Anatomy Flashcards
What forms the apex of the orbit?
Optic canal
What bones form the lateral wall of the orbit?
Sphenoid
Zygomatic
What bone forms the floor of the orbit?
Maxilla
What bones form the medial wall of the orbit?
Lacrimal
Ethmoid bone
Frontal bone
Maxilla
What bone forms the roof of the orbit?
Orbital plate of the frontal bone
What is an orbital blow out?
Direct blow to eye can fracture the maxilla or ethmoid bone resulting in infraorbital neurovascular bundle damage
What nerve passes through the infraorbital foramen?
Facial nerve - causes sensory loss to skin
What features of the eyelid protects the eye?
Outer skin
Inner conjunctiva
Eyelashes
Glands
What is contained within the eyelid?
Tarsal plate (maintains shape) and meibomian lands to secrete lipids
Orbicularis oculi
Levator palpebrae superioris
What innervates the orbicularis oculi?
Facial nerve
What innervates the levator palpebrae superioris?
Parasympathetics from oculomotor nerve
What is the limbus?
Corneoscleral junction
What covers the white sclera?
Conjunctiva
What covers the iris?
Cornea
What gland produces lacrimal fluid?
Lacrimal gland situated in the upper outer quadrant of the orbit below the eyebrow
What is the pathway of lacrimal fluid from the lacrimal gland?
Supplied by facial nerve
Fluid washes over eye
Pushed towards medial angle
Drains through lacrimal puncta through the canaliculi canal to the lacrimal sac
Will drain through the nasolacrimal duct to the inferior meatus of the nasal cavity
What forms the fibrous layer of the globe?
Sclera - white and fibrous
Cornea - transparent and allows for refraction of light
What forms the uvea of the globe?
Iris - pupil diameter
Ciliary body - controls iris, shape of lens and secretion of aqueous humour
Choroid - nutrition and as exchange
What forms the retina?
Macula
Optic disc
Where is the anterior segment of the eye situated?
In front of lens
Divided into anterior and posterior chambers
What is contained within the anterior chamber of the anterior segment of the eye?
Between cornea and iris
Contains aqueous humour
What is contained within the posterior chamber of the anterior segment of the eye?
Between iris and suspensory ligament and contains aqueous humour
Where is the posterior segment of the eye situated?
Behind lens
2/3rd of eye
What is contained within the posterior segment of the globe?
Vitreous body
Vitreous humour
Common location for floaters
Can vitreous humour be made?
No, it is not produced in the eye, if it is damaged it will not come back
Can aqueous humour be made?
Yes, it is made in the ciliary process of the eye
What is the flow of aqueous humour in the eye?
Made in the ciliary process of the ciliary body
Circulates within the posterior chamber and nourishes lens
Passes through pupil into the anterior chamber to nourish the cornea
Reabsorbed into the scleral venous sinus via the canal of schlemm at the iridocorneal angle
What is the iridocorneal angle of the eye?
Angle in open angle and closed angle glaucoma
Raised intraocular pressure can cause ischaemia of the retina and glaucoma
What artery supplies the orbit?
Ophthalmic artery which is a branch of the internal carotid artery
What is contained within the optic canal?
Optic nerve and ophthalmic artery
What artery and vein run through the optic nerve?
Retinal artery and vein
What veins drain the eye?
Superior and inferior ophthalmic vein which drain into cavernous sinus via the superior orbital fissure
Orbit also drains anteriorly into facial vein
What is the fundus?
Posterior area of retina where light is focused
What is contained within the fundus?
Optic disc
Macula
Fovea
What occurs at the optic disc?
Point of optic nerve formation
Only point of entry/exit for blood vessels and axons of optic nerve
Blind spot
What is contained within the macula?
Yellow area that has the greatest density of cones allowing for colour vision and the area of vision acuity
What is the fovea?
Centre of the macula which is the area of most acute vision
What are the 3 main layers of the retina going posterior to anterior?
Most posterior: photoreceptors
Middle: Ganglion cells
Anterior: Axons of the ganglion
Where do the retinal veins and arteries lie on the retina?
