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Ocular Physiology > The Orbit > Flashcards

The Orbit Flashcards

1
Q

How many bones make up the boney orbit’s 4 walls? What are they?

A
  1. Sphenoid, frontal, zygomatic, ethmoid, lacrimal, palatine, and maxillary.
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2
Q

Which part of the orbital rim is thick and rounded and is protected from trauma?

A

Anterior aperture.

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3
Q

The strongest portion of the orbital rim is?

A

Lateral wall. (The zygomatic bone + zygomatic process of the frontal bone).

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4
Q

What is the tradeoff of the lateral orbital rim?

A

Strongest portion that’s a posteriorly directed concavity which allows for strong visual field but makes eye prone to injury.

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5
Q

The triangular shape of the orbital roof is formed by what two bones?

A

Frontal bone and the lesser wing of sphenoid bone (posterior to frontal).

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6
Q

The lacrimal fossa (fossa for the lacrimal gland) is found where?

A

Antero-lateral angle

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7
Q

Which part of the orbital rim is the weakest and thin and mainly consists of the orbital plate of the maxillary bone?

A

Orbital floor.

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8
Q

What is the main purpose of the orbital floor?

A

Gives support to the eye and adnexal tissues and separates them from the maxillary sinus.

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9
Q

How long is the orbital floor?

A

35-40 mm long.

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10
Q

True or False: The orbital floor does not extend to the apex.

A

True.

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11
Q

What happens during a blow-out fracture? What are some problems patient’s experience with this fracture?

A

The orbital floor blows out into the maxillary sinus providing protection to the eye and tissue. Loss of vision, diplopia, enophthalmos (eyeball sucked inwards), numb cheek.

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12
Q

What two bones form the lateral orbital wall?

A

Zygomatic bone anteriorly and greater wing of sphenoid bone posteriorly.

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13
Q

Which part of the rim is the smallest and thin?

A

Medial orbital wall.

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14
Q

Why is the medial wall less likely to fracture then any other part of the rim?

A

Lamina Papyracea of the Ethmoid Bone (extremely thin but uniformly supported by the honeycombed structure of the ethmoid sinus body lamina) is what helped medial wall from fracturing.

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15
Q

Which wall is fractured most often?

A

Floor.

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16
Q

What protects the medial wall from being fractured?

A

Lamina papyracea (honeycombed structure).

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17
Q

At birth, what is the diameter of the globe from posterior to anterior?

A

16 mm.

18
Q

The globe reaches 90% of its adult size when an infant is how old?

A

20 months.

19
Q

At adulthood, the anteroposterior diameter of the globe is?

A

24 mm. (But varies with gender, ethnicity, and refractive error).

20
Q

What is the volume of the globe?

A

7 cm^3.

21
Q

What is the volume of the orbit?

A

30 cm^3.

22
Q

What is the vertical diameter of the globe?

A

23 mm.

23
Q

What is the horizontal diameter of the globe?

A

23.5 mm.

24
Q

What is the anteroposterior diameter of the globe?

A

24 mm.

25
Q

What is Enophthalmos?

A

Inward displacement of the globe.

26
Q

What is Exophthalmos?

A

Forward displacement of the globe.

27
Q

The only place the orbit can acutely expand is which direction?

A

Anteriorly.

28
Q

The forward displacement of any object, not specific to the eye, is called what?

A

Proptosis.

29
Q

Thyroid Eye Disease is the most common cause of what?

A

Exophthalmos.

30
Q

What happens in the eye that causes Thyroid Eye disease?

A

GAG’s accumulate in the EOMs and/or connective tissue and fat and lead to swelling.

31
Q

What are other causes of exophthalmos?

A
  • Hemangiomas
  • Inflammatory pseudotumors
  • Benign and malignant tumors
  • craniostenoses and the craniofacial dysostosis.
32
Q

True or False: Enophthalmos may lead to pseudoexophthalmos of the contralateral eye.

A

True.

33
Q

In exophthalmos eye, will patient most likely be hyperopic in that eye or myopic?

A

Myopic. Eye bulged out.

34
Q

How is protrusion measured?

A

From the deepest part of the lateral rim to the corneal apex.

35
Q

Orbital connective tissue consist of what?

A

Fibroblasts and endothelial cells, collagen type I, III, IV.

36
Q

What is the purpose of collagen type I connective tissue?

A

Structural integrity.

37
Q

What is the purpose of collagen type III connective tissue?

A

Adhesion between connective tissue and adipocytes.

38
Q

What is the purpose of collagen type IV connective tissue?

A

Basement membranes of connective tissue vessels.

39
Q

What artery provides the primary blood supply to the orbit?

A

Ophthalmic artery.

40
Q

True or False: Orbital veins parallel orbital arteries.

A

Fails. Do not parallel.

41
Q

Do orbital veins possess valves?

A

No.

Ocular Physiology (6 decks)

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