the orbits and contents (eye) (A20) Flashcards
protection of our eyeballs
- bony orbits
- eyelids
- tears
- sensory nerve supply and the blink reflex (very relevant to dentists as eyes are within the operative field of the dentist)
components that help us to ‘see’
- anatomy of the eye (optic nerves)
- extraocular muscles (how we move our eyes)
extraocular muscles
muscles involved in movement of eyes
bones of the orbit
- roof of orbit (orbital plate of the frontal bone containing anterior and posterior ethmoidal foramen)
- apex (at optic canal through sphenoid bone medial to lesser wing of sphenoid bone and superior to tiny section of palatine bone)
- lateral wall of the orbit (greater wing of sphenoid, lateral to superior orbital fissure and lesser wing of sphenoid and superior to inferior orbital fissure)
- floor of the orbit (maxilla bone- containing infraorbital canal which joins to infraorbital foramen)
- medial wall of orbit (ethmoid bone, lateral to lacrimal bone and lacrimal fossa)
- base (called the orbital rim) -> made up of frontal bone with supraorbital notch/foramen, maxillary bone with infraorbital foramen and canal, and zygomatic bone with zygomaticofacial foramen)
2 divisions of orbicularis oculi
- orbicularis oculi = muscle of facial expression
- 1.orbital part (surrounds the eyelids, used to screw up eyes)
2. palpebral part (within the eyelids, used in blinking)
components of eyelids (underneath palpebral part of orbicularis oculi)
- tendon of levator palpebrae superioris (contains skeletal and smooth muscle and attaches superior part of superior tarsal plate)
- superior tarsal plate/inferior tarsal plate (elongated plates of dense connective tissue found in each eyelid,upper and lower, and contribute to its form and support/make up palpebral part of orbicularis oculi)
- medial palpebral ligament (attaches to frontal process of maxilla and lacrimal bone) and lateral palpebral ligaments (the band that attaches the tarsal plates to the orbital eminence of the zygomatic bone)
- palpebral fissure (space between the open eyelids)
- orbital septum (fascia covering posterior aspect of orbicularis oculi)
conjunctiva
the mucous membrane that covers the front of the eye and lines the inside of the eyelids
tarsal gland
special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye’s tear film
-tendon of levator palpebrae superioris
contains skeletal and smooth muscle and attaches to superior part of superior tarsal plate
-superior tarsal plate/inferior tarsal plate
elongated plates of dense connective tissue found in each eyelid,upper and lower, and contribute to its form and support/make up palpebral part of orbicularis oculi
medial palpebral ligament
attaches to frontal process of maxilla and lacrimal bone
palpebral fissure
space between the open eyelids
orbital septum
fascia covering posterior aspect of orbicularis oculi
lateral palpebral ligaments
the band that attaches the tarsal plates to the orbital eminence of the zygomatic bone
sagittal section of eyelid (from deep to superficial)
palpebral conjunctiva -> tarsal glands -> superior tarsal plate (with levator palpebrae superioris attaching superiorly) -> palpebral orbicularis oculi ->skin
cornea
the transparent layer forming the front of the eye/translucent layer covering the iris
vessel visible from medial aspect of eye when looking up and pulling down on lower eye lid
conjunctival vessel (conjunctivitis)
are of conjunctiva at medial canthus
lacrimal lake (the small cisternlike area of the conjunctiva at the medial angle of the eye, in which the tears collect after bathing the anterior surface of the eyeball and the conjunctival sac)
medial canthus
inner corner of the eye, where the upper and lower lids meet
lateral canthus
the outer corner of the eye, where the upper and lower lids meet
opening to lacrimal duct/canaliculi
inferior and superior lacrimal punctum/puncta (one per eye lid) (swelling around this = inferior lacrimal papilla)
conjunctival fornix
the space formed by the junction of the bulbar and palpebral portions of the conjunctiva, that of the upper lid = the superior conjunctival fornix and that of the lower lid = the inferior conjunctival fornix
different types of conjunctiva
- palpebral conjunctiva (lining eyelids)
- scleral (bulbar) conjunctiva lining the sclera
sclera
the tough, white outer coat of the eyeball
location of lacrimal gland
in the upper lateral part of the orbit
function of lacrimal gland
produces tears (supplied by autonomic nervous system)
superior and inferior lacrimal canaliculi
- small canals
- also known as lacrimal ducts, these tube-like structures carry the tears from the eyes to the lacrimal sac
- openings to these = superior and inferior lacrimal punctum
lacrimal sac
- lies within the lacrimal fossa of the lacrimal bone
- drains tears from canaliculi to nasolacrimal duct
nasolacrimal duct
- aka tear duct
- a duct that carries tears from the lacrimal sac to the nasal cavity
components of the eyeball (globe)
- pupil (black component that you see through)
- iris (coloured component)
- sclera (white component covered by scleral conjunctiva)
layers of the eyeball
- fibrous layer
- vascular layer
- neural layer
- sclera->choroid->retina
fibrous layer of the eyeball
- The fibrous layer of the eye is the outermost layer. It consists of the sclera (white part) and cornea(transparent layer forming the front of the eye covering the iris), which are directly continuous with each other. Their main functions are to provide shape to the eye and support the deeper structures.
