Anatomy of the Eye and Orbit
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Questions and Answers

The orbital fascia is continuous with the pia mater at the back of the orbit.

False (B)

Accessory ocular structures include the extraocular muscles, eyelids, conjunctiva and the salivary gland.

False (B)

Orbital fat volume fluctuates significantly with changes in the amount of general body fat and fluid.

False (B)

The orbit is a bony cavity shaped like a pyramid with its apex located at the front of the facial skeleton.

<p>False (B)</p> Signup and view all the answers

The roof of the orbit is mainly composed of the greater wing of the sphenoid bone.

<p>False (B)</p> Signup and view all the answers

The medial wall of the orbit, extending from front to back, measures approximately 10 cm in length.

<p>False (B)</p> Signup and view all the answers

The posterior lacrimal crest is a vertical ridge located on the ethmoid bone.

<p>False (B)</p> Signup and view all the answers

The fossa for the lacrimal sac is situated posteriorly to the posterior lacrimal crest.

<p>False (B)</p> Signup and view all the answers

The inferior rectus muscle tendon is inserted into the superior surface of the sclera anterior to the coronal equator of the eye.

<p>False (B)</p> Signup and view all the answers

The trochlea is a loop of dense fibrous tissue attached to the frontal bone.

<p>True (A)</p> Signup and view all the answers

The lateral rectus is unique because its origin is described as C-shaped.

<p>True (A)</p> Signup and view all the answers

The superior oblique muscle passes through the trochlea and is inserted into the posterosuperior quadrant of the sclera.

<p>True (A)</p> Signup and view all the answers

LR6S0403 is a mnemonic for the nerve supply of the superior rectus muscle by the fourth cranial nerve.

<p>False (B)</p> Signup and view all the answers

The skin of the lower eyelid is supplied by the infraorbital nerve.

<p>True (A)</p> Signup and view all the answers

The conjunctiva is loosely attached over the posterior part of the sclera.

<p>False (B)</p> Signup and view all the answers

The palpebral part of the lacrimal gland is supported by the medial edge of the aponeurotic tendon of levator palpebrae superioris.

<p>False (B)</p> Signup and view all the answers

The cornea is innervated by the lacrimal nerve.

<p>False (B)</p> Signup and view all the answers

Blinking is primarily caused by the palpebral fibers of orbicularis oculi.

<p>True (A)</p> Signup and view all the answers

The lacrimal sac serves as an emergency apparatus for removing excessive tears.

<p>True (A)</p> Signup and view all the answers

The upper eyelid is opened by the contraction of the corrugator supercilii.

<p>False (B)</p> Signup and view all the answers

The lacrimal gland has both an orbital and a palpebral part.

<p>True (A)</p> Signup and view all the answers

The oily layer of the tear film is produced by sebaceous glands of the lids and caruncle.

<p>True (A)</p> Signup and view all the answers

The plica semilunaris is comparable to the nictitating membrane found in some animals.

<p>True (A)</p> Signup and view all the answers

The anterior and posterior ethmoidal foramina are located at the intersection of the medial wall and the floor of the orbit.

<p>False (B)</p> Signup and view all the answers

The lateral wall of the orbit is primarily composed of the zygomatic bone and the lesser wing of the sphenoid.

<p>False (B)</p> Signup and view all the answers

The inferior orbital fissure connects the orbit with the pterygopalatine and infratemporal fossae.

<p>True (A)</p> Signup and view all the answers

If extended posteriorly, the lateral walls of the orbits would intersect in the hypophysial fossa.

<p>True (A)</p> Signup and view all the answers

The orbital process of the temporal bone contributes to the floor of the orbit.

<p>False (B)</p> Signup and view all the answers

The supraorbital margin is formed by the frontal bone and features a notch or canal for the supraorbital nerve and artery.

<p>True (A)</p> Signup and view all the answers

The infraorbital margin is formed exclusively by the maxilla.

<p>False (B)</p> Signup and view all the answers

The medial margin of the orbit is defined by the posterior lacrimal crest.

<p>False (B)</p> Signup and view all the answers

The tarsal plates, responsible for maintaining the shape of the eyelids, are composed of cartilage.

<p>False (B)</p> Signup and view all the answers

The lacrimal punctum, located at the medial end of each eyelid margin, drains excess tears into the lacrimal canaliculus.

<p>True (A)</p> Signup and view all the answers

The lacrimal sac has a thick wall and an internal diameter of 3.5 mm.

<p>False (B)</p> Signup and view all the answers

The levator palpebrae superioris muscle is responsible for moving the upper eyelid.

<p>True (A)</p> Signup and view all the answers

The extraocular muscles of the eye include six muscles.

<p>True (A)</p> Signup and view all the answers

The lacrimal, frontal, and trochlear nerves pass through the tendinous ring.

<p>False (B)</p> Signup and view all the answers

The mucous membrane of the nasolacrimal duct contains folds that serve as valves.

