week 7 practical

name the 7 surface landmarks of the eyelid identifiable on a living subject

palpebral fissure and sulci, caruncle, plica semilunaris, grey line, meibomian orifices, punctum lacrimale, and papilla lacrimalis

what are the periorbital muscles

frontalis, corrugator supercilia, procerus and orbicularis oculi

what are the actions of the periorbital muscles (frontalis, corrugator supercilii, procerus, and orbicularis oculi)

frontalis elevates eyebrows (expression of surprise), corrugator supercilii pulls eyebrows medially and down (frowning/puzzled), procerus wrinkles skin over bridge of nose and orbicularis oculi closes eyelids

how can the frontalis muscle assist a patient with severe ptosis due to levator palpebrae superioris weakness

naturally, voluntary contraction of frontal lifts the skin of the forehead and eyebrow upwards but the attachments between the eyebrow skin and tarsal plate are loose and flexible so this contraction only creates slight traction and usually insufficient to lift a severely ptotic lid high enough to unlock the visual axis. with the surgery, a surgical material bridges the tarsal plate to the frontal muscle. this bypasses the non-functional elevator muscle by allowing the patient to contract their frontal muscle to lift the tarsal plate to open the upper lid and clear the visual axis

what are the three parts of the orbicularis oculi muscle, and what is the specific role of each

orbital part for forced, tight eye closure, palpebral part for gentle, regular blinking and lacrimal part (horner's muscle) to holds the eyelid margin tightly against the globe and aids tear drainage

which cranial nerve innervates the orbicularis oculi and all other muscles of facial expression

cn vii facial nerve

trace the complete lacrimal drainage pathway from the tear gland to the nasal cavity

lacrimal gland (superolateral) → sweeps across ocular surface via blinks → lacrimal puncta (superior/inferior) → canaliculi → common canaliculus → lacrimal sac (in fossa formed by lacrimal bone and frontal process of maxilla) → nasolacrimal duct → inferior meatus of the nose

into which bone does the medial palpebral ligament insert and why is its surgical position critical

into frontal process of maxilla and sits directly anterior upper part of lacrimal sac. mpl acts as the primary anatomical landmark to locate the lacrimal sac, identifying and carefully retracting it prevents surgical injury or missing the lacrimal sac during creation of the lacrimal-nasal bypass channel

what are the origin, insertion, and innervation of the levator palpebrae superioris (lps), and what smooth muscle assists it

origin at lesser wing of sphenoid above optic canal, insertion at superior tarsal plate and upper lid skin, innervated by cn iii, assisting superior tarsal muscle (müller's muscle), innervated by sympathetics

trace the complete parasympathetic (secretomotor) pathway to the lacrimal gland starting from the brainstem

cn vii (superior salivatory nucleus) → greater petrosal nerve → pterygoid canal → pterygopalatine ganglion (relays here) → maxillary nerve (v2) → zygomatic nerve → communicating branch → lacrimal nerve (v1) → lacrimal gland

state the origins, insertion, innervation and action for the four recti muscles

origin at annulus of zinn, mr antero-medial sclera 5.5mm from limbus, lr antero-lateral sclera 6.9mm, sr antero-superior sclera 7.7mm, ir antero-inferior sclera 6.5mm, lr innervated by CN VI the rest 3, mr for adduction, lr for abduction, sr for elevation, intorsion, adduction, ir for depression, extorsion, adduction

what is the origin, insertion, innervation, and primary action of the superior oblique muscle

body of sphenoid super-medial to annulus of zinn, insertion at postero-superior lateral sclera posterior to equator, innervated by CN IV, intorsion (primary), depression (secondary), abduction (tertiary)

what are the origin, insertion, innervation, and primary action of the inferior oblique muscle

origin is orbital floor antero-medial maxilla, insertion poster-inferior lateral sclera posterior to equator, innervated by CN III, action is extorsion (primary), elevation (secondary), abduction (tertiary)\

