Anatomy/Embryo of Orbit and Eye Flashcards
orbit intro
each orbit is shaped like a qaud. pyramid with base facing antero-laterally
- medial orbital walls are parallel to each other, lateral walls are perp. to each other
which bones contribute to bony orbit?
- frontal
- maxilla
- sphenoid
- lacrimal
- ethmoid
- palatine
- zygomatic
base:
orbital margin: frontal, zygomatic, maxilla bones
- provides protection
roof
frontal bone and some sphenoid bone
- has fossa for lacrimal gland
floor
maxilla
zygomatic
palatine
medial wall
ethomoid
lacrimal bone
maxilla
- lacrimal fossa; houses the medial portion of the lacrimal system
lateral wall
zygomatic
sphenoid
know the foramina that pass through here
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blowout fractures
- fracture of orbital walls (usually inferior or medial)
- damage to floor: involves maxillary sinus; intraocular fat/bleeding can spread to maxillary sinus
- inferior rectus mm. often gets trapped; causing diplopia
- enopthalamos: movment of fat into surrounding spaces of msucle entrapment (sinking in of the eye)
- damage to medial wall: usually involves sphnoidal and ethmoidal air sinuses
- damage to roof can involve anterior cranial fossa
- globe can be damaged causing detached retina and bleeding
orbital tumors
malignant tumors originating in the sphenoidal and ethmoidal sinuses, middle cranial , and infratemporal fossa can erode through the thin walls of the orbit or pass directly through foramina.
- tumors compress the orbital contents
- can cause exopthalamos
what fascia lines the orbit?
periorbital fascia
- continuous with periosteal dura at optic canal and superior orbital fissure
- continuous with muscular fascias of eye muscles
what fascia surrounds the eyeball?
fascial sheath of eyeball - “Tenon’s Capsule” - thin membrane that is external to the sclera. Its continuous with muscular fascia of extraoc. eye mm. and separates eyeball from orbital fat.
orbital fat
provides cushion, lubrication and protection to the eye.
- during starvation the eyes become sunken in “enopthalmos” due to loss of this fat layer
palpebra
= “eyelids”
Five layer of the eyelid?
- skin
- loose CT
- muscle (orbicularis oculi and levator palpebrae superioris)
- Tarsal plate
- Palpebra conjunctiva
tarsal plate
dense ct for structural support of eyelid.
- orbital septum is fibrous membrane which connects tarsi to margins of orbit, contains orbital fat and helps limit spread of infections between face and orbit.
- medial palpebral ligament (connects tarsi to medial wall of orbit)
- lateral palpebral ligament
which glands are assocoiated with the eyelids?
- tarsal (Meibomian) glands (sebaceous glands)
- glands of zeis (smaller sebaveous glands)
- glands of moll (sweat glands)
- clinical correlation *
Meibomian cyst = chalazian = inflammation and obstruction of glands
hordeoum (cyst of eyelash glands)
orbicularis occuli
- sphincter mm. of eyelid
- CN VII
- ** CN VII impairement results in an eyelid that cannot close completely. inferior eyelid tends to fall away from eyeball and results in dryness and irritation of the cornea and sclera. (seen with Bell’s Palsy)
Levator Palpebrae superioris (LPS)
O: lesser wing of sphenoid
I: skin of superior eyelid
A: elevates superior eyelid
N: CN III
Note: superior portion of LPS attaches to superior tarsal plate and is sympathetically innfervated
Loss of CN III or sympathetic lesion?
Causes ptosis (inability to open upper eyelid) due to loss of LPS
Horner’s syndrome
loss of sympathetic innervation to head
- patient presents with ptosis due to loss of superior tarsal portion of LPS
conjunctiva of the eye?
- palpebral conjunctiva = epithelium of internal eye
- bulbar conjunctiva = outer epithelium of sclera
- conjunctival sac: area b/w palpebral and bulbar conjunctiva; opens at palpebral fissure
- conjunctival fornices: superior and inferior points are formed where bulbar and palpebral conjunctiva are continuous
what is the flow of tears?
lacrimal gland –> conjunctival sac –> surface of eye –> lacrimal papillae with puncta –> cannaliculae –> lacrimal sac –> nasolacrimal duct
lacrimal gland
a. Compound tubuloalveolar gland
b. Located in lacrimal fossa in superolateral orbit.
c. Secretes lacrimal fluid – watery, serous secretion – into conjunctival sac.
d. Lacrimal fluid keeps sclera and cornea moist and contains an antibacterial agent for protection.
lacrimal cannaliculi
located in medial angle of eye
- begins at lacrimal punctum opening into the lacrimal papilla
lacrimal sac
receives fluid from lacrimal cannaliculi
what is external fibrous tunic of eye composed of?
