week 1 instant anatomy tutorial (high yield facts) Flashcards
what is the function of the meibonian glands(tarsal glands)?
secrete lipids to preserve tears
what is ptosis
dropping of eyelid down/too low
what controls eye opening?
levator with Muller’s muscle
[Levator is controlled by the CNIII; Muller’s muscle is under sympathetic control]
what controls eye closing?
orbicularis oculi
[Controlled by
the CN 7th nerve]
muller’s muscle is innervated by what?
sympathetic innervation - fright and eyes go big (let in light)
what are the signs of Horner’s syndrome (compromised sympathetics)
ptosis, miosis, anhydrosis, red/flushing
where/what is the orbital septum?
lies just posterior to the orbicularis oculi muscle.
fibrous band to protect against infection becoming deep (and going to brain)
what us the difference between orbital and preseptal cellulitis?
Orbital cellulitis is an inflammation posterior to the septum and is sight threatening. (opposite = preseptal cellulitis) - kids usually admitted to be on the safe side
infected eye cause by what? how to distinguish between the two causes
eyelid infection going backward or sinus infection coming forward.
nose problem and round rim of eye = sinus; extensive eye and face = eyelid
the orbicularis oculi two parts and functions
The orbital part of the orbicualris oculi muscle closes the eye tightly. The palpebral part is involved in normal blinking.
lacrimal gland two types of production
basal
reflex(irritation, emotional…)
some keys facts of the tear film produced by lacrimal gland
Has antibacterial properties due to the action of lysozyme
Basal and reflex secretion
Has a pH of around 7.6
An intact trigeminal nerve is required for reflex tear production (EG: diabetic neuropathy stops this leading to dry eyes)
film tear nerves (sensation and motor)
Sensation = 5th nerve – tells the brain that the eye needs tears Motor = 7th nerve parasympathetic fibres
what are the two types of conjunctiva?
The inner surface of the eyelids is covered by the palpebral conjunctiva. The eyeball is lined by the bulbar conjunctiva.
what is the difference between the two types of conjunctiva
The palpebral conjunctiva is more vascular than the bulbar
Follicles and papillae can be seen on the palpebral conjunctiva
Contains goblet cells which secrete part of the tear film
what causes papillae to be seen on palpebral conjunctiva?
allergy (hay fever, wearing contact lenses too long)
what causes follicles to be seen on palpebral conjunctiva?
adenovirus conjunctivitis (due to swimming/URTI), feel LN to decide cause (LN present=adenovirus=not dangerous)
cornea structure (5 layers)
epithelium (turnover every 48Hrs, symptoms fine in corneal abrasion), bowman’s membrane, storma (largest part), descemet’s membrane, endothelium (lose as get older, not replied) -[sup to deep]
Keratoconus
thinning of cornea
what happens to the lens with age? lens structure?
loses elasticity and so become bifocal/verifocal glasses dependant (poor regeneration properties)
The outermost part of the lens is known as the cortex, inner part is the nucleus
what attaches the lens to the ciliary body? how does this allow function?
the zonules.
A decrease in tension of the zonular fibres allows for near focussing
if you want to see something closer, what happens to the lens?
becomes shorter/fatter
what 3 parts does the Uvea contain?
iris, ciliary body, choroid
uvea function
blood supply/nutrition
pigment (to capture light and prevent light scatter)
how is aqueous humour produced?
Aqueous humour is produced by filtration of blood at the ciliary processes but is also actively secreted
aqueous humour route
Aqueous humour flows from posterior chamber to the anterior chamber and drains into the canal of Schlemm and Trabecular meshwork
IOP causes and results in?
inc secretion and reduced clearance
glacoma, optic nerve damage
WBCs in aqueous (foggy/flare) means what?
uveitis (inflammation lead to discharge of WBC), give glucocorticoids (in eye/oral)
pain + photophobia + red eye
uveitis, give glucocorticoids (in eye/oral)
describe the pupillary reflex
light → optic nerve →crossover →pre-tectal nucleus →crossover and to Edinger-Westphal nucleus = why both pupils contract
[slide 25]
sympathetic pathway
hypothalmus, contorls autonomic pathways, symps in C-spine, superior cervical ganglion, travels along arterils
potential interruption to the sympathetic pathway (causes horner’s)
pancoast tumour at superior cervical ganglion
carotid dissection along arteries (painful horner’s)
what is the accommodation reflex? what is the stimulus?
