Eyes Flashcards
How do images form on the retina?
Light waves from object bent by cornea + lens (refraction of light)
Closer the object thicker the lens
How does the eye accommodate for distances?
Ie (from distant to close)
Lens changes shape
>(thicker + more spherical )
Pupils constrict
Eyes converge
How does the lens change shape?
Ciliary muscle contracts making ciliary body bulge
Space in middle decreases
Suspensory ligaments become lax
Lens no longer stretched, becomes thicker
Opposite if close to distant (muscle relaxes etc)
What effect do the pupils changing dilation have in accommodation?
By constricting allows only the rays from the object into the eye, or allows more rays in if dilate Pupillary constrictor (sphincter pupillae) is a concentric muscle around the border of the pupil which gets parasympathetic innervation.
What are the types of refractive errors?
Myopia
Hyeropia
Astigmatism
Presbyopia
What is myopia?
Short sightedness
Where image is formed in front of the retina
Eyeball often too long
Bending power too much for the eye
When object brought closer, rays are divergent and need to be bent more, thus formed on the retina
What are the symptoms of myopia in children?
Headaches, unable to see whiteboard
Can form divergent squint
Toddlers may lose interest in sports/people - more interest in books/pictures
How do you correct myopia?
Bending power must be decreased
Bi-concave lenses - spectackes/contact lenses
Laser surgery
What is hyperopia?
Long-sightedness
Bending power not great enough, image formed behind retina
Eyeball often too short, cannot see nearby
Uses muscles to thicken lens for far away objects
Cannot thicken past a point, and then cannot see clearly
What are teh symptoms of hyperopia?
Often eyestrain when reading/on computer
Convergent squint in children - needs immediate correction
May have lazy eye
How do you correct hyperopia?
Can treat with biconvex lenses/glasses
+ surgery
What is astigmatism?
Surface has different curvatures
Therefore bending of light never the same as in the other axis so image hazy
Laser eye surgery, or lenses only curved in one axis
>Special contact lenses called toric lenses
What is presbyopia?
Where lens gets less mobile/elastic
Not as able to change shape, so nearby objects difficult
Treat with biconvex glasses
What is phototransduction?
Conversion of light energy into electrochemical response by photoreceptors (rods/cones)
Phototransduced rods/cones activate optic neurones (generate AP)
Photoreceptors (contained in lamellae part of rod/cone) have different wavelengths
Send signals when specific sensitivity reached
What pigment is responsible for vision?
Opsin + 11-cis Retinal
What is 11-cis retinal?
chromophore nesting in the opsin - formed from dietary Vitamin-A.
When light falls on 11-cis retinal, isomerises into transretinal - elongates and won’t fit into opsin, so rhodopsin splits resulting in bleaching of visual purple
What is the phototransduction cascade?
Rhodopsin is activated
Leads to sodium channels closing
Relative hyperpolarisation of photoreceptor cell
Transmitted by a flux of calcium ions, ultimately stimulates retinal cell
How is rhodopsin regenerated?
Trans retinol converted to 11-cis rol, converted to 11-cis retinal
Bi product of retinyl esters, and so need continous vitamin A in diet
Why is vitamin A important?
Without can lead to night blindness
Conjunctiva and corneal epithelium abnormal as needed for epithelium health
Clinical sign - bitots spots in conjunctiva - triangle of spec. Last a while
Corneal ulceration - dye to see extent
Cornea can “melt” leading to future opacification
What are the two types of ocular musclee + their function?
Intrinsic muscles - help control pupil diameter + alter lens curvature
Extrinsic - move eye
Where do the extrinsic muscles arise from?
Recti - from apex of orbit from annular ring
Superior oblique - posterior roof of orbit
Inferior oblique - anterior floor of orbit
What are the attachments of the levator papellae superiosus?
Roof of orbit
To upper eyelid
What are the attachments of the recti muscles?
Tendonous ring
Sclera anteriorly
What are the attachments of the superior oblique?
Lesser wing of sphenoid Sclera posterioly (via trochlea)
What are the attachments of the inferior oblique?
Medial part of orbit floor
Sclera posteriorly
Why do the extrinsic muscles move the eye in multiple directions?
Muscles attached along orbital axis, not optical so pull eyeball at an angle - each muscle will have more than one movement
Oblique muscles attached to posterior part of sclera, so pull anterior part in opposite direction
What are the signs of the three main eye nerve palsies?
Third >Drooping eyelid >Eye can move only laterally (and slightly down) Fourth >Eye moving up when adducted Sixth >Eye being adducted >Unable to abduct
What is squint?
Misalignment of the eyes
Leads to two different images in brain
What are the two main types of squint?
Esotropia - manifest convergent squint
Exotropia - manifest divergent squint
What are the consequences of squint?
Amblyopia (lazy eye) - brain supresses images from one eye leading to poor vision in that eye without any pathology.
Treat by stimulating “lazy” eye to work with eye patch in younger years
Diplopia (double vision) - normally squint due to palsies
What is the visual pathway?
