centre of the posterior portion of the retina, at the visual axis of the eye
97
What is the fovea centralis?
- A small depression in the centre of the macula lutea that contains only cones
- Layers of bipolar and ganglion cells do not cover the cones here and are displaced to the periphery of the fovea
- Fovea -> area of highest visual acuity
98
Describe the lens:
- Behind the pupil and iris and within the cavity of the eyeball
- Within the cells of the lens are proteins called crystallins, arranged like layers of an onion, which make up the refractive media of the lens, which is normally perfectly transparent and avascular
- Enclosed by a clear CT capsule and held in position by encircling zonular fibres which attach to the ciliary processes
- Help focus images on the retina to facilitate clear vision
99
What does the anterior cavity consist of?
Two chambers, anterior and posterior
100
Where is the anterior chamber?
Lies between the cornea and iris
101
Where is the posterior chamber?
Lies behind the iris and inferno of the zonular fibres and lens
102
What fills both anterior and posterior chambers?
Aqueous humour: transparent watery fluid that nourishes the lens and cornea
103
Describe the flow of aqueous humour:
- Continually filters out of blood capillaries in the ciliary processes of the ciliary body and enters the posterior chamber
- It flows forwards between the iris and the lens, through the pupil, and into the anterior chamber
- From the anterior chamber, aqueous humour drains into the scleral venous sinus and into the blood
- Completely replaced about every 90 mins
104
Describe the vitreous chamber:
- Larger
- Posterior cavity of the eyeball
- Lies between the lens and retina
105
Describe the vitreous body:
- Transparent jellylike substance that holds the retina against the choroid, giving the retina an even surface for the reception of clear images
- Formed during embryonic life and consists mostly of water, collagen fibres and hyaluronic acid
- Vitreous body also contains phagocytic cells that remove debris -> keeps this part of the eye clear for unobstructed vision
106
What is the hyaloid canal?
A narrow channel that runs through the vitreous body from the optic disc to the posterior aspect of the lens
107
Describe intraocular pressure:
- Produced mainly by the aqueous humour and partly by the vitreous body
- Normally around 16 mmHg
- Intraocular pressure maintains the shape of the eyeball and prevents it from collapsing
108
Describe the general structure of photoreceptors:
- Rods and cones were named for the different appearance of the outer segment, the distal end next to the pigmented layer
- Outer segments of rods are cylindrical
- Transduction of light energy into a receptor potential occurs in the outer segment of both rods and cones
- In cones, the plasma membrane is folded back and forth in a pleated fashion
- In rods, the pleats pinch off from the plasma membrane to form discs
109
Where and what are photopigments?
Photopigments are integral proteins in the plasma membrane of the outer segments
110
What does the outer segment of each rod contain?
- A stack of about 1000 discs piled up
- One to three new discs are added to the base every hour, while old discs slough off at the tip and are phagocytosed by pigment epithelial cells
111
What does the inner segment of photoreceptors contain?
Cell nucleus, Golgi complex and many mitochondria
112
What happens at the proximal end of the photoreceptor?
The photoreceptor expands into bulblike synaptic terminals filled with synaptic vesicles
113
What is the first step in signal transduction in photoreceptors?
- Absorption of light by a photopigment, a coloured protein that undergoes structural changes when it absorbs light, in the outer segment
- Light absorption initiates the events that leads to production of a receptor potential
114
What photopigment is found in rods?
Rhodopsin
115
What photopigments are found in cones?
Three different cone photopigments are present in the retina, one in each type of cone
116
How is colour vision formed?
From different colours of light selectively activating the different cone photopigments
117
Describe opsin:
- Glycoprotein
- Four different types -> one in rods and three in cones
- Small variations in the amino acid sequence of the different opsins permit the rods and cones to absorb different wavelengths of light
118
Describe retinal:
- Vitamin A derivative formed from carotene
| - Light absorbing part of all visual photopigments
119
Describe the response of photoreceptors to light:
- In darkness, retinal has a bent shape (cis-retina) which fits into the opsin portion of the photoreceptor
- When cis-retinal absorbs a photon of light, it straightens out to form trans-retinal
- This process is known as isomerisation -> first step in visual transduction
- After retinal isomerise, several unstable chemical intermediates form and disappear
- These chemical changes lead to production of a receptor potential
- In about a minute, trans-retinal completely separates from opsin
- Final products look colourless (bleaching)
- Retinal isomerase converts trans-retinal to cis-retinal
- Cis-retinal can then bind opsin, reforming a functional photopigment -> regeneration
120
What does the pigmented layer of the retina adjacent to the photoreceptors store?