Anterior to the retina
Why is the optic disc the blind spot?
No photoreceptors
What will occur with complete interruption of flow in a retinal artery branch/ vein?
Loss of an area of visual field corresponding to the area of ischamia
What will occur with complete interruption of flow to the central artery/vein?
Monocular blindness
Where will light from the nasal retina provide vision?
Will cross over at the optic chiasma to provide peripheral vision
Where will light from the temporal retina provide vision?
Crosses at optic chiasma to provide central (nasal) vision
Where is light from the right visual field processed?
Left primary visual cortex
Where is light from objects in the lower visual field processed?
Upper part of the primary visual cortex
What are the 6 extra-occular muscles of the eye?
Superior oblique Inferior oblique Superior rectus Inferior rectus Medial rectus Lateral rectus
What is the action of lateral rectus?
Abducts eyeball
What is the action of the medial rectus?
Adducts eyeball
What is the action of the superior rectus?
Up and in
What is the action of the inferior rectus?
Down and in
What is the action of the superior oblique?
Down and out by itself; to test clinically you ask the patient to move the eye down and in
What is the action of the inferior oblique?
Up and out
What structure will the superior oblique muscle pass around?
Trochlear
What is the innervation of the lateral rectus?
Abducens nerve
What is the innervation of the superior oblique?
Trochlear nerve
What nerve supplies the medial rectus, inferior rectus, superior rectus and inferior oblique muscles?
Oculomotor
What is the sensory innervation of the ophthalmic division of the trigeminal nerve?
Forehead Upper eyelid Cornea Conjunctiva Skin of rot/bridge/tip of nose
What is the sensory innervation of the maxillary division of the trigeminal nerve?
Skin of the lower eyelid
Skin over maxilla
Skin of ala of nose
Skin/mucosa of the upper lid
What is the sensory innervation of the mandibular division of the trigeminal nerve?
Skin over mandible and TMJ
APART from the angle of mandible which is supplied by C2,3 spinal nerves
Describe the blink (corneal) reflex?
Sensory: action potential conduced from cornea via ophthalmic division of trigeminal nerve
Relayed down V where it will reach trigeminal ganglion, relayed through the trigeminal proper to arrive in pons
Motor: facial nerve to orbicularis oculi causing a blink
What levels of the spinal cord can sympathetic axons leave?
T1-L2
How do sympathetic axons reach the eye?
Presynaptic axons exit spinal cord at T! and will ascend within sympathetic trunk to synapse in the superior cervical sympathetic ganglion
Post-synaptic sympathetic axons enter internal and external carotid arteries where they will form a plexus on the surface of these arteries
The ophthalmic artery will carry the internal carotid plexus to the orbit
Where can parasympathetic axons leave the CNS?
Cranial nerves 3,7,9,10
Sacral spinal nerves
What cranial nerves carry fibres for the eyes and in what ganglia will they synapse?
3 and 7
Oculomotor synapses in ciliary ganglion
Facial will synapse in pterygopalatine ganglion
Where can the oculomotor nerve be found in the brain?
Connects with CNS at junction between midline and pons and passes through the cavernous sinus to exit via the superior orbital fissure
What action will the oculomotor nerve have?
Somatic motor to superior, medial and inferior rectus and inferior oblique as well as levator palpebrae superioris
What does the superior division of the oculomotor nerve supply?
Superior rectal
Levator palpebrae superioris
What does the inferior division of the oculomotor nerve supply?
Medial and inferior rectus
Inferior oblique
Ciliary ganglion
What is the action of ciliary nerves?
Control diameter of iris and refractive shape of lens
What is contained within the long ciliary nerve?
Sympathetics and relays somatic sensory fibres from conjunctiva and cornea. Important in blink reflex
What is contained within the short ciliary nerve?
Post synaptic sympathetic fibres
Post synaptic parasympathetic fibres
Somatic sensory fibres
What occurs within the ciliary ganglion?
Synapse of inferior division of oculomotor to the post synaptic parasympathetic fibres
What are the autonomic reflexes of the eye?