- Sclera: tough fibrous layer covering posterior globe
2. Cornea: avascular transparent layer that provides most of eyes refractile capabilities. has many pain receptors
corneal neovascularization
abnormal process where blood vessels grow into corneal stroma secondary to hypoxic damage
choroid
vascular, loose CT located deep to sclera. provides vascular supply to fibrous layers and outermost retina. contains melanocytes which produce melanin to absorb photons of light
Iris: what are its two mm?
Central aperture that forms the pupil; controls amount of light entering pupil
- sphincter pupillae: reduces diameter of pupil (miosis) to decrease light enter eye. PS via CN III
- dilator pupillae - increases diameter (mydriasis) to increase light entering eye. Symp innervation.
Ciliary body
- ciliary processes: finger-like extensions which secrete aqueous humor into posterior chamber. suspensory ligaments (zonule fibers) connect ciliary processes to lens.
- ciliary muscle
Ciliary muscle
PS innervation via CN III (lens round to focus near)
Accomodation!!! controls lens thickness via suspensory ligaments.
- -when looking at distant objects, the ciliary m. is relaxed and there is tension on the suspensory ligaments of lens. the ciliary processes pull on the lens and cause it to be stretched and thinned.
- -when focusing on near objects, the ciliary m. contracts. the ciliary m. pulls the ciliary body medially and anteriorly and reduces tension on suspensory ligaments. lesss tension on suspensory ligaments means that the lens becomes rounded and thicker.
- if there is no stimulation: lens is thin, flat, and focus on distance
what are two main fn. of ciliary body?
produce aqeous humor
accomodation
inner neural tunic
- visual receptor portion of retina: contains rods and cones, ganglion cells which form the optic n.
ora serrata
anterior termination of the retina
optic disc
blind spot - located in posterior pole of globe. site where CN II and central retinal artery and vein enter globe. no photoreceptive cells.
macula lutea
yellow-pigmented zone lateral to optic disc
fovea centralis
oval depression located in teh central of the macula. site of greatest visual acuity due to density of cones
what is blood supply of retina
- central retinal aa. supplies neural portion (not rods/cones)
- choroid vessels supply pigmented epithelium and rod/cone layer
retinal detachment
occurs when the pigmented epithelium separates from the underlying rods and cones layer. Detachment can cause blindness if not corrected immediately due to loss of metabolic support and blood supply to rods and cones.
Lens
transparent, retractile, flexible, biconvex disc located posterior to iris
* Refraction and Accomodation*
Clinical:
- presbyopia
- cataracts develop when the proteins of the lens aggregate, producing opaque lens
presbyopia
hardening (loss of elasticity) of the lens; inability to accomodate and focus on near objects
what are two aqeous chambers?
anterior: b/w cornea and iris
posterio: b/w iris and lens
what is aqueous humor
- refractive fluid, produced by ciliary processes in posterior chamber. flows from posterior chamber to anterior chamber via the pupil.
where does aqueous humor drain?
drains to venous system via the scleral venous sinus (Canal of schlemm) at the iridocorneal angle.
- the scleral venous sinus is covered by a trabecular meshwork which helps drain the humor
- scleral venous sinus drains to corticose and anterior ciliary vv.
Glaucoma
conditions caused by excess aqeous humor in chambers. most often due to decreased outflow of aqeous humor due to blockage of scleral venous sinus or from increased production of aqeous humor.
- results in increased intraoc. pressure and can cause blindness
vitreous body
between lens and posterior surface of eye. filled with vitreous humor (transparent, refractile jelly-like substance)
enopthalamos
retraction of eyeball into orbit - seen in starvation
what is the optic vesicle “cup” formed from?
evagination from forebrain neuroectoderm: from diencephalon
- opticl vesicles invaginate on themselves to form double-walled optic cup.
- optic cup retains connection to forebrain at optic stalk
- choroid fissure forms on ventral surface of optic cup (carries hyaloid vessels).
- ** ultimately forms retina and optic nerve ***
what forms the lens?
surface ectoderm : lens placode –> lens vesicle –> lens
what do two layers of optic cup form/
outer layer = pigmented layer of retina
inner layer = neural layer of retina
* n. fibers from retina migrate through the choroid fissure to form CN II (7th week choroid fissure closes)
congenital retinal detachment
occurs when inner and outer layer of optic cup fail to fuse, results in separation of pigmented and neural layers of retina and will cause blindness if not reattached.
how is choroid developed?
from vascular layer of mesenchyme surrounding optic cup
how is iris and ciliary body developed?
- outer portion is derived from vascular mesenchyme surrounding optic cup.
- inner portion is derived from optic cup (no neural invovement)
- melanocytes migrate into iris about 6-10 mos of age
iridopupillary membrane
vascular structure that normallly seperates the ant/post/ chambers, degenerates around week 15.
