Orbit and Visual Pathways

How many extraocular muscles are there?

6 paired muscles 4 rectus 2 oblique Insert on sclera

What does common tendinous ring encircle?

CN II, opthalamic A, CN III, CN VI and nasociliary nerve, and four rectus muscles (Frontal N, lacrimal N and CN IV are excluded from the ring)

What are the motor nerves for the extrinsic eye muscles?

CN III, IV, VI

What is the superior oblique muscle innervated by

CN IV Trochlear nerve

What supplies sesnory from eyeball and from nasal cavity, upper face?

CN V1

What part of eye can be reshaped in lasik?

Cornea

What is the part of eye that is the most important refractive medium?

Cornea - avascular and sensitive (blue) (part that is reshaped with LASIK)

What is the major light refractive structure of the eye

Cornea - is also highly sensitive to touch

What happens in accommodation?

Elastic capsule of lens is round at rest, but held under tension by zonular fibers anchored to ciliary processes flattens the lens to allow for distant focus. Parasympaethic stimulation causes ciliary muscles to contract and bulge inwards, relieving tension on zonular fibers, allowing elastic lens capsule to become more rounded for close vision

What is the action of inferior oblique muscle?

Elevates, abducts and extorts pupil Combined action is to roll "up and out" by pulling back of eye medially and anteriorly from below

Where does nasociliary travel in orbit?

Enters common tendinous ring, *follows course of opthalamic artery* anteriomedially across orbit, superior to optic nerve in medial space *artery will be squiggly in lab

What does each optic nerve carry?

Entire visual field for ipsilateral eye

What composes the medial wall of the orbit?

Ethmoid (green) lacrimal (orange) maxilla -rim (red) and posteriorly by sphenoid (yellow) *very thin, often translucent - ethmoidal air cells; paranasal air sinuses on inner wall of medial side

What are the contents of the orbit?

Eyeball (but doesn't fill orbit) Lacrimal gland Extraocular muscles Neurovasculature Orbital fascia and orbital fat

What is the "resting gaze"?

Eyes at rest - looking straight ahead - muscles oppose each other to maintain this

What is the motor limb of the corneal reflex?

Facial motor nucleus fibers travel along ipsilateral CN VII (facial nerve) to stimulate orbicularis oculi muscle (blink) Superior salivary nucleus sends parasympathetic fibers along ipsilateral CN VII to stimulate lacrimal gland (tears)

What is the orbital septum?

Fibrous membrane that suspends tarsal palates from bony orbital rim - anchors eyelids to bony orbit

What is aqueous humor?

Fluid that fills posterior and anterior chambers of the eye - bathes and nourishes lens - flows through pupil and also nourishes cornea Drains into opthalamic veins at Schlemm's canal (at iridiocorneal angle)

What will make eyes appear sunken?

Loss of fat/malnutrition

visual field for each eye is divided into .........

Nasal and temporal portions (Nasal portions from each eye overlap to allow depth perception)

What does anterior and posterior ethmoidal nerve pierce and supply?

Purple Pierce medial wall with arteries to supply mucosa of sphenoid sinus, ethmoidal air cells, roof of nasal cavity and tip of nose

What does adducting eyes test?

Puts slack in superior and inferior rectus muscles Aligns visual axis with axis of pull for oblique muscles Tests medial rectus

What does abducting eyes test?

Superior and inferior oblique are slacked, visual axis is aligned with axis of pull for superior and inferior rectus muscles Tests lateral rectus muscles

What are the thickened fibrous bands that give eyelids some structure?

Superior and inferior tarsal plates (Tarsal glands on deep surface keep eyelids from sticking, when blocked a chalazion, crusty structure, develops)

What happens in CN IV (trochlear nerve) palsy?

Superior oblique msucle is paralyzed - *eye is stuck in up and in* and extorted position at resting gaze due to unopposed superior rectus and inferior oblique muscles Patient often tilts head away from affected side to compensate for loss of intorsion Eye wont rotate, whole head rotates to align eyes

What does superior division of oculomotor nerve (CN III) innervate?

