Applied Anatomy of the Eye Flashcards
1
Q
What is the role of the vestibular nuclei in the visual system?
A
Gaze stabilisation
2
Q
What is the role of the occipital lobe regarding vision?
A
Pursuit eye movements
Accomodation
3
Q
What is the role of the frontal lobe regarding vision?
A
Voluntary eye movements
Also helps control voluntary body movements
4
Q
What is the function of the cornea?
A
Refraction of light
5
Q
What is the function of the lens?
A
Focusing light - aim for the macula/fovea - this is refraction
Accommodation reflex
Fine focus of visions
6
Q
What is the function of the iris?
A
Controls the amount of light entering the eye.
7
Q
What makes up the structure of the Cornea?
A
The outer epithelial layer
Bowmans layer (anterior limiting lamina) - acellular collagen fibres
Stroma - keratocytes (specialised fibroblasts)
Descement membrane (posterior limiting lamina) - basement membrane for corneal endothelium
Endothelium.
8
Q
What are the key features of the corneal epithelium?
A
Several layers of cells
Barrier to water and bacteria entering the cornea
Maintains a smooth optical surface for refraction
Is constantly replaced/regenerated.
9
Q
What are the key features and function of the corneal endothelium?
A
Single layer of hexagonal cells
Allows transport of nutrients including glucose into the cornea
Pumps water out to maintain clarity of stroma
Never replaced
10
Q
What does emmetropia mean?
A
Normal refraction of light by the cornea onto the lens.
11
Q
What is hypermetropia and how should it be corrected?
A
Long sighted
Light is refracted from the cornea too far back behind the retina
Fixed with converging/convex contact lenses.
12
Q
What is myopia and how should it be treated?
A
Short sightedness
Refraction error - cornea refracts light too far forward, does not hit retina
Fixed with concave/diverging lenses.
13
Q
What is astigmatism of the eye?
How is this corrected?
A
When the eye is not spherical in shape, rather is more rugby ball shaped aka curvature is steaper in the vertical compared to the horizontal axis
is corrected using cylindrical lens with different powers.
14
Q
What are some common pathologies of the cornea?
A
Corneal ulcer
Corneal dystrophy
Keratoconus
Corneal odema
Corneal graft
15
Q
What is a corneal ulcer?
A
An open sore in the outer layer of the cornea.
Can occur due to scratches on eye surface, severely dry eyes, complication of incorrect use/hygiene with contact lenses
Commonly become infected typically by Pseudomonas aeruginosa.
Can perforate
Vision is reduced.
16
Q
What is the common treatment for a corneal ulcer?
A
Start treatment as soon as possible
Often requires two days of topical antibiotics (eye drops) every 30 mins.
17
Q
What is corneal dystrophy?
A
A group of genetic disorders often progressice in which abnormal material often accumulates in the cornea.
Can lead to visual impairement
18
Q
What is keratoconus?
A
The cornea thins and gradually buldges outwards and downwards in a cone shape
Can cause blurry and distorted vision.
19
Q
What is corneal oedema?
A
Appears as a cloudy eye
Swelling in cornea after injury or infection
May be associated with degneration of epithelial cells
20
Q
What is a corneal graft?
A
Corneal transplantation where damaged tissue is removed and placed with a donated corneal tissue
21
Q
What initiates the change in the lens during accommodation?
A
Circumferential ciliary muscles contract and relaxes to alter the tension of the lens capsule allowing lens to change shape.
Contraction - less tension of suspensory ligament of lens - becomes shorter and wider (more convex) - refract light closer - focus on short distance.
22
Q
What is a common pathology of the lens?
A
Cataract formation - causes progressive opaque eye lens, reduces light entering the eye hence reducing visual acuity.
Normally affect lens nucleus - associated with aging and denaturation of proteins in the lens.
Can be treated surgically.
23
Q
What is the anatomy of the lens of the eye?
A
Epithelial differentiated organ - elastic, transparent and biconvex in shape
Consits of lens capsule, lens epithelium (stable functioning and production of lifelong lens fibres), lens fibres and the zonules.
Fibres cells make up the lens nucleus.
24
Q
What are some risk factors for cataract formation?
A
Age
Diabetes
Corticosteroids
Congenital
Trauma to the eye
25
What are the ten different layers of the retina?
Nerve fibre layer
Ganglion cell layer
Inner plexiform layer
Inner nuclear layer
Outer plexiform layer
Extrenal limiting membrane
Inner segment of photoreceptors
IS/OS junction
Outer segment of photoreceptors
Retinal pigment epithelium
Bruchs membrane
Choroid.