- failure to degenerate leads to congenital atresia of pupil
coloboma
results from a failure of choroid fissure to fuse during 7th week - may also involve the retina
how are sclera and cornear derived
from fibrous layer of mesenchyme surrounding optic cup
how do aqeous and vitreous chambers of eye form/
the chambers form in areas of cell death.
how is lens derived? clinical correlation?
derived from lens vesicle
congenital aphakia: agenesis of lens
how do extrinsic eye mm. form?
form from mesoderm of myotomes
what artery supplies the orbit/eyeball?
opthalmic artery (arises from internal carotid a.) - enters orbit via optic canal
what are branches of opthalic artery?
- central retinal a. (pierces optic sheath and runs with optic n to supply retina - except rods/cones/pigmented eptihelium layers)
- short psoterior ciliary: pierce sclera near optic n. to supply choroid
- long posterior ciliary: pierce sclera anteriorly to supply ciliary body/iris.
- anterior ciliary aa: arise from muscular branches; to ciliary body/iris
- lacrimal: to lacrimal gland and lateral portions of eyelids
- supraorbital: to forehead and scalp
- posterior ethmoidal
- anterior ethmoidal
- medial palpebral (eyelids)
- supratrochlear (to forehead and scalp)
- dorsal nasal (supplies dorsal surface of nose)
where do vv. of orbit and eyeball drain?
central vein usually drains to cavernous sinus directly.
- vorticose vv. drain the choroid, ciliary body and iris
- superior/inferior opthalmic vv. drain to cavernous sinus via opthalmic v.
thrombophlebitis
clot in cavernous sinus may move into central retinal vein which my lead to vision loss
increased intracranial pressure
optic n. central retinal a, and central retinal v. can be compressed and occluded:
- occlusion of central retinal v = papilledema (retinal edema)
- compression of optic n = blindness
- retinal a. occlusion = blindness b/c of loss of supply of blood to retina.
extortion vs. intortion
extortion = superior pole of eyeball rotating laterally
intorsion: superior pole of eyeball rotated medially
Medial rectus
adducts eye
CN III
(if eye is held in abduction, pointing out laterally, indicates loss of this muscle)
lateral rectus
abducts eyes
CN VI
(if eye is held in adduction, facing medially, indicates loss of this muscle)
superior rectus
elevates eye, adducts = intorsion (points eye diagnally and medially)
CN III
- weakness shown in inability to elevate eye when it is fully abducted
inferior rectus
depresses and adducts: intorsion
CN III
testing: weakness of depression, loss of depression when eye is fully abducted
if eye is held in abduction, loss of what muscle?
medial rectus, CNIII
if eye is held in adducted position?
loss of lateral rectus, CN VI
if eye is unable to elevate when it is fully abducted?
loss of superior rectus, CN III
if eye is unable to depress when fully abducted?
loss of inferior rectus, CN III
inferior oblique
elevates and abducts, extorsion
CN III
unable to elevate the eye when it is fully adducted?
loss of inferior oblique, CN III
superior oblique
depresses, abducts, intorsion
CN IV
loss of depression when eye is fully adducted?
superior oblique
CN IV
what does oculomotor nerve provide?
GSE and GVE-P fibers
- GSE: superior division: levator palpebrae superioris and superior rectus
- GSE: inferior division: medial rectus, inferior rectus, inferior oblique muscles
- GVE-P: inferior division- carries preganglionic PS fibers to ciliary ganglia
what are the nerves of the orbit?
sensory: GSA via V1
mvmt of eye: GSE via CN III, IV, VI
PS: GVE-P via CN III
mvmt of orbicularis oculi: SVE via CN VII
ptosis or complete closure of eye, diplopia, eye abducted and depressed, dilation of pupil, loss of accommodation seen with?
Oculomotor nerve palsy
- ptosis = loss of levator palpebrae superioris
- eye down and out: loss of all adducting and elevation muscles.
- dilation of pupil: loss of constriction via sphincter puillae (constriction due to PS innervation)
- loss of accomodation (b/c loss of ciliary m. via PS)
trochlear nerve
GSE for superior oblique muscle
diplopia, eye slightly elevated and adducted, loss of depression when eye is fully adducted
trochlear nerve palsy, loss of superior oblique mm.
diplopia and inability to move eye laterally
abducent nerve palsy
optic nerve
SSA: vision
- optic nerve is covered in meninges (dura, arachnoid, pia) - optic nerve fibers are axons of ganglion cell layer in retina which pass through optic disk and exit via the lamina cribrosa of sclera posteriorly
what are three branches of Opthalmic nerve in orbit?
