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2 - HNA > The Orbit > Flashcards

The Orbit Flashcards

1
Q

Describe the orbit

A

Bony, cone shaped socket with its apex pointing posteromedially, consisting of 7 bones. It formed around the optic nerve and orb.

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2
Q

Bones of the orbit

A

7 bones:

  1. Frontal (orbital plate)
  2. Sphenoid (greater & lesser wings)
  3. Ethmoid bone (labyrinth)
  4. Lacrimal bone
  5. Palatine bone (orbital process)
  6. Maxilla (orbital plate)
  7. Zygomatic bone
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3
Q

Boundaries of the orbit

A
  • Roof: frontal bone
  • Floor: maxilla
  • Lateral wall: zygomatic bone & greater wing of the sphenoid
  • Medial wall: ethmoid bone
    • Lacrimal bone & frontal process of maxilla contribute anteriorly
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4
Q

Discuss the lacrimal fossa

A
  • Depression posterior to the inferomedial angle of the orbital rim
  • Houses the lacrimal sac
  • Below is a large foramen for nasolacrimal duct
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5
Q

What are the groups of muscles of the eye?

A
  1. Intraocular
  2. Extraocular which move the orb
  3. Extraocular which elevate the eyelid
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6
Q

Intraocular muscles of the eye

A
  • Ciliary muscle - change shape of the lens
  • Pupillary muscles - constrict/dilate pupil

Preganglionic parasympathetic fibres from III

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7
Q

Extraocular muscles which move the eye

A
  • Recti - tendinous ring → just anterior to equator, behind the junction between sclera & cornea
  • Obliques - insert just posterior to the equator

NB: any coordinated movements involve at least 3 muscles

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8
Q

Extraocular muscles acting on the eyelid

A

Levator palpebrae superioris - elevates upper eyelid

Mixed III/sympathetic innervation

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9
Q

Superior rectus

A

Elevates & adducts, III

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10
Q

Inferior rectus

A

Depressed & adducts, III

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11
Q

Medial rectus

A

Adducts, III

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12
Q

Lateral rectus

A

Abducts, VI

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13
Q

Superior oblique

A

Depresses & abducts, IV

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14
Q

Inferior oblique

A

Elevates & abducts, III

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15
Q

Blood supply to the orbit

A

Via branches of the ophthalmic artery (ICA):

  • Central artery of the retina
  • Branches to the extraocular muscles
  • Lacrimal artery
    • Gives recurrent meningeal branch with anastomoses with MMA

Pass through optic canal (ophthalmic & CAotR)

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16
Q

Venous drainage of the orbit

A
  • Superior ophthalmic vein → cavernous sinus
    • Via SOF
  • Inferior ophthalmic vein: 3 options
    1. Joins superior
    2. Passes through SOF → cavernous sinus
    3. Passes through IOF and joins pterygoid venous plexus
17
Q

Structures running through the orbital fissures (S→I)

A

SOF - outside of tendinous ring:

  • Superior ophthalmic vein
  • Lacrimal n. (Va)
  • Frontal n. (Va)
  • Trochlear n. (IV)

SOF - inside tendinous ring:

  • Superior division of III
  • Nasociliary n. (Va)
  • Inferior division of III
  • Abducent n. (VI)

IOF: inferior ophthalmic vein?

18
Q

Describe the eyelids

A
  • Movable folds which function to protect the eye
    • Canthi = angle between eyelids when open
    • Palpebral fissure = space between
  • Tarsal plates = condensed connective tissue
  • Superior plate is insertion for LPS
19
Q

Describe the tarsal glands

A
  • Modified sebaceous glands, produce an oily secretion
    • Make the lid margins waterproof
    • Decrease evaporation of tears from cornea
  • Open onto the skin posterior to the eyelashes
20
Q

Diagram: conjunctival sac

A
21
Q

Describe the location of the conjunctiva

A
  • Line inner aspect of the eyelids: palpebral
  • At root of eyelid reflect onto anterior aspect of the eyeball: bulbar
22
Q

Describe the lacrimal gland

A
  • Occupies a depression in the superolateral angle of the orbit
  • Its ducts drain into the lateral part of the superior conjunctival fornix
23
Q

Path of tears

A
  • Swept from blinking → lacrimal lake
  • Lake → lacrimal canaliculi → lacrimal sac → nasolacrimal duct → inferior meatus of nose

NB: opening of NL duct guarded by folds of mucous membrane preventing air being blown into the sac

2 - HNA (11 decks)

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