All fibres from eye pass through optic chiasma. The Temporal view (fibres near nasal) cross over to other side of the brain
Therefore two optic tracts formed, one from right, one from left visual fields, and are on opposite side of brain to their field
These fibres synapse at the lateral geniculate body of thalamus
Form optic radiation, passes behind internal capsule to reach primary visual cortex in occipital lobe
Thus the Right visual cortex sees the left half of the visual field and vice versa.
What visual defect would damage in the optic nerve lead to?
Blindness in one eye
What visual defect would damage in the middle of the optic chiasma lead to?
Both lateral view lost (bitemportal hemianopia)
What visual defect would damage in the optic tract lead to?
contralateral homonymous hemianopia
Blindness in both the right or the left field of visions in both eyes
How do you elicit the pupillary reflex?
Start in dimly lit room
Pen torch in one eye, check that both pupils constrict
Swing light to other side, both should remain constricted
What are the intrinisc eye muscles?
Ciliaris muscle in ciliary body
Constrictor pupillae in iris at pupillary border
Above innervated by parasympathetic CN III
Dilator pupillae radially running muscle in iris
Sympathetic innervation
Why does the pupillary response affect both eyes?
Impulses travel along optic nerve - optic chiasma - tract when light hits retina
Some fibres do not enter the lateral geniculate body of thalmus
Instead enter midbrain (where CN III is situated)
Part of the IIIn nucleus is the edinger-westphal nucleus for these parasympathetic
They go to the EWN on both sides, thus initiating response on each side
How does the pupillary response affect both eyes from the EWN?
Preganglionic parasympathetic fibres from EWN pass through IIIn into orbit
Go to synapse in ciliary ganglion
Postganglionic fibres go through short ciliary nerves to constrictor pupillae
Constriction of both sides
What are the main pupil abnormalities?
Different sizes - anisocoria
Pupils may react abnormally to light
What is horner’s syndrome?
Anisocoria due to damage to the sympathetic innervation to the pupil.
You might also see ptosis (drooping of the eyelid) on the affected side
Other signs – anhidrosis (loss of sweating on the affected side)
Horner’s syndrome can occur due to disruption of sympathetic fibres at any point. An example would be Pancoast’s tumour of the lungs!
What can cause pupils to react abnormally to light?
Any abnormality of the afferent/efferent limb/ centre of reflex
Diseases of the retina –
> detachment/ degenerations or dystrophies
Diseases of the optic nerve – such as in optic neuritis (frequently seen in MS)
Diseases of the III cranial nerve (efferent limb)
What is a cataract and how common is it?
Lens opacification
~30% >65
Initially looks like spokes, then just becomes white
Why do cataracts develop?
UV rays enter eye, lens absorbs to stop harm to retina
Lens damaged in process
Older fibres never shed/regenerated
Damaged lens fibres go opaque, cause cataract
How do you treat cataract?
Surgery only way
Small insicion + lens capsule opened
Cataractous lens removed by emulsification (pharmacoemulsification)
Plastic lens placed in its stead
Lens implant after cataract surgery – PCIOL = Posterior Chamber Intra Ocular Lens
What is glaucoma?
Raised intraocular pressure
2nd most common cuase of blindness
Most commonly seen form of primary glaucoma is Primary Open Angle Glaucoma (POAG)
~1% population aged 40 – 89
Bilateral
Patient can be asymptomatic for a long period of time
Picked up on routine eye exams
What are the consequences of a raised IOP?
Pressure on nerve fibres cause them to die out and results in reduced visual field
Optic disc appears pale, unhealthy and cupped
Ultimately results in blindness
How do you treat primary open angle glaucoma?
Eye drops to reduced IOP Beta blockers Carbonic anhydrase inhibitors Prostaglandin analogues Laser trabeculopasty Trabeculectomy surgery
What is angle closure glaucoma?
Sudden onset and painful, with vision loss/blurring + headaches On examination >Red eye, cornea often o paque >Pupil mid-dilated >IOP severely raised
How does the angle close?
1 Functional block in the small eye - lens enlargement
2 mid dilated pupil - periphery of iris crowds around angle and outflow is obstructed
3 iris sticks to pupillary border prevents reaching anterior chamber. Leads to iris ballooning anteriorly and obstructing angle
How do you treat acute episodes of raised IOP?
Decrease IOP
>IV infusion w/ or w/o oral therapy - carbonic anhydrase inhibitors
Analgesic
Constricor eye drops
Steroid eye drops
Iridotomy (laser) both eyes to bypass blockage
What is the difference between open and closed angle glaucoma?
In open angle the drainage through the tracbecular meshwork is blocked
Which leads to GRADUAL increase in IOP
Closed angle is where iris blocks angle so AH cannot drain
Which leads to SUDDEN increase in IOP
Red eye + pain
Emergency
What are the types of corneal ulcer
Infectious - needs aggressive management to prevent spread/scarring
Viral, bacterial, fungal
Non-infectious - uclers due to trauma, corneal degeneration or dystropy
What are is a corneal dystrophies, how do they present?