Superior rectus and levator palpebrae superioris msucles

What is the muscle responsible for "wide-eyed" sympathetic response

Superior tarsal muscle (in purple) Smooth muscle - sympathetic Responsible for resting elevation of upper eyelid and full contraction (wide-eyed sympathetic response)

What are the openings on the rim of the orbit?

Supraorbital foramen/notch (frontal) infraorbital foramen (maxilla)

How is lens anchored to ciliary process?

Suspensory/zonular fibers

two muscles which insert into the upper eyelid to elevate it

- levator palpeerde superioris M - skeletal muscle - superior tarsal M - smooth muscle

3 layers of the eye

- outer fibrous: sclera + cornea - inner: deepest, retina - vascular: choroid, ciliary body, iris

short ciliary nerve

- pass through ciliary ganglion (COPS) to pierce sclera - carry postgang. sympathetics AND postgang. parasympathetics to eye for smooth muscle in the eye

What is the degree of deviation of the orbital axis from the visual axis

23 degrees

What is the bony orbit of the eye shaped like?

4-sided pyramid at orbital rim with posteromedial apex at optic canal

retinal ganglion cell axons gather at the optic disk to form...

optic nerve (no photoreceptors here creates a blind spot, and is also the point where the central artery and vein of retina branch into the eye

muscle for active closing of the eye

orbicularis oculi M - is a sphincter for blinking and squinting *eyelids close passively due to elastic recoil

orbital vs. visual axis

orbital: axis of structures within the orbit visual: where the eyes are actually pointed

Where do the eyelids meet?

palpebral fissure (eyelashes are near the fissure)

Where does infratrochlear nerve travel and supply?

red It is an anterior continuation of nasociliary; supplies upper eyelid, bridge of nose

What maintains binocular visual field when the head is tilted?

rotation of eyes

What will cause exopthalmos?

"Bulging eyes" Thyroid disease (Graves' disease)

nerves of the orbit

CN II, III, IV, V1, VI, sympathetic fibers

sclera

"white of the eye"; covers posterior 5/6 of the eye. Continuous with dura mater at optic nerve (thus tough, fibrous opaque)

What does lacrimal artery supply?

(Dark blue) Lacrimal gland

What does central artery of retina pierce/supply?

(Green) Pierces optic nerve, enters eye through optic disk, only blood supply to neural portion of retina (important for photoreceptors of the eye itself)

What does ciliary artery pierce/supply?

(Orange) Pierces sclera to supply eyeball

What does ant/post ethmoidal arteries pierce and supply?

(Pink) Pierce medial wall to supply ethmoidal air cells and some nasal cavity

What does supraorbital artery pass though/supply?

(Teal) Passes through supraorbital notch/foramen to supply central forehead

describe the Levator palpebrae superioris muscle

(superior division of CN III) Skeletal muscle Posterior origin above optic canal on lesser wing of sphenoid, inserts into skin of upper eyelid and superior tarsal plate

Light passes through which 4 reactive structures on the way to the back of the eye?

- cornea - aqueous humor - lens - vitreous body

What does nasociliary branch into?

- Ant/posterior ethmoidal nerve (purple) - Infratrochlear nerve (red) - Long ciliary (pink) - Short ciliary (blue)

Where does opthalamic artery branch from and what does it travel with into optic canal?

- Branches from internal carotid artery - Follows optic nerve through optic canal into orbit via optic canal - supplies eye and supporting structures, some face, some nasal cavity (Pictured in yellow)

long ciliary nerve

- sensory from eyeball - carry postganglionic sympathetics to dilator papillae muscles

Where does lacrimal gland empty to?

1. Empty through ducts into superior conjunctival fornix- wiped by action of orbicularis oculi muscle lateral to medial across surface of eye towards lacrimal lake at medial canthus (corner) 2. Puncta on medial corners of eyelids drain through lacrimal canaliculi into lacrimal sac in lacrimal fossa 3. fluid drains inferiorly through nasolacrimal duct to empty into inferior nasal meatus in nasal cavity Then through nasalacrimal duct to empty into inferior nasal meatus in nasal cavity

What are the 3 main layers of inner neural layer and what do they do?