what is the difference between the orbital axis and the visual axis

orbital axis is the anatomical midline axis of the bony orbit pointing forward and outward (~23° lateral) visual axis is the direct optical line of sight from the fovea through the center of the pupil straight ahead

why do the vertical recti muscles have secondary and tertiary actions (torsion and adduction) instead of pulling in a pure vertical plane

because the orbital axis diverges from the visual axis by about 23°, meaning the vertical recti pull obliquely along the orbital apex rather than straight along the line of sight

why do both obliques act primarily as torsiometers and abductors

they attach to the posterior half of the eyeball and approach it diagonally at 51 degrees. because they wrap over the glob at this angle, their primary mechanical effect is torsion (twisting motion) around the line of sight and because they pull the back half of the eyeball medially toward the nose, the eyeball pivots in its socket and forces the front of the eye to swing outward (abduction)

why does the superior oblique depress the eye and the inferior oblique elevate it, despite inserting behind the equator

the eyeball rotates around a central axis within the orbit, acting as a pivot where displacement of the posterior globe produces an equal and opposite movement of the anterior globe. both oblique inserts on the posterior globe and pulls their insertion sits anteriorly toward their origin. so inserts onto the superior-posterior quadrant where pulling the top posterior globe anteriorly and superiorly tilts the eye downward and io inserts onto the inferior-posterior quadrant where pulling the bottom posterior globe anteriorly and inferiorly tilts the eye upward

what is the function of the trochlea, and what would happen if it were absent

fibrocartilaginous, u-shaped loop structure located on the superomedial orbital wall that redirects the tendon of the so muscle, allowing it to approach the globe from an anterior-medial angle. if the trochlea were absent, the so muscle would lack this pull and instead pull straight back from the apex like a rectus muscle, losing its ability to intort and depress

what is the primary effect on resting eye position and movement deficit when losing medial rectus

eye tuns out/exotropia because lr pulls unopposed, loss of adduction

what is the primary effect on resting eye position and movement deficit when losing lateral rectus

eye turns in/exotropia, loss of adduction

what is the primary effect on resting eye position and movement deficit when losing sr

eye sits lower/hypotropia and slight turn outwards/mild exotropia, loss of elevation greatest when looking 23 degrees outward/abducted

what is the primary effect on resting eye position and movement deficit when losing io

eye slightly sits lower/mild hypotropia and slight turn intward/mild esotropia, loss of elevation greatest when looking 51 degrees inward/adducted

what is the primary effect on resting eye position and movement deficit when losing ir

eye sits higher/hypertropia and slight turn outward/exotropia, loss of depression greatest when looking 23 degrees outward/abducted

what is the primary effect on resting eye position and movement deficit when losing so

eye sits higher/hypertropia and extorsion with px tilting their head toward the opposite shoulder to compensate, loss of depression greatest when looking inward/adducted

name and define the four primary types of eye movement

saccades, smooth pursuit, vergence, vestibulo-ocular reflex

what is saccades eye movement and its key feature

rapid, conjugate eye movements of both eyes that shift fixation rapidly from one target to another. during a saccade, visual input is briefly suppressed by the brain (saccadic suppression) so you dont experience a disorienting motion blur

what is smooth pursuit eye movement

continuous, voluntary, slow conjugate movements of both eyes designed to keep a moving visual target matched continuously on the fovea

what is vergence eye movement

disconjugate movements where both eyes move in opposite direction simultaneously to align both fovea’s on a target moving closer (convergence - eye adduct) or further away from face (divergence - both eyes abduct) to maintain single binocular vision

what is vestibulo-ocular reflex (vor) eye movement

involuntary, subconscious reflex movement of the eyes triggered by the vestibular system in response to head rotation. when the head rotates in one direction, the vor generates eye movement of equal magnitude in the opposite direction to keep the visual image stable on fovea during head movement

what happens when you attempt to make a smooth pursuit eye movement without a moving target, and what does this reveal about eye movement systems

smooth pursuit will fail and the eyes execute a series of saccades instead which reveals that smooth pursuit is a stimulus driven tracking system requiring a moving visual target and cannot be executed purely voluntarily