A large quantity of vitamin A, and contributes to the regeneration process in rods
121
Describe the release of neurotransmitters by photoreceptors:
Absorption of light and insomerisation of retinal initiates chemical changes in the photoreceptor outer segment that leads to production of a receptor potential
122
Describe the release of neurotransmitters by photoreceptors in darkness:
- Sodium ions flow into photoreceptor outer segments through ligand-gated Na+ channels
- Ligand that opens these channels is cyclic GMP (cGMP)
- Inflow of Na+ partially depolarises the photoreceptor
- Membrane potential -> -30 mV
- Much closer to zero than a typical neuron's resting membrane potential of -70 mV
- Partial depolarisation during darkness triggers continual release of NT (glutamate) at the synaptic terminal
- At synapses between rods and some bipolar cells, glutamate is an inhibitory NT
- Triggers postsynaptic potentials that hyperpolarise the bipolar cells and prevent them from sending signals to the ganglion cell
123
Describe the release of neurotransmitters by photoreceptors in light:
- When light strikes the retina and cis-retinal undergoes isomerisation, enzymes are activated which break down cGMP
- cGMP-gated Na+ channels close, Na+ inflow decreases and the membrane potential approaches -70 mV
- Produces a hyperpolarising receptor potential that decreases the release of glutamate
- Dim lights -> small and brief receptor potentials they partially turn off glutamate release
- Brighter lights -> larger and longer receptor potentials that more completely shut down NT release
- Thus, light excites the bipolar cells that synapse with rods by turning off release of an inhibitory NT
- Excited bipolar cells subsequently stimulate the ganglion cells to form action potentials in their axons
124
How do receptor potential travel once they have arisen?
- Receptor potentials arise in the outer segments of rods and cones, and they spread through the inner segments to the synaptic terminals
- NT molecules released by rods and cones induce local graded potentials in both bipolar and horizontal cells
125
What is the importance of convergence, and how does this relate to cone vision?
- Convergence of many rods onto a single bipolar cell increases the light sensitivity of rod vision but slightly blurs the image that is perceived
- Cone vision, although less sensitive, is sharper because of the one-to-one synapses between cones and their bipolar cells
126
What is the function of horizontal cells?
- HCs transmit inhibitory signals to bipolar cells in the areas lateral to excited rods and cones
- This lateral inhibition enhances contrasts in the visual scene between areas of the retina that are strongly stimulates and adjacent areas that are more weakly stimulated
- Horizontal cells also assist in the differentiation of various colours
127
What is the function of amacrine cells?
- ACs, which are excited by bipolar cells, synapse with ganglion cells and transmit information to them that signals a change in the level of illumination of the retina
- When bipolar or amacrine cells transmit excitatory signals to ganglion cells, the GCs become depolarised and initiate nerve impulses
128
Where do axons within the optic nerve pass?
Through the optic chiasm, where some axons cross to the opposite side but others remain uncrossed
129
Where do axons travel after the optic chiasm?
- The axons, now part of the optic tract, enter the brain and most terminate in the lateral geniculate nucleus of the thalamus
- Synapse with neurons whose axons form optic radiations, which project to the primary visual areas in the occipital lobes of the cerebral cortex and visual perception begins
130
Where do some fibres in the optic tracts terminate?
- Superior colliculi: controls extrinsic eye muscles
| - Pretectal nucleus: controls pupillary and accommodation reflexes
131
What is a visual field?
Everything that can be seen by one eye
132
What is the visual field divided into?
Two regions; nasal or central half, and temporal or peripheral half
133
What is the relevance of visual field division?
- For each eye, light rays from an object in the nasal half of the visual field fall on the temporal half of the retina and vice versa
- Visual information from the right half of each visual field is conveyed to the left side of the brain and vice versa
134
Describe the visual field division of axons:
- Axons of all retinal ganglion cells in one eye exit the eyeball at the optic disc and form the optic nerve on that side
- At optic chiasm, axons from the temporal half of each retina do not cross, but continue directly to the lateral geniculate nucleus on the same side
- In contrast, axons from the nasal half of each retina cross the optic chiasm and continue to the opposite thalamus on one side
- Axons of thalamic neurons form the optic radiations as they project from the thalamus to the primary visual field of the cortex on the same side
135
What is retinopathy?
