General mcqs Flashcards
which bones make up the medial wall of the orbit
maxilla, lacrimal, ethmoidal, sphenoid
what nerves pass through the superior orbital fissure
lacrimal nerve
frontal nerve
trochelar nerve
superior branch of the oculor motor nerve
superior branch of the opthalmic vein
nasocillary nerve
inferior branch of oculomotor nerve
inferior branch of opthalmic vein
abducens nerve
which nerves that travel within the sof pass within the common tendinous ring
- snia
superior division of the oculomotor nerve
nasocillary nerve
inferior branch of the oculomotor nerve
which nerves that travel within the superior orbital fissure rtravel outside the ctr
lacrimal
frontal
trochlea
superior branch of opthalmic vein
list the contents of the annulus of zinn
- oc- optic canal, optic nerve and opthalmic artery
- so- superior divison of the oculomotor nerve
- n- nasocillary nerve
- io- inferior divison of oculomotor nerve
- a- abducens nerve
which of the paranasal sinuses are most vunreable to blow out fractures and why
ethmoid and maxillary sinuses - the inferior wall seperating the orbit from the maxillary sinus
and medial walls seperating the orbit from the ethmoidal sinus are very thin
what are the four anterior foramen
superiororbtial formanen - supraorbital nerve
infraorbital formane - infraorbital nerve
zygomaticofacial foramen- zygomaticofacial nerve
zygomaticotemporal foramen - zygomaticotemporal nerve
where would you expect to see a lesion in a patient presenting with a left homonymous heminaipoia
right optic tract
where would you expect to see a lesion in a patient presening with a bitemporal hemianopia
- optic chiasm
where woulod you expect to see a lesion in a patient presenting with a right homonymous inferior quadrantopia
left parietal optic radiation
where would you expect too see a lesion in a patient with a left homonymous hemianopia with macular sparing
right visual cortex
what are the four parts of the optic nerve and which of them has the longest course
- intraocular
- intraorbital
- intracananicular
- intracranial
the longest portion is the intraorbial part which is around 25mm- 30mm long
what are the main differences between the magnocellular and parvocellular pathways
magnocellular
larger cells
faster conduction
involves heavily myleinated parasol retinal ganglion cells
involved in
motion
depth perception
high contrast vision
corresponds to 10% of nerve fibres
parvocellular
- smaller cells
slower conduction
involves midget retinal ganglion cells which are less heavily myleinated
involved in -
colour vision
fine high resoloution vision
low contrast vision
corresponds to 90% of the nerve fibres
describe the 6 layers of the lgn in terms of their input (i.e. laterality and visual input)
contralateral- 1, 4 , 6
ipsilateral - 2 , 3 , 5
magnocellular - 1 and 2
parvoceullar - 4 and 6
what is the main constituent of aqeuous humour
water
what structures produces aqeuous humour
non pigmented epithelium of the pars plicata
what is gonioscopy and what is it used to measure
angle of the anterior chamber
what avascular structures are nourished by the aqueous humour
- lens , zonules , anterior virteous
what is the normal introcular presssure approxiamtley in mmhg
10-21mmhg
describes the conventional route of aqueous drainage
- aqueous produced in the non - pigmented epithelium of the pars plicata of the cillary body
drains anterioly around the iris edge and drains via the conventional route
(90%)
- drains through trabecular meshwork in the angle of the anterior chamber
- flows into the canal of schlemm and the episcleral veins
describe the unconventional route of aqueous drainage
aqueous is produced in the non - pigmented epithelium of the pars plicata of the cillary body
drains anterioly around the iris edge and then drains through
10% via the uncoventional route - drains through the anterior face of the cillary body and iris root and passes into the cillary muscle and suprachoroidal space
from there it is drained by uveal and scleral veins
why does the cornea have a higher refractive in the mamillian eye compared to the crystaline lens
the 2 main factors
higher difference in refractive index of the air/tear film interface compared to the aqueous/ lens interface
- smaller radius of curvature of corneal surface compared to the lens (cornea is more curved than the lens)
describe the main adaptations of the cornea to maintain transparency
- avascular
smooth epithelium
regular arrangement of the collagen in stroma
maintained in a state of relative dehydration by the corneal endothelium
name the 5 corneal layers
- corenal epithelium
- bowmans layer
- stroma
- descements membrane
- corneal endothelium
which corneal layer is responsible for regulating the state of hydration of the corneal stroma - what happens when this fails - what conditons affect the corneal layer
endothelium