CN V1= opthalmic nerve
- nasociliary
- frontal
- lacrimal
nasociliary branch of V1? what are its branches?
GSA- sensory root in the ciliary ganglia
- short ciliary nn: arise from ciliary ganglia on lateral side of optic n: carry Post symp, PS, sensory fibers
- long ciliary nn: arise from nasociliary n. on medial side of optic n; carry post symp and sensory fibers
- posterior ethmoidal nn: to ethmoidal air cells and dura
- anterior ethmoidal nn: to ethmoidal air cells, nasal cavity, dura, terminates as external nasal nerve
- infratrochlear n: exits orbit atmedial angle, sensory to skin at root of nose, eyelids, palpebral conjunctiva, lacrimal sac
what does frontal branch of V1 provide?
supratrochelar n, supraorbital n.
what does lacrimal branch of V1 provide?
- sensory to lacrimal gland; lateral portion of superior eyelid.
- carries postganglionic PS and symp to the lacrimal gland
how do you tell the difference between long and short ciliary nn?
both arise from nasociliary branch of V1:
long = medial of optic n.
short = lateral of optic n.
- both carry symp and sensory fibers. only short carry PS for innervation of ciliary m.
where is ciliary ganglion? what does it contain? what does it receive?
located b/w lateral rectus mm. and optic nerve
- contains postganglionic PS cell bodies
- synapse of CN III for PS control of pupillary sphincter m.
- receives three roots:
1. sensory root from nasociliary n.
2. PS motor root for oculomotor n.
3. Symp motor root from internal carotid plexus
Where are Parasympathetics of the intraocular eye mucslces located? what is their path? what do they innervate in intraocular eye?
innervate sphincter pupillae m. and ciliary mm.
- preganglionic cells are located in Edinger-Westphal nucleus
- fibers travel with CN III
- postganglionic cells located in ciliary ganglion
- postganglionic fibers distribute via short ciliary nn. to sphincter pupillae m. and ciliary m.
Where are sympathetics, what do they innervate in the intraocular eye mm?
innervate dilator pupillae and superior tarsal mm.
- preganglionic cells are located in upper thoracic spine levels (T1-2)
- fibers enter symp chain and ascend.
- postganglionic cells located in superior cervical symp ganglionc which travel with internal carotid plexus, which gives a sympathetic motor root to the ciliary ganglion.
- post fibers pass through ciliary ganglia without synapsing and distribute via long and short ciliary nn. to the dilator pupillae and superior tarsal m.
what is the autonomic PS innervation to lacrimal gland?
- pre cell bodies in salivatory nucleus
- travel with greater petrosal via CN VII
- post cell bodies in pterygopalatine ganglia
- post fibers travel with zygomatic (V2) and lacrimal (V1) nerves.
** fn: increases lacrimal gland secretion **
sympathetic innervation to the lacrimal gland?
- pre cell bodies: T1-4
- pre fibers: symp chain ascending
- post cell bodies: superior symp. ganglia, fibers distributed via carotid n (deep petrosal n.)
- greater and deep petrosal nn. merge to form nerve of pteyrgoid canal
- postganglionic nn. distribute with zygomatic (V2) and lacrimal (V1) nerves
** function: vasomotor; creates more watery lacrimal fluid ***
pupillary light reflex
fn: protect eye from excessive light exposure
1. affarent: CN II - shine light
2. efferent: CN III (GVE-P to sphincter pupillae m.) - both pupils constrict
corneal reflex
fn: protects eyes from foreign bodies
1. affarent n: CN V1 (general sensation of pain to eye)
2. Efferent n: CN VII (orbicularis oculi)- causes blink
- puff air on eye, stimiulating V1, causes both eyes to blink due to VII
- has both direct and consensual response
accomodation reflex
fn: viewing near objects
affarent: CN II, vision
efferent: CN III (GSE, GVE-P).
when looking rom a distant to a near object, CN II is stimulated. This causes a direct and consensual response and causes three things:
- ciliary mm. contract causing rounding of lens (accomodation) via CN III, GVE-P
- pupils constrict via constrictor pupillae m (CN III, GVE-P)
- eyes adduct, stimulated by CN III (GSE) via LR.
what will dysfunction in PS innervation to intraocular eye mm. look like?
- pupil will be dilated due to loss of PS innervation to sphincter pupillae
- presbyopia: inability to see near objects due to decreased PS innervation to ciliary mm. and decreased accommodation
miosis
constriction of pupil = PS
mydriasis
dilation of pupil = symp
what will dysfunction in sympathetics of intraoccular eye mm. show as?
- constricted pupil, loss of pupillary dilation due to dilator pupillae
- ptosis: due to loss of symp innervation to superior tarsal mm, which assists with elevation of upper eyelid
