Gross Anatomy And Development Of He Orbit And Eye Flashcards
What are the boney margins of the orbit?
Boney margins of the orbit:
• frontal, maxilla, zygomatic
Walls:
• frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal, palatine
What are the contents of the superior or ital fissure?
Superior orbital fissure
- CN III, IV, V1, VI, superior ophthalmic v.
What are the contents of the inferior orbital fissure?
Inferior orbital fissure
- V2, zygomatic nerve, inferior ophthalmic v., infraorbital a. and v.
What are the contents of the optic canal?
Optic canal
- CN II, ophthalmic a.
What are the contents of the nasolacrimal canal?
Nasolacrimal duct from lacrimal
fossa to nasal cavity (inferior
meatus)
Explain the development if the eye
- The eyes originally develop as a diverticulum of the forebrain neural tube
- The hollow diverticulum becomes the optic stalk and near surface ectoderm forms the optic cup
- Invagination process of optic cup extends into the ventral part of optic stalk to form a fissure called the retinal fissure
- Inside the fissure will run the hyaloid a. which will supply the internal structures of the eye
- Fissure normally closes around artery around the 6th week of development
- Hyaloid artery will eventually become the central retinal a.
explain the development if the opticc nerve
The axons from the ganglion cells of the retina grow towards the brain in the inner layer of optic stalk
-The optic nerve develops from the optic stalk
• The proximal part of hyaloid vessels get closed within optic nerve to form the central retinal a. & v.
How do Sclera and Cornea develop?
- Sclera and choroid develop from mesenchyme tissue surrounding the optic cup
- Cornea develops from:
- Corneal epithelium - from skin ectoderm
- Fibrous stroma - from the mesodermal capsule covering the optic cup
- Corneal endothelium - from the neural crest cells of optic cup
• The eyelids develop from skin folds filled with mesenchyme
How does the iris develop?
The iris develops from the rim of the optic cup
• Ciliary body develops from the optic cup (smooth muscle from mesenchyme)
- The hyaloid vessels supply the lens till 6th month of fetal life, after which the artery obliterates (lens becomes avascular). The remaining hyaloid artery becomes the central artery of the retina
- Eyelids remain adherent to each other till the 26th week
What is keyhole pupil?
Coloboma of the iris “keyhole pupil”
- Results due to incomplete closure of the retinal fissure
- Defect can extend to the ciliary body and retina
Describe the development of the retina
• The retina develops from the layers of the optic cup
- pigment layer of retina from the outer layer of
optic cup
- neural layer of the retina from the inner layer of
optic cup
• The cavity of the cup (intraretinal space) obliterates as the 2 layers fuse
Explain the detachment of the retina
The intra-retinal space provides an easy plane of cleavage for detachment of the retina
The detachment occurs between the neural and pigment layers of the retina
Detachment can occur secondarily during development or after birth as a result of a blow on the eye
Explain the development if the lens
Lens develops from the lens vesicle (surface ectoderm)
• The anterior wall of the lens vesicle becomes the sub- capsular lens epithelium
- The epithelial cells in the posterior wall lose their nuclei and elongate forming primary lens fibers (transparent) which fill the cavity of the lens vesicle
- Secondary lens fibers, cuboidal, from the equatorial region, overlap the primary fibers – increasing the lens diameter as it grows
What is cataracts?
- Opaqueness of the lens giving the eye a grayish white appearance
- May be congenital due to teratogenic agents or infections during pregnancy (especially between 4th-7th week when the lens is forming) or occur later in life due to normal aging, trauma, radiation etc.
- Can be removed surgically as outpatient procedure under local anesthesi
Whats the flow of tears?
Canaliculi drain into lacrimal sac which is continuous with nasolacrimal duct
• Nasolacrimal duct empties into inferior meatus of nasal cavity
Describe the innervation of the conjuctiva
• Palpebral conjunctiva lines each eyelid
- Sensory innervation:
• upper lid – CN V1
• lower lid – CN V2
• Bulbar conjunctiva lines the sclera, but not cornea of eye
- Sensory innervation - CN V1
What are extraocular (extrinsic eye muscles)?
