The orbit Flashcards
what bone forms the roof of the orbit
frontal bone
the frontal bone forms what parts of the orbit
roof, parts of medial and parts of lateral walls
the frontal bone has a notch for what
supraorbital nerve and artery
what deflects blows to the face away from the eyes
supraorbital ridge
what bone forms part of the lateral wall of the orbit (not frontal)
zygoma
what bone forms a large part of the floor of the orbit
maxilla
what bone forms the infraorbital foramen
maxilla
what passes through the infraorbital foramen
infraorbital branch of CNV2 exits skull via infraorbital foramen
what bone forms the naso-lacrimal duct
lacrimal
what is the purpose of the naso-lacrimal duct
carries excess lacrimal fluid (tears) into the nasal cavity
what bone forms part of the medial wall of the orbit but also contributes to the nasal cavities
ethmoid bone
what is the butterfly shaped bone in the skull called
sphenoid bone
what foramina does the sphenoid bone form
optic canal
superior orbital fissure
contributes to the inferior orbital fissure
what passes through the inferior orbital fissure
ophthalmic veins
what nerves pass through the superior orbital fissure
CN III
CN IV
CN V
CN VI
there is a tiny contribution from what in wall of inferior orbital fissure
palatine
what is contained in the orbit
eyeball fat and connective tissue extra-ocular muscles nerves blood vessels
the orbital contents are protected anteriorly by what
orbital septum composed of strong connective tissue
the corners of the eyelid are supported by what
medial and lateral palpebral ligaments
what is the function of the tarsal plates
dense connective tissue which support eyelid. also contain glands that release oily fluid and watery secretions to lubricate the surface of the eye
what is the function of the check ligaments
restrict the movements of the extra-ocular muscles - restrict medial and lateral recti
what is the function of the suspensory ligament of the eye
supports the position of the eyeball within the orbit
what forms the outer coat of the eyeball
cornea and sclera - fibrous layers
what is the middle layer of the eyeball
vascular layer - iris, ciliary body and choroid
what is the inner layer of the eye
retina
what is the blind spot
area where the optic nerve leaves the eye so it is void of rods and cones
what is the area of the retina that is rich in both rods and cones
macula lutea (fovea)
where is the anterior chamber of the eye
between the lens and the cornea
what is in the anterior chamber of the eye
aqueous humor - thin fluid
what makes aqueous humor
cells of the ciliary body
how is aqueous humour recycled
recycled back into veins at the junction of the cornea and sclera
(corneo-scleral junction - canal of Schlemm)
what fills the posterior chamber of the eye
vitreous humour (gel)
what is the function of the vitreous humor
supports the retina by gently pressing it against the choroid below
the choroid has what
blood vessels that supply the retina
what are the 2 types of muscles associated with the eyeball
extra-ocular (Extrinsic) muscles
intra-ocular (intrinsic) muscles
what is the function of the extra-ocular eye muscles
move the eyeball within the orbit
what is the function of the intra-ocular eye muscles
change the shape of structures inside the eyeball
what is the name of the small radial muscle fibres that pass from edge of the pupil out across iris
dilator pupillae
what happens when fibres of dilator pupillae contract
medial edges of the iris are pulled outward increasing the size of the pupils
contracting dilator pupillae causes the pupil to ____ in size
grow
what is the innervation of dilator pupillae
sympathetic nervous system
the sympathetic nervous system innervates dilator pupillae to do what
pupil to dilate to give as much light to the retina as possible to detect danger and in low light to let enough light in to maintain retinal cell function
the iris also has circular fibres around the pupil called
sphincter pupillae
what happens when sphincter pupillae contracts
narrow the pupil, restricting amount of light getting into eye to protect the delicate retinal cells from high light intensities
what is the innervation of sphincter pupillae
parasympathetic control
the parasympathetic innervation to sphincter pupillae comes from what
carried by oculomotor nerve CN III
the sympathetic innervation of dilator pupillae comes from where
carried on blood vessels
how can you test oculomotor function
shine a light briefly in someones eye and if pupil constricts then oculomotor is working
what muscles act to change the shape of the lens for accomodation
ciliary muscles
what nerve supplies the ciliary muscle
oculomotor nerve (parasympathetic)
in the absence of nerve stimulation, the ciliary muscle is relaxed which causes the lens to do what
ciliary muscle relaxed
zonular fibres under tension
–> lens is stretched thin to refract light for distant vision
when the ciliary muscle receives nerve stimulation, it contracts causing the lens to do what
ciliary muscle contracts
zonular fibres relax
lens becomes more spherical to refract light for near vision
far vision requires a ____ lens and _____ ciliary muscle
thin lens
relaxed ciliary muscle
near vision requires a _____ and ____ ciliary muscle
fat
contracted
how many extra-ocular muscles are there
7