1. Photoreceptors (rods and cones) - primary light transducing cells 2. Bipolar layer - relay cells between photoreceptors and retinal ganglion cells 3. Retinal ganglion cell layer - axons of these cells form optic nerve

What are the major veins draining the orbit and where do they go to?

1. Superior and inferior opthalamic veins (blue) - drain orbital structures and communicate with veins of forehead and face (pass through superior orbital fissure to drain into cavernous sinus, inferior can drain to pterygoid plexus in infratemporal fossa) 2. Central vein of retina (green) - drains retina into cavernous sinus

two divisions of oculomotor nerve

1. superior division: levator palpeerde superioris + superior rectus 2. inferior division: medial recuts m, inferior rectus m, inferior oblique m, carries pregang. PSNS fibers

What supplies vision?

CN II

Where is lateral rectus muscle located and what does it do?

Along deep lateral wall of orbit Abducts away from nose Innervated by CN VI (abducens)

Where is the medial rectus muscle located and what action does it do?

Along deep wall of orbit, inferior to superior oblique muscle Adducts pupil towards nose Innervated by inferior division of CN III

What do the medial and lateral palpebral ligaments do?

Anchor tarsi to orbital rim

Where the inferior oblique muscle located?

Anterior origin at inferior medial corner of bony rim, inserts across eye onto posterolateral portion

What is the clear, watery part of the eye that nourishes cornea and lens?

Aqueous humor (red)

What does the lens do?

Biconvex transparent structure with an elastic capsule; adjustments in shape changes the refraction angle, allowing fine adjustments for focus *anchored to ciliary processes via zonular fibers

macular degeneration

Breakdown of central vision due to atrophy or over-vascularization of macula

Describe the parasympathetic supply from inferior division of CN III

Carries preganglionic parasympaethic fibers from Edinger Westphal nucleus in midbrain Synapse at ciliary ganglion (positioned on lateral side of optic nerve, suspended by fibers from nasociliary nerve) Postganglionic parasympaethic fibers travel on short ciliary nerves into eye, supply sphincter papillae and ciliary muscles

What is accommodation?

Changes in shape of lens to adjust focal point, especially for close vision (distant vision is resting state for eyes)

What composes the vascular layer of the eye?

Choroid Ciliary body - ciliary process and aqueous humor Iris

What anchors the lens?

Ciliary processes - via suspensory/zonular fibers Also produces aqueous humor

What is the iris?

Circular, fibromuscular aperture on anterior surface of lens Central pupil changes diameter to regulate amount of light entering the eye

What happens in the pupillary reflex?

Consensual constriction of iris in response to increase in light input

What does the ciliary body contain?

Contains smooth muscles that regulate tension on and shape of the lens - ciliary processes anchor lens via suspesnory/zonular fibers and produce aqueous humor

What happens in optic chiasm lesion (pituitary adenoma)?

Damage to fibers crossing from nasal retina of both eyes = loss of temporal visual field in both eyes but sparing of nasal visual field (tunnel vision) Normal pupillary reflex (biolateral projection for consensual reflex) Bitemporal hemianopsia

What happens in optic tract lesion (stroke)?

Damage to fibers from contralateral half of visual field from both eyes Lesion to left optic tract = loss of right half of both visual fields Normal pupillary reflex (bilateral projection from consensual reflex) Same sided hemianopsia

What does the outer pigmented layer of the retina do?

Dark brown, absorbs light that passes through neural layer to prevent backscatter over photoreceptors

Where is inferior rectus located and what is its action?

Deep along floor of orbit Primarily depresses pupil but also adducts and extorts (pull is medial to axis of rotation) Rolls eyeball "down and in" Innervated by inferior division of CN III

Where is superior rectus muscle located and what is its action?

