Anatomy Orbits Flashcards
Embryology of the eye
Neuroectoderm (retina, iris, optic nerve) Surface ectoderm (lens) Mesoderm (vascular structures, sclera, choroid)
Orbital bones:
Roof
Floor
Medial Wall
Lateral Wall
Roof: Frontal, Lesser wing sphenoid bone
Floor: Maxilla, Zygomatic bone
Medial Wall: Ethmoid bone (lamina papyracea), Lacrimal bone, Maxilla
Greater wing of sphenoid bone
Zygomatic bone
What is a blow out fracture?
CT findings?
Direct blow that results in increased intraorbital pressure
‘Trap door’ fragment
The inferior orbital rin has to be intact
Downward displacement of bone fragments
Inferior rectus m. involvement
Herniation of orbital fat into maxillary sinus
Air in the orbit -> fracture medial wall
Superior orbital fissure bones
Lesser and greater wings of the sphenoid bone
Inferior orbital fissure bones
Greater wing of sphenoid bone
Maxilla and palatine bone
Where is the optic canal located?
Orbital apex in the sphenoid bone
Superior orbital fissure contents
Cranial nerves III, IV, VI Lacrimal n. + frontal n. + nasociliary n. (opthalmic n) Orbital branch middle meningeal artery Recurrent branch lacrimal artery Super Ophth Vein Super Orbital vein
Mnemonic of the order in which the nerves pass through the superior orbital fissure
Lazy French Tarts Sit Naked In Anticipation
Lacrimal Frontal Trochlear Sup Div Oculomotor Nascociliary Infer Div Oculomotor Abducens
Inferior Orbital Fissure contents
Zygomatic n Parasympathetics for lacrimal gland Infraorbital art Infraorbital vein Infraorbital nerve Inferior opthalmic vein
Infraorbital sulcus and foramen contents
What is the importance of the infraorbital foramen?
Infraorbital artery, vein, nerve
Route for spread of infection or maxillary tumours to the orbit and skull base
Optic canal contents
Optic nerve, dural sheath
Ophthalmic artery
Central retinal vein
What structure is known as the septum?
The med. palpebral ligament
Intraconal lesions in the orbit
Melanoma, Metastasis, Retinoblastoma
Meningioma, Hemangioma, Optic glioma
Pseudotumor, Cellulitis, Graves disease
What is the origin of melanoma in the eye?
What is the location of melanoma in the orbit?
From the pigmented choroidal layer
Choroid >ciliary body >iris
What is the most common primary intraocular neoplasm in adults?
Melanoma
Complications of melanoma in the orbit
Retinal detachment and vitreous haemorrhage
What is dacryoadenitis?
What is the differential of dacryoadenitis?
Inflammation of the lacrimal gland
Preseptal or orbital cellulitis
What are the imaging findings of dacryoadenitis ?
Diffuse lacrimal enlargement
Poorly demarcated mass
NO bone destruction
What is chemosis of the eye?
Swelling of the tissue that lines the eyelids and surface of the eye (conjuctiva). Preseptal
What is scleritis ?
Chronic painful inflammatory disease of the sclera and episcleral tissues.
What is Bupthalmos ?
Which diseases are associated?
Enlargement of the globe due to increased intraocular pressure , secondary to obstruction of the Schlemm canal.
Sturge Weber
NF1
Cobblestone lissencephaly
What is coloboma?
Congenital fissure in the globe due to incomplete closure of the embryonic optic fissure.
What is staphyloma?
Protrusion of the uveal tissue through thinning of the sclera
What is the clinical finding in retinoblastoma?
- Leukoaria (white pupillary reflex) = cat eye reflex due to replacement of the vitreous humor by a white mass
- Reduced vision, eye pain, strabismus
What else can give a white eye?
Persistent hyperplastic primary vitreous
Bulb laceration
Extraocular muscles, action and nerves
Lat rectus - laterally - CN6
Med Rectus - medially - CN3
Sup Rectus - elevates turns medially - CN3
Inf. Rectus - depresses turns medially - CN3
Inf Oblique - elevates, turns laterally - CN3
Sup Oblique - depresses turns laterally - CN4
Branches of the Opthalmic artery
Central retinal artery
Posterior ciliary artery
Describe the orbital vein anastomosis creating a Danger zone
Facial vein ->angular vein -> SOV ->cavernous sinus
Facial vein > Infraorbital vein >pterygoid plexus >cavernous sinus
What is the Annulus of Zinn?
A fibrous ring formed by the common origin of the 4 rectus muscles
