The Orbit Flashcards

1
Q

What bones make up the bony structure of the orbital cavity?

A
  1. Palatine bone
  2. Ethmoid bone
  3. Lacrimal bone
  4. Maxilla
  5. Zygomatic Bone
  6. Frontal bone
  7. Sphenoid bone (greater wing)
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2
Q

What are the layers of the eyelid?

A
  1. Skin
  2. Subcutaneous tissue
  3. Orbicularis oculi muscle
  4. oribital septum
  5. Conjunctiva
  6. Tarus
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3
Q

What do we need to remember about the skin and subcutaneous tissue?

A

These are a thin layer, and the subcutaneous tissue acts as a potential space. With a skull fracture → raccoon eyes

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4
Q

What do we need to remember about the Oribicularis Oculi muscle

A

This is a two-part voluntary muscle, that extends outside the orbital cavity

  1. Palpebral Part: of the eyelids
  2. Orbital: Around the eye

Seals the orbital cavity, and is innervated by the facial nerve

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5
Q

What is the orbital septum

A

A continuation of the periosteal dural layer, running within the upper and lower eyelid

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6
Q

What are the muscles that control the tarsus raise of the eyelid and what innervates them? What happens if you get a loss of function?

A

The Levator palpebral superioris muscle (LPS) and the superior tarsal muscle (ST) ((a smooth muscle)).

LPS ⇔ occulamotor nerve

ST ⇔ postganglionic sympathetic fibres from the superior cervical ganglion

  • *Loss of function → ptosis (drooping)**
  • complete (LPS) or partial (ST)*
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7
Q

What do the tarsus glands secrete

A

They sit in the tarsus and secrete an oily substance, for protective lubrication

**a septum runs through the tarsus to stabilise it.

If the septum clogs → ‘chalazion’ bump on the eyelid (usually painless)

Don’t confuse with a painful sty which is an infected sweat gland!

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8
Q

What is the conjuctiva and what can go wrong?

A

The thin conjuctiva membrane covers the eyelid, avoids damage and scratching on eye.

Conjuctivitis is just an infection of this

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9
Q

What’s the innervation of the eyelid?

A

First division of the trigeminal = Upper lid

Second division of the trigeminal (maxillary) = lower lid

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10
Q

What’s the contents of the orbital cavity?

A
  • Eyeball
  • Extrinsic muscles of the eyeball
  • Lacrimal apparatus
  • Neurovascular structures
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11
Q

What are the extrinsic muscles of the eye?

A

Superior rectus
Inferior rectus
Medial rectus
Lateral rectus
Superior oblique
Medial oblique

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12
Q

Although in the orbit theres only one periosteal dura kayer the ‘periorbita’, where the cranial nerve enters the orbit there is ____

A

A seal made of both the periosteal and meningeal layer

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13
Q

The seal around the cranial Nerve is called the ________

A

Common tendinous ring (thickening of the periosteum).

Point of origin for all 4 rectus muscles, and many nerves run within this structire.

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14
Q

What runs in the oribital canal?

A
  1. Cranial Nerve II (Optic nerve)
  2. Ophthalmic artery
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15
Q

What runs in the superior orbital fissure?

A
  1. Superior ophthalmic vein
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16
Q

Whats in the lacrimal apparatus

A
  1. Lacrimal gland: on lateral side of orbit, hugging LPS, drains tears back to the eye
  2. Lacrimal canaliculi
  3. Lacrimal sac
  4. Nasolacrimal duct

Puncta: a pump that drains tears from lacrimal canaliculi → lacrimal sac → nasolacrimal duct → nose (*why you get a runny nose when you cry!!)

17
Q

Whats the main arterial supply of the orbit

A

The Ophthalmic artery through the optic canal, has lots of branches that go to different areas.

If you lose these arteries you will go blind

18
Q

Whats the main venous supply of the orbit?

A

Ophthalmic Vein, which communicates with the cavernous sinus and the facial nerves. THis is therefore where infection may drain to the brain, the ‘danger triangle’

19
Q

Although nearly everything is innervated by the occulomotor nerve CN III, what extrinsic muscles aren’t?

A
  1. Lateral Rectus: CN 6
  2. Superior Oblique: CN 4
20
Q

So what parts of the oculomotor nerve supply what?

A

Superior branch: Levator palpebrae superioris, superior rectus

Inferior Branch: Medial rectus, inferior rectus, inferior oblique, ciliary ganglion

You can figure out where the fracture is dependent on what symptoms?

21
Q

Superior Oblique origin, innervation

A

Innerevate by CN IV (trochlear), Doesn’t attach to the common tendonous ring, and its two bellies strangely comes medially, and then has a ‘pulley’ which allows it to pull the eye in/down.

Therefore a fracture on the medial side may damage the pulley attachment.

22
Q

What does the Ophthalmic Nerve (CN V1) innervate?

A

Branches:

Lacrimal Nerve → lacrimal gland
Frontal Nerve → sensory supply to frontal face
Nasociliary Nerve → Lacrimal duct/sac and nasal cavity

23
Q

The dogma of the dangerous triangle is that it is devoid of valves, hence can cause the spread infection. What is the truth?

A

in 75% specimens, valves were found in the superior veins, and non in the inferior.

Therefore superior ophthalmic, angular and supraoribital veins are NOT devoid of veins!

The Real Issue: there is a direct connection between veins, and the cavernous sinus.