Deep to levator palpebrae superioris M Complex action - primarily elevates pupil but also adducts and intorts (pull is medial to axis of rotation) Rolls eyeball "up and in" Innervated by superior division of CN III

What is the action of the superior oblique muscle?

Depresses, abducts and intorts pupil Combined action = roll eyeball down and out by pulling back of eye medially and anteriorly from above

what is the action of the superior oblique muscles?

Depresses, abducts, introits pupil - "down and out"

Where do the 2 oblique muscles insert on the eye? What are their actions?

Do not attach at common tednidnous ring, insert towards back of eye (posterior to axis of rotation), pulls medially and anteriorly Primary rotators of the eye (intorsion/extorision) - superior and inferior oblique muscles

Rectus vs oblique extra ocular muscles

Four rectus mm: insert toward front of the eye and pull straight along orbital axis Two oblique mm: insert towards back of eye, pulling forward and medially

What is the parasympathetic stimulation that allows for accommodation?

From edinger-westphal nucleus via inferior division of CN III to ciliary ganglion through short ciliary nerves Causes ciliary muscles to bulge inward which relieves tension on zonular fibers and allows elastic lens capsule to become more rounded for close vision

Where does oculomotor nerve travel to supply the eye

From oculomotor nucleus in midbrain, divides into superior and inferior divisions as it enters orbit through superior orbital fissure and common tendinous ring Superior division passes SUPERIOR to optic nerve - innervates superior rectus M and levator palpebrae superioris M Inferior passes INFERIOR to optic nerve - innervates medial rectus, inferior rectus, and inferior oblique muscle

What composes the roof of the orbit?

Frontal (teal) and posteriorly by lesser wing of sphenoid (yellow)

What happens in a blowout fracture?

Impact trauma to side of orbit is robust and transfers force to weaker parts of the orbit. Traumatic collapse of orbital floor (very thin bone) - blood, fluid, orbital contents (fat, inferior rectus muscle) enter maxillary sinus - can damage infraorbital nerve due to passage through infraorbital groove/canal - sesnory loss to infraorbital position of face/anterior upper teeth - potential entrapment/inflammation of inferior eye

Where are the 1st order cell bodies for the sesnory limb of the corneal reflex nerves (long and short ciliary nerves) located?

In trigeminal ganglion

What happens with blockage of aqueous humor?

Increases intraocular pressure = glaucoma Can cause blindness due to compression of optic nerve or retinal vasculature

What is inferior oblique muscle innervated by?

Inferior division CN III

What is inferior rectus innervated by?

Inferior division of CN III

What is the only muscle that can ELEVATE pupil from an ADDUCTED position?

Inferior oblique muscle

What are the openings in the inferior/floor of the orbit?

Inferior orbital fissure (sphenoid/maxilla) infraorbital groove/canal (maxilla)

What do optic tracts contain?

Ipsilateral temporal retina and contralateral nasal retina (continues towards brain from optic chiasm) Left optic tract = projections from right halves of both visual fields Right optic tract = projections from left halves of both visual fields

Where does CN IV (trochlear nerve) travel and what does it innervate?

It comes from trochlear nucleus in pons, enters orbit through superior orbital fissure outside of common tendinous ring and *innervates superior oblique mscule* (Trochlar nerve supplies muscle with a trochlea)

What do puncta on medial corners of eyelids drain through?

Lacrimal canaliculi into lacrimal sac in lacrimal fossa

What are the openings in the medial of the orbit?

Lacrimal fossa (lacrimal/maxilla) - heads to nasolacrimal canal; collection structure drains tears to nasal cavity anterior and posterior ethmoidal foramina (ethmoid) - neurovasculature to nasal cavity

What keeps eyelashes from sticking

Large ciliary glands These get blocked = stye

What happens in CN VI (abducens) palsy?

Lateral rectus is paralyzed - *affected eye cannot abduct* Strabismus at resting gaze - medial rectus muscle is unopposed on affected side, pulls pupil medially (results in horizontal diplopia - double vision)

What does inferior division of oculomotor nerve (CN III) innervate?