26
What is the simplification of the different layers in the retina?
Nerve fibre layer
Ganglion cells
Bipolar cells
Photoreceptors
Retinal pigment epithelium
Choroid (blood supply)
27
What is the structural difference at the fovea?
Highest concentration of cones
Nerve fibre layer, ganglion cells and inner nuclear layer are deviating away from the fovea, allow light to hit directly onto photoreceptors - higher level of visual acuity.
28
What type of vision are rods responsible for?
Scotopic vision - under low light conditions
29
What type of vision of cones responsible for?
Phototopic vision - in high light intensities
30
What is the arrangement of opsin in cones cells?
Iodopsin is found in cones
3 different opsins present in all cones, but one predominates in each - each type of opsin is sensitive to a different wavelength of light, enables to differentiate between different colours
Red, green, blue in order of descending wavelength
31
What is the different micro structure of rods/cones?
Each consist of an outer segment, inner segment and a synaptic terminal.
The inner segment contains a nucleus, endoplasmic reticulum and mitochondria in both.
The outer segment contains a disks and plasma membrane in rods, cones only have plasma membrane.
The inner and outer segments are connected by a connecting cilium.
32
What is the distribution of photoreceptors on the retina like?
No photorecepotrs at the optic disk
Cones - highest concentration at the fovea, decrease in concentration as you spread outwards
Rods - none at fovea, highest concentration just outside fovea then decrease at outwards, are widely spread throughout the retina
There are significantly more rod than cones in the retina.
33
What is the role of the retina pigment epithelium in phototransduction?
Stores vitamin A
Production nd recycling of photo-pigments
Phagocytoses old discs
34
What is the role of recoverin in phototransduction?
Provides adaptation to high light environments
Recoverin is a calcium dependent inhibitor of rhodopsin kinase, which turns off phosphodiesterase
Hence more light, less Calcium, recoverin is less active, rhosopsin kinase not inhibited, PD is inhibited, regulate on signalling.
35
What is the role of amacrine cells in phototransduction?
Amacrine cells are inhibitory cells in the retina
They receive signals from bipolar cells and regulate activity of bipolar and ganglion cells.
Provide negative feedback
36
What is the process of lateral inhibition in phototransduction?
Mediated by horizontal cells
Light in central PR - hyperpolarised - less glutamter - reduced activation of horizontal cells - reduced inhibition on neighbouring PR - more depolarisation of surrounding PR - perceive dark
Same vice versa
Enhanced the central signal by increasing contrast with surroundings.
37
What are some common pathologies of the retina?
Colour blindness
Retinal vascular occlusion
Diabetes
Macular Degeneration
Retinal Detachment.
38
What are the different types of colour blindness?
Prot - red cones (L)
Deuter - green cones (M)
Trit - blue cones (S)
Anomaly - malfunctioning
Anopia - absent
Deuteranomaly is the most common (5% of pop), followed by protanomly, protanopia, deutranopia (1% pop each).
39
How do we test for colour vision?
Use Ishihara plates
40
What is the process of central retinal artery occlusion?
Loss of blood supply to the retina (not the optic nerve).
Retina thins as cells die.
Opthalmogic emergency, presents with sudden, paniless, monocular vision loss over seconds. Often have a history of atherosclerotic disease.
41
What pathology is shown on the image?
Central retinal artery occlusion
Pallor of the infected retina
Central cherry red spot - due to odema in the fovea, causes to retain is normal colour
42
What is central retinal vein occlusion?
Venous thrombosis leading to haemorrhage, oedema, cotton wool spots and neovascularization on the retina.
Blood vessels in the back or the retina may leak or the retina may become ischemic.
43
What pathology is shown on the fundoscopy exam?
Central Retinal Vein Occlusion
Haemorrhages
Oedema
Cotton wool spots
Neovascularisation.
44
What happens in diabetic retinopathy?
Microvascular leakage, occlusion and microaneurysm lead to oedema, exudation and haemorrhage in the inner retinal layers.
Ischemia leads to neovascularization.
Damage mediators by hyperglycemia and hypertension.
45
What pathology is shown on this fundoscopy?
Diabetic retinopathy
Microvascular leakage, odema, exudation (cotton wool spots), Flame shaped haemorrhage and dot and spot haemorrhage, neovascularization.
Microaneurysms
46
What is dry age related Macular Degeneration?
A slow deterioration of the cells of the macula, retinal cells die and are often not renewed due to ischemia.