Group of disesases that are >Bilateral, opacifying, non-inflammatory >Mostly genetic >Sometimes accumulation of substances Present in first-fourth decade Decreased vision One layer of cornea - spread to others
What is stromal corneal dystrophy?
Lattice (stromal)
Autosomal dominant
Depositation of amyloid material in corneal stroma
Patient presents with eye irritation, pain, blurred vision
Examination shows bilateral criss-crossing opacities in corneal stroma
Treat by managing symptoms, corneal transplant
What is Fuch’s endothelial corneal dystrophy?
Asymmetrical bilateral progressive odema of cornea
Elderly
Destruction/death of epithelium cells
Eventually opacification
Initially symptomatic, later corneal transplant
What are teh types of uveitits?
Anterior
Intermediate
Posterior
What is anterior uveitis?
iris inflammed - w/ or w/o ciliary body
Leaks plasma and white blood cells into aqueous humour
Seen in slit lamp examination as hazy anterior chamber + cells deposited in back of cornea
Red, painful eye w/ vision loss
What is intermediate uveitis?
cilliary body inflammed
Ciliary body inflammed leaks cells + proteins
Leads to hazy vitreous humour
Floaters/hazy vision
What is posterior uveitis?
choroid inflammed
Frequently spreads to retina, causing blurred vision
What are the causes of uveitis?
Isolated illness
Non-infections auroimmune disease
Infectious causes
Systemic disease
What is conjunctivitis?
Self limiting bacterial/viral infection of conjunctiva
Red, watery eyes, increased discharge
No loss of vision as long as infection does not spread to cornea
Treat with antibiotic eye drops if bacterial
What is fluroescein angiography?
To test if blood vessels getting enough blood flow
Can point to macular degeneration or diabetic retinopathy
Eye drops to dilate eyes
Take pictures of inner eye
Then inject fluorescein dye into vein in arm
Take pictures as fluroescein moves through eye
What is optical choerance topography?
Non-invasive imaging test using light waves to take cross sections of retina
What can cause sudden painless loss of vision?
Central retinal vein occlusion Central retinal artery occlusion Ischaemic optic neuropathy Stroke Vitreous haemorrhage Retinal detachment Sudden discovery of pre-exisiting unilateral LoV
What are teh common causes of central retinal vein occlusion?
Hypertension
Glaucoma
Hyperviscosity
Inflammation
What are the common causes of central retinal artery occlusion?
Embolis
Inflammation
What are the clinical features of ischaemic optic neuropathy?
Pain on eye movements Reduced vision Red desaturation Central scotoma Relative afferent pupil defect Swollen optic disc
What can cause a gradual painless loss of vision?
Cataract Refractive error Age-related macular degeneration Open angle glaucoma Diabetic retinopathy Hypertensive retinopathy Inherited retinal dystrophies Drug-induced retinopathy
What are age-related macular degeneration and its risk factors?
Common (10% >65, 30% >75) Progressive loss of central vision Risk factors >Age >Smoking >Poor diet
How does diabetic neuropathy present?
Cotton wool spots + exudates visible on retina
Vascular abnormalities
Maculopathy
What is cone dystrophy?
Inheritance
Sporadic (90%)
Dominant, X-linked recessive
Photopic ERG reduced, scotopic normal
What drugs can induce a retinal dystrophy?
Anti-malarials
Phenothiazines
Tamoxifen
What are retinal dystophies?
Series of inherited conditions affecting photoreceptor functions leading to progressive loss of vision
How do you treat uveitis?
Treat infection if present
Topical anti inflammatory
Systemic steroid
Systemic immunosuppresants
What are the features of orbital cellulitis?
Pain, redness, lid swelling Systemically unwell Double vision/limitation in EOEM Conjunctivitis/chemosis Exophthalmos Blurred vision
What are teh common causes of orbital cellulitis?
Sinusitis / dental infections
Haematological spread
What are the types of adnexal oncology?
Eyelid tumours
Lacrimal drainage tumours
Orbital tumours
How does squamous cell papilloma (of eye) present?
Pedunculated or sessile (broad-based)
Characteristic ‘raspberry’ texture
How does basal cell papilloma (of eye) present?
= Seborrhoeic keratosis Greasy, brown, flat, round/oval Similar texture to squamous cell papilloma ‘Stuck on’ appearance Unrelated to sun exposure
What is melanocytic naevus?
Composed of atypical melanocytes
Location of these melanocytes influences clinical appearance and potential for malignant transformation
What is pyogenic granuloma?
Fast growing, highly vascularised granuloma
May follow surgery, infection, trauma
Erythematous pedunculated mass
Rx Excision
What is basal cell carcinoma of eye?
Features suggestive of BCC Slow, inexorable growth over months Usually non-pigmented, elevated, ulcerated Pearly, rolled, irregular border Telangiectasia Lack of tenderness
What is squamous cell carcinoma of the eye?
Sun damaged skin and pre-existing AK
Scaly surface over a thick plaque
Growth over weeks rather than months
Metastatic risk of 3-10%
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