• 4 rectus muscles; superior (SR), inferior (IR), medial (MR), lateral (LR) - origin: common tendinous ring
• Superior oblique (SO)
- origin: bony wall of orbit posteriorly
• Inferior oblique (IO)
- origin: anteroinferior aspect of orbit medially
• Lavator palpebrae superioris (LPS)
- origin: bony wall of orbit posteriorly
• Distal attachments: sclera for all muscles except
LPS (tarsal plate)
Summarize eye muscle innervation
Superior oblique m. (SO) by trochlear n. (CN lV)
Lateral rectus m. (LR) by abducens n. (CN Vl)
All other extraocular muscles and LPS by oculomotor n. (CN lll)
(SO4 LR6)3
Diiscuss the optic vs visual axis
Orbital axis is fixed- long axis of orbit
Visual axis is variable- according to where eye is looking
What is the main eye test?
Muscle Testing - H Test
Muscle testing differs from muscle actions due to attempt to isolate specific muscles
Patient looks
Out then up- superior rectus
Out then down- inferior rectus
Out- lateral rectus
In -Medial rectus
In then up- internal oblique
In then down- in then down
What are the arteries in the orbit?
Central a. of retina
• enters optic n. to supply
visual layer of retina
Ethmoidal aa.
• to nasal cavity/paranasal
sinuses
Posterior ciliary aa.
• to pigmented layer of retina
Muscular branches
• To extraocular muscles
Lacrimal a.
• to lacrimal gland
Supraorbital/Supratrochlear aa.
• to anterior scalp
What are the veins in orbit?
- Sup. and inf. ophthalmic vv. join and exit via sup. orbital fissure to empty into cavernous sinus (may stay separate and exit via sup. and inf. orbital fissure respectively)
- Inf. ophthalmic vein can drain into (or receive blood from) the pterygoid plexus
- Sup. ophthalmic vein can receive blood from angular, supratrochlear, and supraorbital veins
- Ophthalmic vv. provide connection between facial vv. and cavernous sinus
- Potential route for infection
What is the function of the lacrimal nerve?
Lacrimal nerve:
• Receives branch from zygomaticotemporal nerve which carries post ganglionic parasympathetic fibers to the lacrimal gland
• Sensory to lacrimal gland, lateral parts of the conjunctiva and lateral part of upper eyelid
What are the components of the frontal nerve?
Frontal nerve
• Supratrochlear
– Sensory to the conjunctiva, the skin of the upper eyelid and forehead
• Supraorbital
– Sensory to the conjunctiva, upper eyelid, forehead and scalp up to the middle of the scalp
What are the components of Nasocilliary nerve?
Nasociliary nerve
• Long ciliary
– Sensory to eyeball and contains post ganglion sympathetics for pupillary dilation
• Posterior ethmoidal
– Sensory to the posterior ethmoidal cells and sphenoid sinus
• Anterior ethmoidal
– Sensory to the anterior cranial fossa, parts of nasal cavity and skin of central lower parts of nose
• Infratrochlear
– Medial parts of upper and lower eyelids, skin of upper part of nose
Explain Glaucoma
Glaucoma (high ocular pressure)
Open angle: angle between iris and cornea is open; uveoskleral drainage intact but trabecular meshwork becomes slowly blocked and interferes with drainage; iris in normal position Closed angle: uveoscleral drainage and trabecular meshwork blocked; iris against cornea
What is Chalazion?
Chalazion = Meibomian gland becomes inflamed/blocked; usually not painful; further back from eyelid edge Stye = hordeolum; infected eyelash root, painful (Sty = pig pen) Blepharitis = base of eyelashes red and swollen
Swelling of the parotid salivary gland due to viral or bacterial infection, tumor, autoimmune condition.
Duct opens in oral vestibule opposite maxillary molar 2
CN VII travels through the parotid gland
What is Horner syndrome?
Horner syndrome (severed sympathetics anywhere between T1 and up): pseudo-ptosis, constricted pupil CN III lesion (including parasympathetics): complete ptosis, pupil dilated, eye looks down and out)
UMN/LMN lesion of facial nerve: see image (which one affects the eye most?)
What are the intracranial venous connections?
Emissary veins
‣ Connect extracranial veins with intracranial veins
Facial vein communicates with deeper veins: ‣ Ophthalmic veins ‣ Infra-orbital vein ‣ Pterygoid plexus of veins ‣ Cavernous sinus
All provide a possible route of entry for infections from face and scalp to deep intracranial venous structures
