Eye anatomy

what is the function of lateral rectus muscle?

moves eye outward (abduct)

what innervates lateral rectus?

abducens nerve (CN VI)

what is the function of medial rectus?

• moves eye inward (adducts)

• used for convergence/near

what innervates medial rectus?

oculomotor nerve (CN III)

what is the function of superior rectus?

• elevates the eye

• upward gaze

• tracking objects moving vertically

what innervates superior rectus?

• oculomotor nerve (CN III)

what is the function of inferior rectus?

• depresses the eye

• downward gaze

what innervates inferior rectus?

oculomotor nerve (CN III)

what is the function of superior oblique?

• depresses the eye

• abducts the eye (outwards)

• intorts the eye

what innervates superior oblique?

• trochlear nerve (CN IV)

what is the function of inferior oblique?

• elevates the eye

• abducts the eye

• extorts the eye

what innervates inferior oblique?

oculomotor nerve (CN III)

what are the 5 layers of the cornea?

1. epithelium

2. bowman’s layer

3. stroma

4. descemet’s membrane

5. endothelium

what is the oily layer of the tear film?

• outermost layer

• slows evaporation

• prevents outflow

• lubricates the eye

• smooth anterior refracting surface

what is the mucin layer of tear film?

• innermost layer of tear film

• hydrophilic - wetting agent

• uniform spread of tears

• stabilises the tear film

what produces the mucin layer of tear film?

conjunctival goblet cells and corneal epithelium

what produces the oily layer of tear film?

meibomian and zeis glands

what is the aqueous layer of tear film?

• middle layer of tear film

• water-soluble nutrients & oxygen

• hydrates

• antibacterial and anti-viral

what secretes the aqueous layer of tear film?

the lacrimal glands

where is aqueous humour produced?

ciliary body

what is the function of the olfactory nerve?

• sensory nerve

• sense of smell

• olfactory receptors in the nasal cavity send signals to the olfactory bulb and brain

where does olfactory nerve (CN I) exit?

cribriform plate of the ethmoid bone

what is the function of the optic nerve?

• sensory nerve

• responsible for vision

• carries visual information from retina to the brain

• signals are processed by the occipital lobe

what is the exit location of the optic nerve (CN II)?

optic canal (sphenoid bone)

what is the function of oculomotor nerve?

• motor nerve

• controls most eye movement (IR, SR, MR, IO)

• controls pupil constriction (via parasympathetic fibres)

• controls eyelid elevation (levator palpebrae superioris)

• lens accommodation via parasympathetic fibres

where does oculomotor nerve (CN III) exit?

superior orbital fissure

what is the function of the trochlear nerve?

• motor nerve

• innervates the superior oblique which allows the eye to move downward and laterally

where does the trochlear nerve (CN IV) exit?

superior orbital fissure

what is the function of the trigeminal nerve?

combination nerve: both sensory and motor

• sensory: provides sensation to the face (touch, pain, temperature) and corneal reflex

• motor: controls muscles of mastication (chewing)

• has 3 branches that serves different areas of the face and head

where does trigeminal nerve (CN V) exit?

there are 3 branches of trigeminal nerve:

• V1 (ophthalmic): superior orbital fissure

• V2 (maxillary): foramen rotundum

• V3 (mandibular): foramen ovale
  

what is the function of the abducens nerve?

• motor nerve

• innervates the lateral rectus which abducts the eye

where does the abducens nerve (CN VI) exit?

superior orbital fissure

what is the function of the facial nerve?

combination of sensory and motor function

• sensory: taste sensation from the anterior two-thirds of the tongue

• motor: controls the muscle of facial expression (smile, frown)

• parasympathetic: stimulates lacrimal (tear) and salivary glands (submandibular/sublingual)

where does the facial nerve (CN VII) exit?

internal acoustic meatus (enters temporal bone)

what are the divisions of the facial nerve?