failure leads to corneal odema and loss of transparenc
this may happen in conditions like fucks endotheliel dystrophy
the corneal endothelium has epithelilel cells - explain this dichotomy
- epitheliel cells refers to cells that lie on a basemement membrane
- since the corneal endotheliel cells have a basement membrane (descements) they are said to be of the epitheliel cell type
what are the components of the accomodation reflex
- miosis
- increase in lens thickness (due to cllary muscle contraction and slackening of the zonular fibres)
- convergecne of the eyes
list 5 causes of cataracts besides age
- trauma and surgery
- diabetes
- steroids
- radiation
- genetic predispositon
- congential- rubella
where is the virteous base most strongly attached to the retina
ora serrata - virteous base
describe the consituent layers of the anterior lamellae
- anterior lamellae
skin and obicularis
describe the layers of the posterior lamellae
- tarsus and conj
what is the main function of the obicularis oculi
orbital portion - volountary clouse of the lids
palpebral portion - volountary and involountary lid closure
a facial nerve palsy can lead to blindness - how can this happen
failure of obicularis/muscles can cause lagopathlamos (incomplete closure of the eyelid) exposure keratopathy and corneal ulceration
how is the levator palpabrae superioris different from mullers muscle
lps is a skeletal muscle and innervated by cn iii
mullers muscle is a smooth muscle innervated by the sympathetic nervous system
what is a chalazion
- blocked meibomian gland
- mainstay of treatment is conservative - warm compress and lid hygeine
how can entropian and an ectropian lead to blindness
entropian - eyelashes rubbing against cornea and corneal scarring (e.g. in a trachoma)
ectropian - exposure keratopathy
what are the three main parts of conjuctiva
tarsal, forniceal and bulbar
what are the three main germinal cell layers which layers are involved in the development of the eye
- ectoderm, mesoderm , endoderm
only ectodermal and mesodermal layers contribute to ocular devlopment
which of the secondary brain vesciles are the eyes derived from
- diencephalon
describe the formation of the lens placode and the lens vesicle
- as the optic vesicle develops as an outpoutching of the diencephalon - and overlying surface ectoderm is induced to devlop into the lens placode - the lens placode and the optic vesicle then start to simultaneously invaginate - until the lens placode seperates from the surface of the lens vesicle while the optic vesicle becomes the optic cup
how does the retina form the optic cup which germinal cell layer is it derived from
- the thick inner layer of the optic cup develops into the neurosensory retina whilst the thinner outer layer devlops into the retinal pigmented epithelium - in between these two layers is the subretinal space
the retina develops from the neuroectoderm
what is the hyaloid artery and where does it travel
in the fetal eye the hyaloid artery provides blood supply to the retina as well as supporting the development of the lens - it travels through choridal fissure and enters the eye as the optic disc where it travels forward through the virteous (hyaloid canal) towards the lens
what is colomboma
a coloboma is (usually a inferonasal) defect in ocular structures such as the iris , cillary body , retina , choroid and optic disc
it results from a failure of closure of the choroidal fissure
what are the three main types of amblyopia and the causes for each
strabismic - squint with a dominant eye and a supressed eye
deprivational - congential catarcats capillary haemngioas obstructing visual axis
refractive - large difference in refractive errors between the two eyes
what are the three layers of tear film
- lipid layer
- aqueous layer
- mucinous layer
what is the function of the lipid layer
- limits evaporation of the aqueous component
what is the oily layer produced by
the meibomian glands, the glands of moll and ziess
what is the aqueous layer produced by
lacrimal and acessory glands
what is the function of the aqeuous layer
- nourishes , hydrates and immune defense
what is the function of the muscinous layer
- lubricates aids an even distribution of tears
what is the muscinous layer produced by
conjuctival goblet cells
the nasolacrimal duct drains into what structure
inferior meatus
what is dacrocytsis
- infection of the lacrimal sac
sesnroy innervation to the lacrimal gland is via which nerve
- lacrimal nerve
with reference to the parasympathetic supply of the lacrimal land , the preganglionic fibres travel along which nerve
greater petrosal nerve
what nerve is part of the symapathetic supply
the deep petrosal nerve
what are the consituents of circle of wilis
internal carotid artery
anterior cerebral artery
anterior communicating artery
posterior cerebral arteyr
posterior communicating artery