Medial rectus, inferior rectus and inferior oblique muscles *also carries preganglionic parasympathetic fibers (from edinger-Westphalia nucleus in midbrain), synapse at ciliary ganglion, post travel on short ciliary into eye to supply sphincter papillae and ciliary muscles

What composes the floor of the orbit?

Mostly maxilla (red), zygomatic makes rim (grayish blue), and posteriorly by tip of palatine (purple) *also very thin - serves as roof of maxillary sinus; prone to failure with impact trauma to skull

What composes the lateral wall of the orbit?

Mostly zygomatic (grayish blue) and posteriorly by greater wing of sphenoid (yellow) *very robust, anchor for temporalis fascia, must resist mechanical strain

What does CN V1 branch into?

NFL (medial —> lateral) Nasociliary Frontal Lacrimal

Do axons from temporal retina cross?

No. Project ipsilaterally

What happens in CN III (oculomotor) palsy?

Paralysis of several msucles: superior inferior and medial rectus, inferior oblique, levator palpebrae superioris Only functional extraocular muscles are superior oblique and lateral rectus: Pull affected eye into severely down and out position at resting gaze, ptosis from loss of levator palpebrae superioris Dilation of affected pupil - paralysis of sphincter pupillae muscle from loss of parasympathetic (unbalanced dilator papillae msucle - sympathetic)

What is the muscle present in lower eyelid?

Only orbicularis oculi muscle

Light from objects passes through pupil onto ......

Opposite side of retina (Nasal projects to temporal part of retina and vice versa)

what are the arteries supplying the orbit?

Opthalamic (yellow) Central artery of retina (green) Ciliary (orange) Lacrimal (blue) Supraorbital (teal) Ant/post ethmoidal (pink)

What are the openings on the posterior orbit?

Optic canal - for optic nerve and ophthalmic artery superior orbital fissure (sphenoid)

Where do axons from nasal retina (temporal visual field) cross to contralateral side?

Optic chiasm (Located anterior to pituitary infundibulum and medial to internal carotid arteries)

Describe sensory limb of pupillary reflex

Optic nerve carries it - retina fibers split at optic chiasm towards both optic tracts (bilateral projection) Small portion of fibers project to ipsilateral pretectal nucleus in midbrain Pretectal fibers project bilaterally to edinger-westphal nuclei which sends parasympaethic fibers to ipsilateral CN III to sphincter papillae muscles in iris to constrict pupil Bilateral projection from pretectal nuclei produce consensual motor response even if only 1 eye is stimulated

What do lateral geniculate nucleus fibers form?

Optic radiations which project to ipsilateral visual cortex in occipital lobe Because of crossed fibers at optic chiasm, each visual cortex has portions of visual field from both eyes. Allows for processing and comparison for depth perception

What is the skeletal muscle responsible for blinking, squinting and protection of eye exterior and what is its innervation?

Orbicularis oculi muscle (deep to the skin) Innervated by CN VII

Where is the superior oblique muscle located?

Origin medial to optic canal on lesser wing of sphenoid, belly found in supramedial part of orbit but tendon is redirected onto eye by fibrous trochlea Inserts posteriorly and laterally at back of sclera

What are the 2 layers of the retina?

Outer pigmented layer (dark brown) inner neural layer

What does paralysis of superior tarsal muscle result in?

Ptosis/drooping of eyelid (horners syndrome)

Where is the lacrimal gland located and what does it do?

Postioned in supralateral corner of the orbit - secretes lacrimal fluid (tears)

Extraocular muscles are innervated ________ and on their _____surface

Proximally and on their inner surface

What is the choroid?

Reddish brown major vascular network between retina and sclera - supplies outer retina

What is the innermost layer of the eye

Retina

What is located in the inner layer of the eye?

Retina - outer pigmented layer, continues onto iris and absorbs light - inner photosensitive layer

What do rods and cones do?