Build up of waste products from photoransduction.
May lead to atrophic changes and detachment of the retina from the choroid in the region of the macula.
Caused by drusen (fatty deposits) separating the retinal pigmented hence neural layer from the choroid beneath.
47
What pathology is shown on the fundoscopy?
Drusn accumulation (small yellowish depostis)
May also show geographic atrophy
48
What is wet age related macular degeneration?
Is a development from dry AMD.
Inflammation and hypoxia leads to choroidal neovascularisatoin, which breaks through the outer retinal layers causing oedema and haemorrhage.
Causes distorted vision as PR are displaced
49
What pathology is shown on the fundoscopy?
Retinal odema and localised elevation
Detachment of retinal pigment epithelium
A gray- green discolouration under the macula
Exudates in and around the macula
Subretinal haemorrhage
50
Why do you get vision distoration with wet ARMD?
Each cone is responsible for seeing one part of the visual field, that is mapped exactly in the occipital cortex
Id odeme seperates/moves cones around they will detect slightly different area in the external environment
THe brain will still assemble the images as if in correct original position - results in a distorted image.
51
What is retinal detachment?
Posterior vitreous detachment from the retina
PVD extends but vitresous remains attached to retina, so creates a tear in the retina.
Fluid can accumulate behind the tear in the retine (between retina and choroid)
Fluid continues to accumulate - results in retinal detachment.
Requires immediate treatment
52
What pathology is shown on the fundoscopy?
Retinal detachement
53
What are the different pathologies in the eye can prevent vision?
Corneal opacity - infection, odema or dystrophy
Cataract formation in the lens
Retinal problems - CRAO, CRVO, retinal detachment, wet ARMD, diabetic retinopathy.
54
What is the blood supply to the optic nerve?
Supplies by the posterior ciliary arteries - these travel on the outer surface of the optic nerve and eventually contribute to the choroid to supply the retina and optic nerve.
The central retinl artery passes through the centre of the optic nerve but does NOT supply the optic nerve.
55
What are some common problems with the optic nerve?
Inflammation - optic neuritis
Glaucoma
Ischaemia
Compression
Papilloedema (swelling of optic nerve)
56
How can optic nerve problems present?
Reduced visual acuity
Altered colour vision
Visual Field defect
Relative Afferent Pupil Defect.
57
What is the basic idea of optic neuritis?
Inflammation of the optic nerve.
Can result in variable visual loss, including colour vision problems but usually recovers within a few months.
Can be related to MS (50%) or be post viral .
Over time the optic nerve develops pallor on fundoscopy.
58
What is glaucoma?
Progressive optic neuropahty causing a loss of nerve fibre layer, causing cupped optic disc appearance and corresponding visual field defects.
Commonly associated with raised intraocular pressure due to unbalance drainage and production of aqueous humour.
59
What is optic disk cupping?
Degeneration of the optic nerve - results in a thinner outer layer and relatively larger inner layer for vessel passage.
Will have a cup to disk ratio greater than 0.5.
60
What is anterior ischaemic optic neuropathy?
What does it look like on fundoscopy?
Most commonly due to microvascular occlusion related to diabetes, hypertension and atherosclerotic disease, but can be due to inflammatory causes including giant cell arteries.
Occlusion of the posterior ciliary arteries.
Presents on fundoscopy as a chalky- white allow of the optic disk with edema.
61
What conditions can cause optic nerve compression?
Inflammatory conditions such as thyroid eye disease
infection such as orbital cellulitis
Haemorrhage
Tumours.
62
What is papiloedema?
Optic disk swelling with rasied ICP, usually bilateral and vision in minimally disturbed.
Optic nerve is surrounded by sheath containing CSF in continuity with subarachnoid space, increase ICP reduces axoplasmic flow, cause venous stasis, fluid accumulation, and haemorrhage, optic nerve will swell.
63
How does papilloedema present?
Early stages have no visual loss
Later an increased blind spot may occur
Followed by an increasing peripheral field loss
Patient may be aware of visual obstructions
64
What pathology is shown on this fundoscopy?
Papilloedema
65
What is the neural circuitry for pupillary constriction?
Light detected on retina, action potential generated and electrical information patterns are passed down optic nerve through chiasm then down the optic tract (in both left and right as light on temporal and nasal retina)
Now two identical pathways as follows on either side of the brain:
Optic tract projects to and synapses in ipsilateral pre-tectal nucleus in the midbrain.
Projects and synapses bilaterally in the Edinger Westphal Nucleus, containing parasympathetic efferents of the CN3.