- Involve the small blood vessels of the retina
- Characterised by changes in vessel structure and the development of;
- micro-aneurysms
- neovascularisation
- haemorrhage
- retinal opacities
136
Describe micro-aneurysms:
- Out-pouchings of the retinal vasculature
- Appear as minute, unchanging red dots associated with blood vessels
- Tend to leak plasma, resulting in localised oedema that gives the retina a hazy appearance
- They may also bleed, but areas of haemorrhage and oedema tends to clear spontaneously
- Reduce visual acuity if they encroach on the macula and cause degeneration before they absorbed
137
Describe neovascularisation:
- Involves formation of new blood vessels
- Can develop from the choriocapillaris, extending between the pigment layer and sensory layer, or from the retinal veins, extending between the sensory retina and vitreous cavity and sometimes into the vitreous
- Fragile, leak protein and are likely to bleed
- Cause is uncertain but linked to VEGF
- Hypoxia is the key regulator of VEGF-induced retinal neovascularisation
- Likely that other growth factors and signalling systems are also involved
138
Describe opacities:
- Represent loss of retinal transparency due to haemorrhages, exudates, cotton-wool spots, oedema and tissue proliferation
- Exudates are opacities resulting from inflammatory processes
- Development of exudates often results in the destruction of the underlying retinal pigment and choroid layer
- Cotton-wool patches are retinal opacities with hazy, irregular outlines
- Occur in the nerve fibre layer and contain cell organelles
- Cotton-wool patches are associated with retinal trauma, severe anaemia, papilloedema and diabetic retinopathy
139
What investigations are used to diagnose retinopathy?
- Fundus fluorescein angiogram
- Inject fluorescein IV
- Fluorescein bound to albumin -> remains in normal capillaries
- Use blue flash and yellow filter to see details of retinal circulation
- Optical coherence tomography
- low-powered laser interferometry
- generates detailed cross-sectional image of retina
140
What are the two forms of age-related macular degeneration (AMD)?
Exudative and atrophic
141
Describe exudative AMD:
- New blood vessels growing under retina from choroid
- Rapid
- Metamorphopsia
142
Describe atrophic AMD:
- Atrophy of outer retina
- Slow
- Blurring
143
How does AMD cause blindness?
- Blood vessels and scar tissue grow under retina
- Leaking vessels cause retinal oedema
- Block of O2 and nutrients from choroid
- Eventual scarring causes destruction of photoreceptors
144
Describe the aetiology of AMD:
- Photoreceptors continue to produce photosensitive pigment throughout life
- End of photoreceptor cells decay and are removed by retinal pigment epithelium
- End products accumulate, causing drusen
145
What may up to 30% of AMD cases by attributable to?
Smoking
146
What are some risk factors for AMD?
- Age (rare in people under 70)
- Smoking
- Diet (high doses of vitamin A and C may and zinc may be protective)
- Family history
- Genetics
147
Describe the genetic risk factors for AMD:
- Polymorphisms in complement factor H gene strongly linked to AMD -> regulates inflammation and prevents complement mediated attack on own cells
- 7.4 times more likely to have AMD
- Multiple other genes involved
- complement genes -> CFB, CF1, C2 and C3
- lipids -> genes for HDL and LDL
- ECM -> collagen and matrix metalloproteinase
- Inflammation known to be significant in AMD
148
What is angiogenesis and what are angiogenic stimuli?
- Angiogenesis, which normally accompanies cell proliferation, is the formation of new capillaries from existing small blood vessels
- Angiogenic stimuli, in the context of cell proliferation, include the action of various growth factors and cytokines, in particular VEGF
149
What is the sequence of events in angiogenesis?
- Basement membrane is degraded locally by proteases
- Endothelial cells migrate out, forming a sprout
- Endothelial cells following the leading cells proliferate under the influence of VEGF
- Matrix is laid around the new capillary
150
What is ranibizumab?
- A monoclonal antibody fragment that binds to VEGF, given via intravitreal injection by opthamologists
- Repeated monthly for three doses and then as required
151
What are the effects of ranibizumab?
- 96.4% lose <15 letters
- 40.3% improved by 15+ letters
- 38.6% 6/12 or better
- 15.4% 6/60 or worse
152
Describe the IVAN trial:
- Compared bevacizumab (£49/dose) to ranibizumab
- Compared monthly injections to "as required" injections
- No difference between ranibizumab and bevaciumab at 12 months
- No difference between monthly and as required injections