helps focus (lessens as become older) The stimulus for the reflex is a blurred image on the retina
the third nerve (CNIII)
Oculomotor nerve
controls all IO muscles except LR and SO - plays role in accommodation reflex
In a complete third nerve palsy what occurs? how can complete third nerve palsy occur?
the eye is positioned down and out with ptosis
how can complete third nerve palsy occur?
poor controlled diabetes/hypertension can cause, improves over 6-8 weeks
non-resloving: 3rd nerve lies close to posterior communicating artery and is vulnerable to aneurysms there, do scan and surgery
what is the 4th CN? where does it arise from?
The trochlear nerve is unique in that it arises from the dorsal aspect of the brainstem and crosses over
where does CN IV enter the eye? what does it do?
via the superior orbital fissure.
supplies superior oblique muscle
CN V arises from where?
The trigeminal nerve arises from 3 nuclei in the midbrain and medulla. [ophthalmic division most important for ophthalmology]
the ophthalmic division (CN V1) conveys does what?
supplies the tip of the nose (nasociliary branch)
conveys the afferent arm of the corneal reflex
what is Hutchison’s sign?
redness of tip of nose due to singles (VZV), tip of nose is end of CN V1 therefore check eye involvement.
CN VI name, function?
abducens nerve,
supplies the motor innervation to lateral rectus
where does the 6th nerve pass through?
the middle of the cavernous sinus (not the wall)
what causes Abducens nerve palsies?
raised intracranial pressure stretches the nerve
The 6th nerve arises from its nucleus in the pons
where do the 4 rectus eye muscle arise from?
common tendinous ring
painful eye movements?
optic neuritis, think MS.
because the optic nerve sheath is attached to the common tendinous ring
which is the strongest and thickest of the recti?
medial
what does a blowout # typically entrap?
the inferior rectus
where is the high density area that most cones are found
fovea
what are the rods/cones embedded in?
cuboidal epithelium
what gives rise to the optic nerve?
The ganglion cells
why must light pass though the ganglion cells before hitting the cones/rods?
bc the retina is inverted (posterior = photoreceptors, then ganglions, the forming optic nerve, then arteries/veins.)
what is the optic nerve encase in?
the meninges
where is the blind spot (optic nerve) located?
15 degrees temporally in the visual field
which fibres decussate at the optic chasm and which don’t?
nasal fibres decussate, while temporal fibres continue ipsilaterally.
learn the optic pathway and what interruptions cause which problem.
slide 38
blood supply to the eye?
ophthalmic artery is a branch of the internal carotid (end artery = 90mins to save or blind)
when looking at fundoscopy how can you tell which eye it is?
optic disc on left = left eye.
what to look for on fundoscopy?
colour, contour, cup
what will optic neuritis/raised ICP do on fundoscopy?
Fluffy contour of optic disc
what colour should optic disc be on fundoscopy?
pink, white = bad (ischema?)
how to tell difference between artery and vein on fundoscopy?
artery = elastic/muscly vein = dark red
Retinal veins appear thicker than retinal arteries (on fundoscopy) as arteries have a muscular tunic
Central Retinal Arterial Occlusion occurs, what to do? what is seen on fundoscopy?
refer to stroke unit (high risk of stroke).
blindness unless <90mins
red dot (macula as has own blood supply) while rest is white with oedema
venous drainage of the eye
The superior ophthalmic vein leaves the eye via the Superior orbital fissure
The vein drains into the cavernous sinus
Retinal vein occlusions are very common
sensory supply of the eye
The long and short ciliary nerves become part of the nasociliary nerve of the trigeminal; The cornea has a rich supply of free nerve endings
however, the retina has receptors for light only
flashes of light, bloody floaters, (no pain)
retinal detachment - macula on and off = different prognosis/urgency of treatment
risk factors for retinal detachment
trauma, previous surgery/detachment, being short sighted (marina’s = spontaneous)
what is most vulnerable in trauma
The inferior wall of the orbit.
medial wall thinnest
what passes through the supraorbital notch
The supraorbital nerve and vessels (can be damaged on trauma) - pain/pressure point of GCS
what do patients with blowout # commonly complain of?
pain on upgaze