<p>True (A)</p> Signup and view all the answers

Blinking helps to pump the lacrimal fluid into the nose through the nasolacrimal duct.

<p>True (A)</p> Signup and view all the answers

The lateral walls of the orbits are parallel to each other.

<p>False (B)</p> Signup and view all the answers

The superior rectus muscle inserts into the upper part of the sclera anterior to the coronal equator of the eye.

<p>True (A)</p> Signup and view all the answers

The optic nerve and ocular muscles originate from the back of the lateral wall of the orbit.

<p>False (B)</p> Signup and view all the answers

Facial nerve paralysis leads to complete ptosis of the eyelids.

<p>False (B)</p> Signup and view all the answers

Flashcards

Orbit

The bony cavity in the front of the skull that holds the eye and accessory structures.

Accessory ocular structures

Includes the extraocular muscles, eyelids, conjunctiva, and lacrimal gland that support eye function.

Extraocular muscles

Muscles that move the eye and help in its positioning.

Orbital fascia

The periosteum of the orbit that connects to the dura mater and optic nerve sheath.

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Orbital fat

Fat that fills spaces in the orbit and cushions the eye.

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Medial wall of the orbit

The wall that connects to the frontal process of the maxilla and contains the lacrimal structures.

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Lacrimal gland

Part of the lacrimal apparatus that produces tears.

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Nasolacrimal canal

The channel that drains tears from the lacrimal sac to the nasal cavity.

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Ethmoidal Foramina

Openings for nerves and vessels located between the medial wall and roof of the orbit.

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Optic Canal

A passage in the sphenoid bone for the optic nerve and ophthalmic artery.

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Orbital Plate of Ethmoid

Thin bone forming part of the medial wall of the orbit, separating the orbit from the nasal cavity.

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Inferior Orbital Fissure

A gap that separates the lateral wall from the floor of the orbit, leading to the pterygopalatine fossa.

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Tarsal Plates

Rigid fibrous structures that give shape to the eyelids and anchor eyelashes.

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Palpebral Fissure

The opening between the eyelids through which light passes.

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Lacrimal Papilla

Small elevation at the edge of eyelids containing openings for tear drainage.

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Orbital Septum

Fibrous structure that surrounds and supports the eyelids, connecting to the anterior lacrimal crest.

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Supraorbital Foramen

An opening in the frontal bone that allows passage for the supraorbital nerve and artery.

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Zygomatic Bone

Bone that forms the prominence of the cheek and part of the lateral wall of the orbit.

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Lacrimal sac

A reservoir that holds tears before they drain through the nasolacrimal duct.

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Nasolacrimal duct

A duct that carries tears from the lacrimal sac to the nasal cavity.

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Muscles of the orbit

Muscles surrounding the eye that control its movement.

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Rectus muscles

Four muscles that move the eye up, down, left, and right.

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Oblique muscles

Two muscles that control rotational movements of the eye.

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Levator palpebrae superioris

A muscle that elevates the upper eyelid.

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Superior orbital fissure

An opening in the skull through which nerves and muscles enter the orbit.

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Oculomotor nerve

A cranial nerve responsible for eye movement and pupil constriction.

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Ptosis

Drooping of the upper eyelid due to muscle weakness or nerve damage.

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Adduction of the eye

Movement of the eye medially towards the nose.

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Nerve supply to upper lid

Upper lid is supplied by lacrimal, supraorbital, supratrochlear, and infratrochlear nerves.

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Nerve supply to lower lid

Lower lid receives input from the infraorbital nerve.

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Mobility of eyelids

Upper lid has great mobility; lower lid has little mobility.

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Conjunctiva

A transparent membrane covering the eyelids and sclera, providing lubrication.

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Lacrimal apparatus

System responsible for producing and draining tears, including the lacrimal gland and sac.

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Tear film layers

Three layers: oily, aqueous, and mucus; protects the cornea.

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Blinking reflex

Automatic response to keep the eye moist or drain excessive tears.

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Role of eyelids

Close to protect and open to expose the eye, facilitating tear distribution.

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Lacrimal canaliculi

Channels that carry tears from puncta to the lacrimal sac.

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Inferior Rectus Muscle

A muscle that arises from the lower part of the tendinous ring and inserts into the inferior surface of the sclera.

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Lateral Rectus Muscle

A muscle that originates from the lateral convexity of the tendinous ring and inserts into the lateral surface of the sclera.

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Superior Oblique Muscle

A muscle that arises from the sphenoid and passes through the trochlea before inserting into the sclera.

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Trochlea

A fibrous loop that acts as a pulley for the tendons of the superior oblique muscle.

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Nerve Supplies for Eye Muscles

LR6SO4O3: signifies the lateral rectus is supplied by the 6th nerve, superior oblique by the 4th, and other muscles by the 3rd nerve.