Projects to and synapses in the ciliary ganglion
Short ciliary nerves project to the sphincter pupillae muscle release ACh, causing constriction of the pupil.
66
What is the neural circuitry for pupillary dilation?
Originating in the hypothalamus sympathetic fibres descend through the ipsilateral brain stem and into the spinal cord where they syanpse in the lateral horn.
The second-order neurons pass out in the roots of C8 and T1, enter the sympathetic chain ganglion, and ascends to synapse in the superior cervical ganglion.
This gives rise to postganglionic fibres which ascend the wall of the internal carotid artery to the cranial.
Pass directly through the ciliary ganglion to the iris as the long ciliary nerve. NA release causes contraction of the dilator pupillae muscle dilating the pupil.
67
What is the effect of pilocarpine on the pupil?
Cholingeric agonist
Contraction of pupil
Miosis
68
What different drugs can dilate the pupil?
Phenylephrine - alpha 1 agonists (dilates)
Tropicamide, cylocepntolate, atropine - muscarininc antagonists
69
What is the neural circuitry underpinning the accommodation reflex?
A - constriction of the pupil - optic nerve - primary visual cortex - frontal eye fields - bilateral EW - cilliary ganglion - short ciliary nerve - sphincter pupillae
B - lens accomodation - same as above - short ciliary nerve to ciliary muscles contraction - zonules and elastic capsule of lens relax, becomes more spherical in shape - focuses on close distances
C- convergence on a nearby object - frontal eye fields to motor components of oculomotor nerve nuclei - contraction of medial rectus.
**
70
What is meant by a PERLA pupil response?
Pupils are equal
Reactive to light
71
What is light near dissociation?
If a pupil responds to light it will respond to accommodation.
If there is no response to light however there may still be accommodation.
Often due to a problem in the afferent pathway***
72
What is meant by physiological abnormal pupils?
When pupils are unequal in size but have an equal construction to light and near reaction
This is normal and seen in around 20% of the population.
73
What is Marcus Gunn pupil? RAPD
Norm equal in size
When pupils are unequal in size during light reaction
Dilates to direct light and constriction to indirect in swinging light test.
Near reaction is as light
Caused by optic nerve pathology.
74
What is Holmes Adie pupil?
Pupils are dilated
Show minimal constriction to light and some constriction in the near reaction
Thourght to be due to ciliary ganglion damage - often viral in cause.
75
What is an Argyll-Robertson Pupil?
When pupils are bilateral irregular and small.
No light reaction
Constriction in the near reaction
Caused by syphilis.
Thought to cause damage between the pretectal and EW nucleus.
76
What is Horners pupil?
Damage to the SANS to the eye
Results in abnormally constricted pupils (miosis)
Pupils will remain contracted during the light and near reaction. (norm response must look for absence of change)
Present with sympathetic chain damage; ipsilateral ptosis and anhydrosis.
77
What is a third nerve palsy pupil?
When the pupil is abnormally big.
Caused by damage to the oculomotor nerve including its PANS components within the EW nucleus
No response to light, no response to near reaction
Also presents with ptosis and an eye deviated down and out.
78
What drugs can constrict the pupil?
Pilocarpine - muscarinic agonist
Opiods - activation of the PANS.
79
What structure co-ordinates the contraction of different muscles in the eye?
The superior colliculus.
80
How does the vestibular nuclei stabilise gait?
1. head motion is detected by vestibular apparatus (often side turning head towards)
2. Projects from vestibulocochlear nerve to to the vestibular nuclei in the brainstem
3. Projects to contralateral abducens nucleus - cause lateral rectus contraction
4. Abduces projects to contrlateral oculomotor nucleus - cause medial rectus contraction
81
What is the purpose of the ventral stream in the visual system?
Is a visual association pathway located in the inferior temporal cortex
Associated with recognition of objects and people etc
82
What is the purpose of the dorsal stream in the visual system?
Is a visual association pathway located in the parietal lobe.
Responsible for movement and positional information.
83
What is the role of the frontal lobe in vision?
Provides unconscious visions
Role in blindsight ?? (brainstem response to light projection to the frontal cortex)
Role in voluntary eye movements and body movements
Frontal eye fields - role in saccadic movements via connections to the gaze centres. ??
84
What are the main different causes of pain in the eye?
Foreign body
Trauma
Reduced tear film
Corneal epithelial disruption
Inflammation
Raised IOP
85
What is the sensory innervation to different elements of the eye?
