Flashcards in The Orbit And The Eyeball Deck (35):
What is the angle between the two lateral walls?
Angle between the medial walls?
Angle between the optical axes? Which direction?
Which bones form the walls of the orbit?
Roof: frontal and sphenoid bone
Floor: maxilla, zygomatic and palatine
Medial: ethmoid, maxilla and lacrimal
Lateral: zygomatic and sphenoid
What marks the apex of the canal and what does it contain? Where is it located?
The optic canal which contains the optic nerve
Lesser wing of the sphenoid bone just medial to the superior orbital fissure
Which structures pass through the superior orbital fissure?
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Superior branch of oculomotor nerve
Inferior branch of oculomotor nerve
Where is there superior orbital fissure located?
Between greater and lesser wings of the sphenoid bone
Where is the inferior orbital fissure found?
Between the inferior and lateral walls of the orbit
Between maxilla and sphenoid
What passes through the inferior orbital fissure?
What is the optic nerve surrounded by and why?
Cranial meninges because it is an extension of the brain
What are the three layers of meninges?
Where does the optic nerve begin and end?
Retina of the eye to the primary visual cortex of the brain
How is the optic nerve formed?
Convergence of axons from the retinal ganglion cells which receive impulses from the photoreceptors of the eye (rods and cones)
What is the extracranial course of the optic nerve?
Leaves the bony orbit via the optic canal
Enters the cranial cavity along the surface of the middle cranial fossa (in close proximity to the pituitary gland)
What is the intracranial course of the optic nerve?
Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm
Here, fibres from the nasal (medial) half of each retina cross over, forming the optic tracts
Each tract travels to its corresponding hemisphere
What does each optic tract contain?
Left optic tract - fibres from left temporal (lateral) retina and right nasal (medial) retina
Right - fibres from right temporal retina and left nasal retina
How can a pituitary adenoma affect vision?
Pituitary gland is close to the optic chiasm
Compression particularly affects fibres which cross over from the nasal half of each retina.
If fibres which cross over from the nasal half of each retina are affected, what happens to vision?
Defect in the peripheral vision of both eyes - bitemporal hemianopia
How is the pituitary gland accessed?
Via sphenoid sinuses
Which walls are most likely to break in a blow to the eye?
Inferior and medial walls
What may a fracture of the medial wall involve?
Ethmoidal and sphenoidal sinuses
What can infraorbital bleeding cause from a fracture?
What is a blowout fracture?
Indirect traumatic injury that displaces the orbital walls
What are the medial walls of the orbit separated by?
The ethmoidal sinuses and the upper part of the nasal cavity
What complications can a blow out fracture lead to?
Muscle entrapment (inferior rectus)
What is the main blood supply to the orbit?
Ophthalmic artery, a branch of the internal carotid
Gives rise to the central artery of the retina which pierces the sheath of the optic nerve and runs with it, emerging at the optic disc
Which artery supplies the orbital floor?
Infraorbital artery, a branch of the external carotid
Blockage of which artery can cause blindness?
Venous drainage of the orbit?
Superior and inferior ophthalmic veins which exit through the superior orbital fissure and enter the cavernous sinus
Central vein of the retina which either enters the cavernous sinus directly or joins the ophthalmic vein
What can occlusion of these veins cause?
Slow, painless loss of vision
How can infection of the eye spread to the brain?
Via the veins
Which veins return aqueous humour to central circulation?
Scleral venous sinus which encircles the anterior chamber of the eyeball
What is the danger triangle of the face concerning infection?
Facial vein communicates with the cavernous sinus via the ophthalmic veins which is a possible route for spread of infection
What can cause infection in the cavernous sinus?
Cavernous sinus thrombosis