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Study Notes

Orbit and Eye

  • The eye (eyeball) is the organ of vision, part of the visual apparatus.
  • The orbit is a bony cavity shaped like a pyramid in the front of the skull.
  • Orbital fascia, continuous with dura mater and optic nerve sheath, surrounds the orbit.
  • Extraocular muscles move the eye, eyelids, conjunctiva, and lacrimal gland are accessory structures situated within the orbit.
  • Orbital fat provides cushioning for the optic nerve and eye.

Orbit

  • The orbit's shape is a pyramid tilted, with apex at the back and base forming the opening (aditus) on the facial skeleton.
  • The roof is the orbital part of the frontal bone and lesser wing of sphenoid.
  • The medial wall extends from anterior lacrimal crest on maxilla, across lacrimal bone and orbital plate of ethmoid to body of sphenoid and optic canal; notable features include lacrimal fossa and anterior/posterior ethmoidal foramina.
  • The lateral wall consists of zygomatic bone (marginal tubercle), greater wing of sphenoid. Gaps include superior and inferior orbital fissures leading to cranial fossae.
  • The floor of the orbit is the orbital surface of the maxilla completed by zygomatic bone laterally and orbital process of palatine bone posteriorly.
  • The orbital margin has four curved sides (supraorbital, lateral, infraorbital, medial), each with specific structures like foramina and notches for nerves and blood vessels.

Eyelids

  • Eyelids consist of loose skin in front and conjunctiva behind.

  • The orbital septum forms the framework of eyelids, thickened into tarsal plates.

  • Orbicularis oculi muscle lies in front of the septum.

  • The orbital septum, attached to anterior lacrimal crest and orbital margins, has a palpebral fissure (buttonhole gap).

  • Superior and inferior tarsal plates are thickenings of the orbital septum.

  • Tarsal plates are formed of dense fibrous tissue, not cartilage.

  • Medial and lateral palpebral ligaments attach tarsal plates to anterior lacrimal crest.

  • Palpebral part of orbicularis oculi curves in front of tarsal plates and orbital septum; angular vein and facial artery terminal branch are superficial.

  • Eyelashes are long hairs attached to tarsal plates.

  • Tarsal plates are crescent-shaped, rigid, dense fibrous tissue, curved to the eye's curve.

  • Meibomian glands in tarsal plates produce an oil to waterproof lid margins, preventing evaporation of tears on cornea.

  • A lacrimal papilla and punctum open into canals to remove excess tears.

  • Blood supply is by palpebral branches of ophthalmic artery; nerve supply comes from lacrimal, supraorbital, supratrochlear, infratrochlear, and infraorbital nerves.

Conjunctiva

  • A transparent membrane blends with cornea at margins and is loosely attached to sclera, reflecting to inner eyelid surfaces.
  • Conjunctiva is attached to tarsal plates; continuous with skin at lid margins.
  • A plica semilunaris fold at medial canthus; might be homologous to some animals' third eyelid.
  • Fornix folds allow lateral corneal deviation.
  • Lacrimal canaliculi and sac prevent infolding at medial canthus.
  • Caruncle (modified skin) and lacus lacrimalis, area of accumulation for excess tears

Lacrimal Apparatus

  • The lacrimal apparatus produces and removes tears, composed of lacrimal gland, canaliculi, sac, and duct.
  • Lacrimal gland, serous gland with orbital and palpebral parts, lies in lacrimal fossa
  • Secretomotor fibers from superior salivary nucleus reach the gland via the greater petrosal, pterygopalatine, and zygomatic nerves.
  • Tears are produced to replace evaporation loss, spread across eye during eye closure.
  • Excessive tears are removed by lacrimal sac and nasolacrimal duct.
  • Lacrimal canaliculi, tiny canals, convey tears to the lacrimal sac.
  • Lacrimal sac lies in fossa of maxilla and lacrimal bone.
  • Nasolacrimal duct (2 cm long) opens into inferior meatus; acts like a rubber syringe with a oneway valve system, pumping excess tears into nasal cavity.

Muscles of the Orbit

  • Six extraocular muscles move the eye

  • Superior, inferior, medial and lateral rectus muscles.

  • Superior & inferior oblique muscles

  • Levator palpebrae superioris muscle (elevates the upper eyelid).

  • Orbitalis muscle (present in animals with few variations)

  • Eye position in orbit is not symmetrical; eyes face forward, parallel, and optic nerve and ocular muscles travel to lateral attachments.

  • Tendinous ring surrounds optic foramen; four recti muscles originate in the ring/ surrounding bone tissue.

  • Levator palpebrae superioris and superior oblique originate above the ring.

  • Various nerves pass through the superior orbital fissure, affecting eye function.

  • Muscles (rectus & obliques) cause eye movement (adduction, turn in/out/up/down)

  • Levator palpebrae superioris opens the eye by elevating upper eyelid.

  • Nerve supplies are key for muscle actions and function.

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Description

This quiz covers the anatomy of the eye and its surrounding structures, including the orbit. It focuses on the characteristics, functions, and details of the orbital cavity and its components. Test your knowledge on the intricate relationships and structures that contribute to vision.

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