• temporal branch: to forehead and eyes

• zygomatic branch: to cheek muscles

• buccal branch: muscles of the cheek

• mandibular branch: lower lip and chin

• cervical branch: platysma and neck

what is the function of the vestibulocochlear nerve?

• sensory nerve

• responsible for hearing (cochlear part)

• responsible for balance (vestibular part)

• sends auditory information from the cochlear and equilibrium data from the vestibule to the brain

where does the vestibulocochlear nerve exit (CN VIII)

• internal acoustic meatus

what is the function of the glossopharyngeal nerve?

• combination of sensory and motor

• sensory: taste from the posterior one-third part , sensation from the pharynx

• motor: controls the muscle involved in swallowing

• parasympathetic: salivation (parotid gland)

where does the glossopharyngeal nerve (CN IX) exit?

jugular foramen

what is the function of the vagus nerve?

• combination of sensory and motor

• sensory: taste from the epiglottis and pharynx

• motor: muscles of the larynx and pharynx involved in swallowing and phonation

• parasympathetic: controls the heart, lungs and digestive tract

where does the vagus nerve (CN X) exit?

jugular foramen

what is the function of the accessory nerve?

• motor nerve

• controls the sternocleidomastoid and trapezius muscles to turn the head and shrug the shoulders

where does the accessory nerve (CN XI) exit?

jugular foramen (spinal root enters via the foramen magnum)

what is the function of the hypoglossal nerve?

• motor nerve

• controls the intrinsic and extrinsic muscles of the tongue involved in speech, swallowing and food manipulation

where does the hypoglossal nerve (CN XII) exit?

hypoglossal canal

what is the function and origin of the orbital part of the orbicularis oculi?

• originates from medial palpebral ligament

• deep insertions into the lacrimal sac

• innervated by the facial nerve (CN 7)

• holds the lower lid against the eye

• largest part of the orbicularis oculi

function: closes the eyes tightly

• voluntary: crying, excessive laughing, sneezing

• additional protection (increased thickness)

• prevents tears flowing into punctum
  

what is the function of the palpebral part of the orbicularis oculi?

• closes the eye without effort

• used for blinking

• can blink involuntarily e.g. blink reflex to a threat, spread tears over dry cornea, pump away excess tears

how does the lower eyelid move?

• it does not have a muscle like the levator palpebrae

• even when looking down, it does not move

what is the function and origin of levator palpebrae?

• function: lifts the upper lid

• origin: sphenoid bone (lesser wing)

• it runs forward to superior tarsal plate

• lies between the superior rectus and the roof of the orbit

• a sheath encloses the superior rectus and levator muscle to each other —> allows for coordinated eye movements with eyelid position (elevation of eyelid with upgaze)

what is the function of retinal ganglion cells?

what are bipolar cells in the retina?

what are amacrine cells in the retina?

what are horizontal cells in the retina?

what are rod cells in the retina?

what are cone cells in the retina?

what is the function of the lateral geniculate nucleus (LGN)?

what is this VF defect called?

right incongruous homonymous hemianopia

function of internal limiting membrane

• basement membrane formed by Muller glial cells

• separates retina from vitreous humour

function of nerve fibre layer

• contains axons of ganglion cells that converge to form the optic nerve (CN II)

function of ganglion cell layer

• contains cell bodies of ganglion cells

function of inner plexiform layer

• synapses between bipolar, ganglion, and amacrine cells

function of inner nuclear layer

• contains bipolar, amacrine, horizontal, and Muller cells

function of outer plexiform layer

• synapses between bipolar cells and photoreceptors

function of outer nuclear layer

• contains cell bodies of rods and cones (photoreceptors)

function of external limiting membrane

• tight junctions between photoreceptors and Muller cells

function of photoreceptor layer

• contains outer and inner segments of rods and cones

function of retinal pigment epithelium (RPE)

• nourishes photoreceptors

• absorbs stray light

• forms blood-retina barrier