The Orbit and the Eye Flashcards
describe the general structure of the bony orbit?
pyramidal structure
what forms the peak at the top of the pyramid?
optic canal (at the back in the middle)
what forms the roof of the bony orbit?
frontal bone
what forms the medial wall of the bony orbit?
ethmoid frontal lacrimal maxilla components of each
what forms the floor of the bony orbit?
mainly maxilla
what forms the lateral wall of the bony orbit?
zygomatic
sphenoid
which walls of the bony orbit are most likely to fracture and why
medial and inferior walls
very thin
what structures are in place to protect the eye when subjected to a direct blow?
eyes are deep set
frontal, zygomatic, nasal bones etc all sit further out than the eye
orbital rim is thick and strong to resist fracture
what is an orbital blow out and what can happen with this?
direct blow to the eye in between the bones of the orbit
increases the pressure in the eye
this increased pressure can cause walls to fracture and the contents of the eye to protrude through
can cause damage to nerves (e.g infraorbital NVB)
how can an orbital blowout cause sensory deficit in the face?
infraorbital NVB passes through the infraorbital foramen and then out through the maxilla to provide sensory innervation to the face
blowout fracture damaging the orbital floor can therefore cause sensory damage in the face
what are the 4 components of the eyelid?
outer skin
inner conjunctiva
eyelashes
glands
what is contained within the eyelids?
tarsal plate
orbicularis oculi
levator palpebrae superioris
what does the tarsal plate do?
maintains shape
contains meibomian glands which secrete lipids
which nerve innervates the orbicularis oculi muscle in the eyelid?
CN VII (facial nerve)
what does the levator palpebrae superioris do and which nerve innervates it?
opens the upper eyelid
innervated by CN III
what can cause ptosis and why?
CN III palsy as CN III innervated levator palpebrae superioris
what does the orbicularis oculi muscle do?
surrounds the eye
contraction closes the eye
describe the surface anatomy of the eye
white sclera (covered by conjunctiva)
iris (covered by cornea)
- sclera and cornea are continuous and iris sits deep to these
limbus = corneoscleral junction (junction between cornea and sclera)
lacrimal glands in the upper lateral quadrant
what is conjunctiva?
defensive barrier to small foreign objects (dust, insects etc)
describe the lacrimal apparatus/pathway and how crying is connected to the nasal cavity?
lacrimal gland produces tears (supplied by CN VII - parasympathetic supply)
blinking washes these tears across to the medial angle of the eye
tears drain through tiny lacrimal puncta in the medial angle
tears drain into the canaliculi and then into the lacrimal sac
tears then pass into the nasolacrimal duct which connects the nasal cavity with the eye
tears reach inferior meatus of the nasal cavity
what are the 3 layers of the eyeball?
fibrous outer layer
uvea (vascular) middle layer
retina (photosensitive) inner layer
what are the 2 parts of the fibrous outer layer of the eyeball?
sclera = white, fibrous cornea = for refraction of light
what are the 3 parts of the uvea?
iris
ciliary body
choroid = nutrition and gas exchange
what does the ciliary body in the uvea do?
controls iris, shape of lens and secretion of aqueous humour
what are the parts of the retina?
macula
optic disc
cones and rods
neural tissue
what is the anterior segment of the eye and what are the 2 chambers contained within it?
anterior segment = in front of lens
anterior chamber = between cornea and iris, contains aqueous humour
posterior chamber = between iris and suspensory ligaments, contains aqueous humour
what is the posterior segment and what is contained within it?
behind lens
makes up 2/3rds of the eye
contains vitreous body
what is vitreous body?
mixture of vitreous humour
common site of floaters in the eye
aqueous humour vs vitreous humour?
aqueous humour is continuously produced
vitreous humour present at birth and not replaced, thick and gelatinous and holds retina up against the eyeball
what can too much aqueous humour cause?
increased pressure in the eye leading to glaucoma
describe the path of circulation of aqueous fluid
ciliary processes in ciliary body produce aqueous fluid
aqueous fluid circulates within the posterior chamber and nourishes the lens
aqueous then passes through the pupil into the anterior chamber and nourishes the cornea
aqueous fluid is then reabsorbed into the scleral venous sinus (canal of schlemm) at the iridocorneal angle
what is the iridocorneal angle?
the angle formed by the iris and the cornea to allow drainage of aqueous humour
the “angle” in “open angle” and “closed angle” glaucoma
what can blockage of the canal of schlemm cause?
can increase pressure and cause ischaemia of the retina and glaucoma
what is the arterial supply to the eye?
ophthalmic artery (branch of internal carotid) passes through the optic canal with the optic nerve
central artery of the retina then branches off the ophthalmic artery and travels in the middle of the optic nerve (end artery)
- central vein of retina also in middle of optic nerve
describe venous drainage of the orbit
superior ophthalmic vein above the eye
inferior ophthalmic vein blow the eye
anastomosis forms where superior and inferior ophthalmic veins can drain anteriorly into the facial vein or posteriorly the two veins can join to form the cavernous sinus via the superior orbital fissure
what is the danger triangle in the face and why is this the case?
upper lip and nose
area where infection is very dangerous as the venous drainage can drain the infection into the cavernous sinus
what are the 4 components of the retina?
fundus (fundoscopy) which contains:
- optic disc
- macula
- fovea
what is the optic disc?
point of CN II formation
only point of entry/exit for blood vessels and axons of CN II
blind spot
what is the macula?
greatest density of cones
good for colour vision
what is the fovea?
centre of the macula
1.5 mm depression
area of most acute vision
what are the 3 layers of the retina from outermost to innermost?
- axons of ganglion cells
- ganglion cells
- photoreceptor cells
why is the optic disc known as the blind spot?
there are no photoreceptors
what can complete interruption of flow in a retinal artery branch/retinal vein cause?
loss of an area of visual field corresponding to the area of ischaemia
what can complete interruption of flow in the central artery or vein cause?
monocular blindness
nerve fibres from where cross over in the optic chiasm?
nasal retina
what are the extra-ocular muscles of the eye?
4 straight muscles (rectus muscles) - superior rectus = to look up, up and in - inferior rectus = to look down, down and in medial rectus = eye adduction (medial) lateral rectus = eye abduction (lateral) oblique muscles (keep eye steady when head is moving) - superior oblique = rotates eye medially in the orbit, down and out - inferior oblique = rotates eye laterally in orbit, up and out
what nerves innervate the extra-orbital muscles?
LR6 SO4 AO3
- lateral rectus = CN6 (abducens)
- superior oblique = CN 4 (trochlear nerve)
- All others = CN 3
what does the superior oblique pass through before turning back on itself?
trochlear