Maximal eyelid elevation in fight or flight Pupillary light reflex Focussing lens far and near vision Lacrimation reflex tear production Vestibulo-ocular reflex Oculocardiac reflex
What is the vestibulo-ocular reflex?
Turns the eyes in the opposite direction to a head movement to stabilise gaze on an object during head movement
CNS connections between vestibulocochlear, oculomotor, trochlear and abducens
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extraocular muscles or pressure on eye
CNS connections between ophthalmic division of trigeminal nerve and vagus nerve
What are the autonomic sympathetic functions in the eye?
Open eyes wider - to allow more light
Pupil dilation
Lens change to focus on far objects
Emotional lacrimation
What are the autonomic parasympathetic functions in the eye?
Allow orbicularis oculi to work
Pupil constriction
Lens change shape to allow focus on near objects
Reflex lacrimation
How do post-synaptic sympathetic fibres reach the levator palpebrae superioris?
Superior cervical sympathetic ganglion
Internal carotid nerve
Internal carotid plexus on surface of internal carotid artery
Plexus of axons carried on ophthalmic artery and on its branches to the orbital structures
What can cause pupil dilation?
Sympathetic axons in dim light, fight or flight and the sick patient
Mydriatic drugs
What muscle contracts to dilate the pupil?
Dilator pupillae fibres which are radially arranged around the iris - originate on external circumference of iris and inset on internal circumference of iris
What an cause constriction of the pupil?
Parasympathetics in bright light and “rest and digest”
Miotic pupil in horner’s syndrome
Opiate drugs - fixed, pin point
Blown pupil ( fixed dilated) in oculomotor pathology
What muscle will contract to cause dilation of the pupil?
Sphincter pupillae which is situated around the internal circumference of the iris
Will both eyes constrict when a torch is shone into one eye?
Yes - this is the pupillary light reflex
Describe the pupillary light reflex?
Special sensory is the ipsilateral optic nerve
CNS connections in midbrain
Motor limb of the reflex is the oculomotor nerves
Direct light reflex in stimulated eye
Consensual light reflex in non-stimulated eye
What 4 neurones are involved in the pupillary light reflex?
1st: Retinal ganglion cells pass to the ipsilateral optic nerve to the optic chiasm to synapse in the pretectal nucleus in the midbrain
2nd: located in the midbrain to connect the pretectal nucleus to the edinger westphal nucleus
3rd: pass from EW nucleus via inferior division of oculomotor nerve to synapse in ciliary ganglion
4th: short ciliary nerve to the sphincter pupillae muscles
What is contained within the edinger westphal nucleus?
Location of cell bodies of the parasympathetic axons of oculomotor nerve
What is the function fo the suspensory ligament?
Connects the circumference of the lens and the ciliary body
What is the ciliary body?
Muscular and vascular
Smooth muscle like a sphincter around the circumference
What will the ciliary body do in far vision?
Parasympathetic shut off
Ciliary body will relax and the suspensory ligaments tighten to flatten the lens
What will the ciliary body do in near vision?
Parasympathetic turned on
Suspensory ligaments relax and lens will become spherical to focus on near objects
What will the accommodation reflex clinically assess?
Bilateral pupillary constriction (CN 3): to prevent diverging light rays from hitting the periphery of the retina and resulting in a blurred image
Bilateral convergence - medial rotation of both eyes (CN 3)
Bilateral relaxation of lens (CN 3)
What are basal tears?
Important in corneal health
Clean/ nourish and hydrate the avascular cornea
Contain lysosomes to hydrolyse bacterial cell walls
What are reflex tears?
Extra tears in response to mechanical or chemical stimulation
Afferent limb is ophthalmic division of trigeminal nerve from cornea/conjunctiva
Efferent limb is parasympathetic axons originating from facial nerve
What are the symptoms of horner’s syndrome?
Ipsilateral: Miosis Ptosis Reduced sweating (anhidrosis) Increased warmth and redness Impaired sympathetic innervation to head and neck
What can cause horner’s syndrome?
Root of neck trauma Carotid dissection Internal jugular vein engorgement Deep cervical node mets Pancoast tumour (lung apex)