Provides via the trigeminal nerve
The opthalmic division - upper eye lid, palpebral conjunctiva, bulbar conjunctiva, cornea, ciliary body and iris
The maxillary division - lower eyelid and palpebral conjunctiva.
No pain receptors in lens or retina
86
How does sudden raised intra-ocular pressure cause pain?
Activation of nociceptors by ATP.
87
What are the different types of stimuli corresponding to pain receptors in the eye?
Noxious mechanical forces - mechanorecepotrs
Heat, exogneous irriatns, endogenous inflammaion - polymodal receptors
Dryness, temperature changes - cold receptors.
88
What is keratitis?
Inflammation of the cornea
89
What is meibomianitis?
Inflammation of the meibomian gland
Sebaceous gland in eyelid secretes fluid to make up tear film
90
What is blepharitis?
Inflammation of the eye lid.
91
What ee structures should always be checked during an eye examination?
Eyelids
Conjunctiva
Cornea
Anterior chamber
Iris.
92
What is the basic advice for blepharitis and melbomianitis?
Inflammation of the eyelids/meibomain glands
Very common
Multiple different types
Treat with a warm compress
And lid hygiene.
93
What are some common lumps/bumpb that can be found on the eye?
Cyst of moll - blocked gland of moll - modified sweat gland
Stye - blocked sebaceous gland related to lash follicle infection
Chalazion - blocked meibomian gland -
94
What are some different diseases of the eye lid?
Entropion - eyelid turned in - lashes rubbing on cornea, lashes and lid are inverted.
Ectropion - eyelid turned out
Trichiasis - lashes turned in and rubbing on cornea (grow inwards towards eye), but lid position is normal
Both caused by orbital fat shrinkage.
95
What are the emergency lid diseases?
Entropion
Trichiasis
Damage to cornea risk
96
What are some common diseases of the conjunctiva?
Bacterial conjunctivitis - sticky discharge
Viral conjucntivis - water discharge, affects follicles
Allergic conjunctivitis - chemosis and papillary changes. (swollen with little bumps)
Pupils and vision tends to be normal
97
What are the two most common categories of foreign bodies in the eye by anatomy?
Subtastal foreign body - under eyelid
Corneal foreign bosy.
98
What are some common corneal problems?
Dry eyes
Corneal abrasion - inflamed conjunctiva and epithelial defect, pupila and vision is normal
Dendritic ulcer
99
How can we view corneal lesions on examination>
Flourescein and blue right to show epithelial defect.
100
What is bacterial keratitis?
How should you treat it?
Central ulcer of the cornea, round, white and greater than 1, with possible uveitis.
Mostly in contact lense wearers with poor contact hygiene
Requires urgent corneal scrape and gram stain for microbe identification.
Admit, adminster intensive antibiotics, cycloplegia and later steroids
Topical eye drops eye 30mins for 2 days
Antibiotics include - levofloxacin, ofloxacin, cefuroxime, gentamicin.
101
How does acute angle closure glaucoma present?
Severe pain - ATP mediated
Vomiting
Reduced Vision
Rainbow haloes
Injected conjunctiva - enlarged bv
Shallow AC
Mid dilated pupil
102
How does hypermetropia relate to glaucoma?
Long sight-smaller eyes
Shallower AC
Enlarged lens
Pupils dilate in low light
Iris sticks to enlarged lens
Aqeous fluid cannot flow into AC, pushes iris forward
Irisi closes off already narrowd angle
IOP rises.
103
What is a YAG iridotomy?
Powerful beam of light is used to make holes in the iris
This increases the flow of fluid through the iris, helps increased drainage into the trabecular meshwork and decrease IOP.
104
What is uveitis?
What causes it?
Inflammation of the iris, choroid and ciliary body - can be one or more than one.
Typically presents with circumcillary redness, white cells in the anterior chamber and posterior synechiae.
Can be related to other systemic inflammatory diseases, autoimmune disease or be idiopathic.
Treatment includes steroids.
105
What is endophthalmitis?
An emergency - infection of the anterior and posterior chambers of the eye.
Significant pain, redness and reduced vision.
Requires urgent admission and vitreous tap.
Treat with antibiotics intravitreal vancomycin, ceftazidime +/- dexamethasone.
'Golden hour for treatment' or risk of permanent blindness
Can occur post surgery, or after trauma.
106
What is iritis?
Inflammation of the iris
Cornea - keratic precipitates
Anterior chamber - white cells present
Pupil can be stuck down
IOP norm or raised
Vision is reduced
