Anatomy of the Orbit Flashcards

1
Q

List the bones that form the orbit?

A
  • Frontal
  • Sphenoid
  • Lacrimal
  • Maxillary
  • Ethmoid
  • Zygomatic
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2
Q

3 foramina at the back of the orbit?

A
  • Optic foramina
  • Superior orbital fissure
  • inferior orbital fissure
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3
Q

Why are the medial wall and floor of the orbit weaker than the rim/other walls?

A

Because they are closely associated to paranasal air sinuses - only separated by a thin wall

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4
Q

The eyeball itself is about 24mm long and the orbit is about 40mm long. What occupies the majority of this extra space?
Function?

A

Orbital fat

Mainly functions as a cushion

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5
Q

What are the conjunctiva? Function?

A

The mucosal lining of the inner eyelid, also covers the sclera

Changes from skin to conjunctiva at margin of eyelid

Helps lubricate the eye by producing mucus and tears, also performs immune surveillance preventing microbes from invading the eye

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6
Q

What is the name of the muscle that raises the top eyelid? Origin and insertion?

A

levator palpebrae superioris

Originates on the lesser wing of the sphenoid bone, inserts on the tarsal plate of the eyelid

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7
Q

What gives structure to the eyelids?

What is it composed of?

A

The tarsal plate

Dense connective tissue

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8
Q

What is the name of the glands associated with the tarsal plate? What do they secrete?

A

Meibomian glands

Secrete meibum, an oily substance that prevents evaporation of the eyes tear film

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9
Q

Where are the conjuctiva located?

A
  • Begins at the margin of the eyelid
  • Continues along the eyelid and then loops back around to cover the sclera (area where it turns around called fornix)
  • Covers the sclera, stops at cornea (doesn’t cover cornea)
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10
Q

How does conjunctivitis present?

A

When the conjunctiva become inflamed the blood vessels of the usually transparent layer over the eye dilate

So the eye appears red

Also: itching & watery eyes

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11
Q

What is the nerve that supplies parasympathetic innervation to the lacrimal gland?

A

Facial nerve (CN VII)

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12
Q

Where does the lacrimal gland drain into?

A

Lacrimal duct

The superior fornix of the conjunctiva

eye

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13
Q

Describe the passage of tears from the lacrimal gland

A

Lacrimal gland -> lacrimal duct -> surface of eyeball -> lacrimal punctum -> lacrimal canaliculi -> lacrimal sac -> nasolacrimal duct -> inferior meatus of nasal cavity -> absorbed in nasopharynx

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14
Q

How does blinking promote the movement of tears into the lacrimal sac?

A

Since the orbicularis oculi muscles are over the lacrimal sac, blinking opens the sac and creates a negative pressure situation - drawing fluid into the sac

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15
Q

What is the function of the intrinsic muscles of the eye? Of the extrinsic?

A

Intrinsic - Control pupil diameter and lens curvature

Extrinsic - move the eye

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16
Q

What is the muscle responsible for lens accommodation? Where is it located?
Innervation?

A

Ciliaris muscle

Located in the ciliary body

CN III - oculomotor n.

17
Q

What are the muscles that control pupil diameter?

A

Constrictor pupillae and dilator pupillae

18
Q

What are the 6 extrinsic muscles of the eye? Fibre orientation for each?

A

Straight fibres from posterior:
- Superior, Inferior, Medial and Lateral RECTUS

Obliquely attached:
- Superior and inferior oblique muscles

19
Q

Describe the innervation of the extrinsic muscles of the eye

A

SO4 LR6 - rest 3

  • Trochlear (IV) supples superior oblique
  • Abducent (VI) supplies Lateral rectus
  • All others: oculomotor n. (III)
20
Q

What are the cranial nerves that supply the orbit?

How do these nerves enter the orbit?

A
  • Optic (II)
  • Oculomotor (III)
  • Trochlear (IV)
  • Abducent (VI)

Enter through the superior orbital fissure, Except for optic which goes through the optic foramen
- Trigeminal V1 & V2 (V1 SOF, V2 IOF)

21
Q

Which branches of the trigeminal nerve supply the orbit?

A

Opthalmic and Maxillary

  • V1 (opthalmic) through SOF
  • V2 (maxillary) through IOF
22
Q

Which artery supplies blood to the orbit? Which carotid is it a branch of?

A
  • Opthalmic artery

Branch of internal carotid

23
Q

Which artery supplies the inner layers of the retina? How does it get to the retina?
Which artery is it a branch of?

A

Central retinal artery - travels within the optic nerve to get to the retina (accompanied by vein)

Branch of opthalmic artery

24
Q

What is the optic disc?

A

Head of the optic nerve on the retina, physiological blind spot

25
Q

What investigation can let you see inside of the eye?

A

Opthalmoscopy / Fundoscopy

26
Q

How is the fundus of the eye segmented?

A

Divided into 4 segments, named based on whether they’re closer to nasal or temporal sided. Centre of the segments is the optic disc

  • Lower nasal and temporal quadrants
  • Upper nasal and temporal quadrants
27
Q

Which veins drain the eye and orbit?

What do they drain into?

A

Superior and inferior opthalmic veins

Drain into the cavernous sinus (right behind the orbit)

go through the SOF

28
Q

What do the intracranial venous sinuses lie between?

What do the sinuses collectively drain into?

A

The two layers of the dura mater

Drain into the internal jugular veins on each side