where do the dural venous sinuses lie in the brain - where do they receive blood from and where do they drain
- they recieve layers from the endosteal and meningeal layers of the brain
- drain blood from the cerebral veins as well as the csf into the internal jugular veins
how can infection around the danger zone lead ro opthalmoparesis (paralysis of the eom)
- infection can travel along the valveless venous system and spread to the carvenous sinus - this can affect cranial nerve 3 and 4 and 6 which all lie within the stryucture and thus lead to complete opthalmoparesis
how can internal carotid artery dissection lead to a horners sybdrome
postganglionic sympathetic fibres travel along the ica an ica dessection can therefore lead to a third order postganglionic horners
what forms the blood retinal barrier
zona occludens/ tight junctions between endotheliel cells of cra capillaries
zona occludens/ tight junctions between cells of retinal pigmented epithelium
tight junctions - multiprotein complexes which form a scaffolding between the endotheliel cells of the central retinal artery capillaries and between cells of the retinal pigmented epithelium to form the zona occludentes
which branches of the opthalmic artery is the choroidal circulation dervied from
cillary arteries - long , short and anterior
in which retinal layer do the phototeceptor cell bodies lie
- outer nuclear layer
what is meant by on and off bipolar cells
on bioplar cells - depolarised by light
off bipolar crells - hyperpolarised by light
which axons from the optic nerve
describe the myleination of these axons in terms of where it starts and the glial cell responsible for it
ganglion cell axons form the optic nerve
they are unmyleinated within the retina
and become myleinated by oligdodendrocytes as they travel past the lamina cribrosa in the sclera
describe how layer 2 of the lgn would recieve its input from a photoreceptor
- layer 2 - ipislateral eye , magnocellular pathway, parasol retinal ganglion cell
layer 2 of the lgn recieves magnocellular input from the ipsilaeral eye - therefore parasol retinal gagnlion cells in the ipsilateral eye are involved and send their signals down their axons which travel via the optic nerve past the optic chiasm and synapse at the ipsilateral lgn in layer 2
describe the posterior pole
- lies temporal to the optic disc and is cone dominated
posterior pole is where the fovea and macular lie - high acuity vision , central vision and therefore much higher cone density
what structure forms the anterior boundary of the neuroal retina
ora serrata - the neural retina is thinest hear but firmly adherent
inner membrane is virteous and outer boundary is bruchs membrane
what is the anatomical structure which forms the boundary between myleinated and unmyleimated retinal ganglion cell axons
- the lamina cribosa , a fenestrated (mesh- like) network of fibres in the sclera at the optic disc
what are the photopigmenrs responsible for phototransuction in the outer segments of the photoreceptor cells called
- opsins
how many different types of cone photoreceptors are there
3 types of opsins with spectral sensitivities of varying wavelenghts corresponding to different parts of the colour spectrum
short wavelength (blue)
medium wavelength (green)
long wavelength (red)
what might be the clinical consequce of having fewer types of photoreceptors
inidivduals with muted or absent types of any of the three types of cones above devlop colour blindness and have diffciulty distingushing between particular coloiurs
what happens after a photon is absorbed by a opsin in phototransduction
results in hyperpolarisation of the cell and cessation of glutamate release
what bones make up the inferior wall
paletine , maxilla , inferior
what are the contents of the sof
lacrimal, frontal , trochlear , superior division of the oculomotor nerve , nasocillary nerve , inferior division of the oculomotor nerve , abducens nerve
which nerves passes through the sof within the ctr
superior division of the oculomotor nerve
nasocillary nerve
inferior division of the oculomotor nerve
abducens nerve
what nerves of the sof pass outside the ctr
lacimal, frontal , trochlear
what nerves pass through the sof within the ctr most superiorly
superior division of the oculomotor nerve
which of the paranasal sinuses is the most common transmission of infection in orbital cellulitis
ethmoid
which veins are drained into the conventional route
- episcleral veins
what is the trabecular meshwork formed from
the trabecular meshwork is formed of three fenestrated layers
what is aqueous humour produced by
the non - pigmented epithelium of the pars plicata of the cillary body
what embryological layer does not contribute towards the development of the eye
- endoderm
what structure in the eye develops from mesoderm
- choroid
what struture develops from surface ectoderm
- the lens
