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Questions and Answers
What is the shape of the orbit?
What is the shape of the orbit?
Which bone forms the roof of the orbit?
Which bone forms the roof of the orbit?
What is the location of the lacrimal sac?
What is the location of the lacrimal sac?
What is the function of the lacrimal gland?
What is the function of the lacrimal gland?
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Which of the following structures is related to the orbit superiorly?
Which of the following structures is related to the orbit superiorly?
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What is the location of the Superior Orbital Fissure?
What is the location of the Superior Orbital Fissure?
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Which nerve supplies the lateral rectus muscle?
Which nerve supplies the lateral rectus muscle?
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What is the effect of parasympathetic activation on the pupil?
What is the effect of parasympathetic activation on the pupil?
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Through which fissure do the trochlear and abducens nerves enter the orbit?
Through which fissure do the trochlear and abducens nerves enter the orbit?
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What is the location of the ciliary ganglion?
What is the location of the ciliary ganglion?
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What is the result of sympathetic stimulation of the dilator pupillae muscle?
What is the result of sympathetic stimulation of the dilator pupillae muscle?
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Which artery supplies the retina?
Which artery supplies the retina?
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Which spinal segment is the origin of the sympathetic innervation of the orbit?
Which spinal segment is the origin of the sympathetic innervation of the orbit?
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What is the name of the syndrome that results from interruption of the sympathetic pathway at any level?
What is the name of the syndrome that results from interruption of the sympathetic pathway at any level?
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What is the effect of parasympathetic activation on the ciliary muscle?
What is the effect of parasympathetic activation on the ciliary muscle?
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Which visual field will cross over to the other side of the brain?
Which visual field will cross over to the other side of the brain?
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Which muscle is innervated by sympathetic fibers?
Which muscle is innervated by sympathetic fibers?
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Which vein is responsible for the main venous drainage of the orbit?
Which vein is responsible for the main venous drainage of the orbit?
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Which muscle is responsible for medial rotation and elevation of the eyeball?
Which muscle is responsible for medial rotation and elevation of the eyeball?
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Which nerve supplies the inferior oblique muscle?
Which nerve supplies the inferior oblique muscle?
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What is the action of the lateral rectus muscle?
What is the action of the lateral rectus muscle?
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Which part of the lacrimal apparatus collects tears from the eye?
Which part of the lacrimal apparatus collects tears from the eye?
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What is the action of the inferior rectus muscle?
What is the action of the inferior rectus muscle?
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Which muscle is responsible for lateral rotation and elevation of the eyeball?
Which muscle is responsible for lateral rotation and elevation of the eyeball?
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Which nerve supplies Muller’s muscle?
Which nerve supplies Muller’s muscle?
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What is the result of damage to the sympathetic supply (C1)?
What is the result of damage to the sympathetic supply (C1)?
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What type of epithelium is found on the sclera?
What type of epithelium is found on the sclera?
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Which nerve supplies the lower eyelid?
Which nerve supplies the lower eyelid?
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What is the function of the plica semilunaris?
What is the function of the plica semilunaris?
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Study Notes
Orbit and Associated Structures
- The orbit is a quadrangular, truncated cavity with a conical shape.
- The orbit has four boundaries:
- Superiorly: anterior cranial fossa
- Medially: nasal cavity
- Inferiorly: maxillary sinus
- Laterally: temporal fossa
Boundaries of the Orbit
- The medial wall consists of:
- Frontal bone
- Lacrimal bone
- Ethmoid bone
- The floor consists of:
- Maxilla
- Palatine bone
- The lateral wall consists of:
- Greater wing of sphenoid bone
- Zygomatic bone
- The roof consists of:
- Frontal bone (orbital plate)
- Lesser wing of sphenoid bone
Lacrimal Apparatus
- The lacrimal bone has a grooved area containing the lacrimal sac.
- The lacrimal bone has a shallow fossa for the lacrimal gland.
- The lacrimal apparatus consists of:
- Lacrimal gland
- Lacrimal puncta
- Lacrimal canaliculi
- Lacrimal sac
- The lacrimal gland is supplied by the oculomotor nerve.
Superior Orbital Fissure
- The superior orbital fissure is located at the apex of the orbit.
- The superior orbital fissure lies between the greater and lesser wings of the sphenoid bone.
- The inferior division of the oculomotor nerve sends a branch to the ciliary ganglion, carrying parasympathetic fibers.
Ciliary Ganglion
- The ciliary ganglion is a parasympathetic ganglion located near the orbital apex.
- The ciliary ganglion is situated between the optic nerve and the lateral rectus muscle.
- Preganglionic fibers travel via the inferior branch of the oculomotor nerve and relay in the ciliary ganglion.
- Postganglionic fibers pass through the short ciliary nerves and supply the sphincter pupillae and the ciliary muscle.
Nerves of the Orbit
- The trochlear nerve (CN IV) enters the orbit through the superior orbital fissure and supplies the superior oblique muscle.
- The abducens nerve (CN VI) enters the orbit through the superior orbital fissure and supplies the lateral rectus muscle.
- The oculomotor nerve (CN III) supplies:
- The inferior oblique muscle
- The inferior rectus muscle
- The medial rectus muscle
- The superior rectus muscle
- The levator palpebrae superioris muscle
Blood Supply of the Orbit
- The ophthalmic artery is a branch of the internal carotid artery.
- The ophthalmic artery enters the orbit through the optic canal along with the optic nerve.
- The branches of the ophthalmic artery are:
- Central artery of the retina
- Lacrimal artery
- Long and short ciliary arteries
- Supraorbital, ethmoidal, muscular, supratrochlear, and dorsal nasal arteries
Veins of the Orbit
- The venous drainage of the orbit is mainly through the superior ophthalmic vein.
- The superior ophthalmic vein is formed by the union of the angular vein and the supratrochlear vein.
Extraocular Muscles
- The extraocular muscles are:
- Lateral rectus muscle
- Medial rectus muscle
- Inferior rectus muscle
- Superior rectus muscle
- Inferior oblique muscle
- Superior oblique muscle
- The actions of the extraocular muscles are:
- Adduction (medial movement)
- Abduction (lateral movement)
- Elevation (superior movement)
- Depression (inferior movement)
- Medial rotation (intorsion)
- Lateral rotation (extorsion)
Eyelid
- The eyelid consists of five layers:
- Skin
- Subcutaneous tissue
- Muscle layer (orbicularis oculi)
- Tarsal plate
- Conjunctiva
- The conjunctiva lines the inner surface of the lid and is reflected at the fornices over the sclera.
- The conjunctiva is tightly bound to the underlying sclera.
- The epithelium of the conjunctiva varies from stratified squamous on the sclera to stratified columnar on the eyelid, studded with goblet cells.
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Description
Test your knowledge of the bony orbit, extra-ocular muscles, vessels, nerves, and lacrimal apparatus. Learn about the anatomy of the eye and its associated structures. Understand the functions and nerve supply of the muscles of the eyeball.