- The sclera comprises the majority of the fibrous layer (approximately 85%). It provides attachment to the extraocular muscles – these muscles are responsible for the movement of the eye. It is visible as the white part of the eye.
- The cornea is transparent, and positioned centrally at the front of the eye. Light entering the eye is refracted by the cornea.
vascular layer of the eyeball
- the vascular layer of the eye lies underneath the fibrous layer. It consists of the choroid, ciliary body and iris:
- > choroid = a layer of connective tissue and blood vessels on the outside of the retina, provides nourishment to the outer layers of the retina.
- > ciliary body = comprised of two parts – the ciliary muscle and ciliary processes (the ciliary muscle consists of a collection of smooth muscles fibres, these are attached to the lens of the eye by the ciliary processes, the ciliary body controls the shape of the lens, and also contributes to the formation of aqueous humor, ciliary body connects choroid to iris to complete the vascular layer )
- > iris = a circular structure/coloured component, with an aperture/hole in the centre (called the pupil that lets light in) - the diameter of the pupil is altered by smooth muscle fibres within the iris, which are innervated by the autonomic nervous system. (the iris is situated between the lens and the cornea)
lens
- posterior to iris
- important for focussing focussing
- shape of lens is determined by ciliary body (muscles and processes)
- The lens of the eye is located anteriorly, between the vitreous humor and the pupil. The shape of the lens is altered by the ciliary body, changing its refractive power
retina
-layer at the back of the eyeball containing cells that are sensitive to light and that trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed
sensory neural layer
- The inner layer of the eye consists of the retina, the light detecting part of the eye
- made up of retina (layer at the back of the eyeball containing cells that are sensitive to light and that trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed)
- supplied by central artery and vein
fovea centralis
= small depression in the retina of the eye where visual acuity is highest. The center of the field of vision is focused in this region, where retinal cones are particularly concentrated
-within macula (an oval yellowish area surrounding the fovea near the center of the retina in the eye, which is the region of keenest vision)
area where vision is highest
fovea centralis (in macula)
optic disc
-the raised disk on the retina at the point of entry of the optic nerve, lacking visual receptors and so creating a blind spot
chambers of the eyeball
- there are two fluid filled areas in the eye (known as the anterior and posterior chambers)
- > the anterior chamber is located between the cornea and the iris
- > the posterior chamber between the iris and ciliary processes, posterior chamber contains aqueous humor secreted by the ciliary body
- the chambers are filled with aqueous humor – a clear plasma-like fluid that nourishes and protects the eye
vitreous humor
- transparent jelly that supports the lens and retina
- jellylike tissue filling the eyeball behind the lens
area of most acute vision (most rods and cones)
macula
blind spot of the eye
-optic disc (the raised disk on the retina at the point of entry of the optic nerve, lacking visual receptors and so creating a blind spot)
blood supply to the retina
central artery and vein
ophthalmoscopy
-ophthalmoscopy = Examination of the interior of the eye, including the lens, retina and optic nerve, by indirect or direct ophthalmoscopy
-Posteriorly and laterally, both layers of the retina are present. This is the optic part of the retina.
The optic part of the retina can be viewed during ophthalmoscopy.