Rods = sensitive to low light but not color specific, found mostly in peripheral retina Cones = sensitve to parts of color spectrum and much sharper acuity, concentrated in macula at posterior retina

What is the conjunctiva and what are the parts of it?

Specialized, vascular epithelium that lubricates inner surface of eyelid and external surface of eye. Forms closed conjunctival sac when eyelids close (contains lacrimal fluid) Palpebral conjunctiva - lines inner surface of eyelids Bulbar conjunctiva - lines exposed parts of sclera, ends at corneal limbus where it blends with thin epithelium of cornea Superior/inferior conjunctival fornices - junction of palpebral and bulbar conjunctiva

What muscles control pupil size and what is their innervation?

Sphincter pupillae muscle (parasympathetic) - constrict pupil Dilator pupillae muscle (sympathetic) - contract/dialate pupil (when running from a bear you need to see)

What is the blinking response of the corneal reflex in response to?

Stimulation of nerve fibers on external eye - especially cornea (Reflexes always have sensory and motor component, thus testing reflex can isolate lesions to sensory or motor pathways)

Where do the majority of optic tract fibers project?

To ipsilateral lateral geniculate nucleus (LGN) of thalamus

What happens in an optic nerve lesion? (Glaucoma)

Total blindness in ipsilateral eye, no effect on contralateral eye Bilateral absence of pupillary reflex when affected eye is stimulated (loss of sensory limb) but normal consensual reflex when unaffected eye is sitmulated (motor limb intact)

What is the periorbita?

Tough membrane enclosing all orbital contents, continuous with periosteal layer of dura matter

Where does CN VI (abducens) travel and what does it supply?

Travels from abducens nucleus in pons and enters orbit through superior orbital fissure and common tendinous ring Supplies lateral rectus msucle (abducens nerve abducts)

Where does frontal nerve travel and what are its branches?

Travels just deep to Periorbita, superficial to levator palpebrae superioris muscle - most superficial structure in orbit Branches: Supratrochlear nerve (red) Supraorbital nerve (blue)

Where does lacrimal nerve travel and what does it carry?

Travels lateral in orbit superior to lateral rectus muscle, passes through lacrimal gland to supply skin of Supra lateral orbit Carries postganglionic parasympathetic fibers from pterygopalatine ganglion (CN VII) to lacrimal gland

How does CN V1 enter orbit

Via superior orbital fissue

What is the transparent gel-like structure in a collagen matrix that fills most of the eye?

Vitreous body Supports lens and retina (Eye floaters = loose clumps of collagen drifting around vitreous body)

base and apex of the bony orbit

base: orbital rim (outer margin) apex: optic canal (apex like in a pyramid - canal is not straight, but instead deviated)

supratrochlear nerve

branch of frontal supplies medial forehead

supraorbital nerve

branch of frontal supplies much of forehead and scalp

PSNS ganglion associated with the eye

ciliary ganglion (COPS)

Area of sharpest vision

fovea centralis - central depression of macula

What is the only muscle that can DEPRESS pupil from an ABDUCTED position?

inferior rectus muscle

extorsion

lateral rotation of the pupil

area which contains the deepest concentration of cones

macula lutea - just lateral to the optic disk and is in-line with visual axis

intorsion

medial rotation of the pupil

describe the placement of the medial and lateral walls in the orbit

medial walls are parasagittal lateral walls form 90 degree angle to one another *gives overall triangle shape

What is the only muscle that can DEPRESS pupil from an ADDUCTED position?

superior oblique muscle

What is the only muscle that can ELEVATE pupil from an ABDUCTED position?

superior rectus muscle

What is the sensory limb of the corneal reflex

via long and short ciliary nerves (CN V1: 1st order cell bodies in trigeminal ganglion) They travel in spinal trigeminal tract to synapse at spinal trigeminal nucleus (structure the extends from upper spinal cord to pons) 2nd order neurons project bilaterally to facial motor nuclei and superior salivary nuclei in pons (consensual response - both eyes blink when one is stimulated)

What is a consensual response?

when both eyes blink when one is stimulated - they react together