-The centre of the retina is marked by an area known as the macula. It is yellowish in colour, and highly pigmented. The macula contains a depression called the fovea, which has a high concentration of light detecting cells. It is the area responsible for high acuity vision/most acute vision. The area that the optic nerve enters the retina is known as the optic disc – it contains no light detecting cells therefore is a blind spot
ciliary body
- smooth muscles and blood vessels
- connects choroid to iris to complete the vascular layer
what connects the ciliary body to the lens
- suspensory ligament of the lens
- holds the lens in place
canal of schlemm
- aka scleral venous sinus
- drains the aqueous humor from the anterior chamber into the veins draining the eyeball
7 extraocular muscles
- all 7 = skeletal muscles therefore control the movement of our eyes
- 4 rectus (‘straight’) muscles
- > superior rectus
- > inferior rectus
- > medial rectus
- > lateral rectus
- 2 oblique muscles:
- > superior oblique
- > inferior oblique
- 7th = levator palpebrae superioris
4 straight extraocular muscles
- > superior rectus
- > inferior rectus
- > medial rectus
- > lateral rectus
2 oblique extraocular muscles
- > superior oblique
- >inferior oblique
common origin of all extraocular muscles
-all arise from common tendinous ring at location of optic canal and superior orbital fissure and insert onto sclera (white part) of eye ball
trochlea
- resembles a pulley (a wheel with a grooved rim around which a cord passes, acts to change direction of chord)
- the fibrous ring in the inner upper part of the orbit through which the tendon of the superior oblique muscle of the eye passes
which muscle passes through the trochlea
superior oblique muscle
levator palpebrae superioris
-arises from the same common tendinous ring, however attaches to superior tarsal plate, whereas the rectus and oblique extraocular muscles attach to the sclera
nerve supply to the extraocular muscles
- LR6 SO4 AO3
- > lateral rectus muscle is supplied by CNVI/abducent nerve
- > superior oblique muscle is supplied by CNIV/trochlear nerve
- > all other extraocular muscles are supplied by CNIII (oculomotor nerve)
- levator palpebrae superioris is also supplied by sympathetics (as well as CNIII)
clinical testing of CN III (occulomotor), CN IV (trochlear) and CN VI (abducent) (nerve supply to extraocular muscles)
- eyeball fully adducted to test medial rectus and superior and inferior oblique
- eyeball fully abducted to test lateral rectus then superior and inferior rectus
- does not matter whether you are testing the movements of the right or left eye
sensory nerve supply to the orbital region
- V1 supplies upper eyelid and cornea/conjunctiva:
- > lacrimal nerve
- > supraorbital nerve
- > supratrochlear nerve
- > infratrochlear nerve
- V2 supplies lower eyelid
- > infraorbital nerve
the blink reflex
- very relevant to dentists as the eyes are within the operative field of the dentist
- afferent (sensory) limb of the reflex = action potentials travel in V1 which is the nerve supply to the upper eyelid and cornea/conjunctiva and detects the stimuli of the cornea
- goes to the trigeminal ganglion where it synapses
- efferent (motor) limb of the reflex= action potentials travel in CN VII (facial nerve) to the palpebral part of the orbicularis oculi causing blinking
branches of ophthalmic division of trigeminal
- CNV2 travels lateral to cavernous sinus and exits cranial cavity via the superior orbital fissure
- Ophthalmic nerve gives rise to 3 terminal branches: frontal, lacrimal and nasociliary, which innervate the skin and mucous membrane of derivatives of the frontonasal prominence derivatives:
- forehead and scalp
- frontal and ethmoidal sinus
- upper eyelid and its conjunctiva
- cornea (see clinical relevance)
- dorsum of the nose
- > Parasympathetic Supply:
- lacrimal gland: Post ganglionic fibres from the pterygopalatine ganglion (derived from the facial nerve), travel with the zygomatic branch of V2 and then join the lacrimal branch of V1. The fibres supply parasympathetic innervation to the lacrimal gland
trigeminal ganglion
-located lateral to cavernous sinus
branches of CNV1 (ophthalmic division of trigeminal)
- leaves cranial cavity at superior orbital fissure
- frontal nerve (which further branches into supraorbital and supratrochlear)
- lacrimal nerve (which receives branch of zygomatic nerve of the maxillary division of trigeminal)
- nasociliary nerve (branches into anterior and posterior ethmoid nerves, and infratrochlear nerves)
- > anterior ethmoidal nerves become external nasal nerves
ophthalmic artery
- arises from internal carotid artery
- branches to central artery of retina, lacrimal artery, supraorbital artery, anterior and posterior ethmoidal arteries and supratrochlear artery
branches of internal carotid arteries
- once in the cranial cavity, the internal carotids pass anteriorly through the cavernous sinus. Distal to the cavernous sinus, each ICA gives rise to:
- > ophthalmic artery – Supplies the structures of the orbit
- > posterior communicating artery – Acts as an anastamotic ‘connecting vessel’ in the Circle of Willis (see ‘Circle of Willis’ below).
- anterior cerebral artery – Supplies part of the cerebrum.
- The internal carotids then continue as the middle cerebral artery, which supplies the lateral portions of the cerebrum
central artery of retina
- travels within optic nerve
- end artery (an artery with insufficient anastomoses to maintain viability of the tissue if arterial occlusion/ obstruction occurs, therefore can lead to blindness)
venous drainage of the eye (ophthalmic veins)
-venous drainage is via the superior and inferior ophthalmic veins, which drain into cavernous sinus
what travels through the anterior and posterior ethmoidal foramina
anterior and posterior ethmoidal vessels/arteries
danger triangle of the face
- superficial veins can carry infection into the cranial cavity
- the supraorbital vein drains into the superior ophthalmic vein
- the facial vein drains into the inferior and superior ophthalmic vein
- > the superior and inferior ophthalmic veins drain into the cavernous sinus therefore this is the entry of infection into the cranial cavity
what passes through the supraorbital foramen/notch
the supraorbital nerve (which is a branch of the ophthalmic division of trigeminal nerve)
