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Orbit 1 Flashcards

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1
Q

What are the dimensions of the orbit?

A

Volume: 30 cubic cmHeight: 35 mmWidth: 40mm

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2
Q

Where is the widest portion of the orbit?

A

Approximately 1 cm behind the anterior orbital rim

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3
Q

What are the 7 bones that comprise the orbital walls?

A

Maxilla, zygomatic, frontal, lacrimal, ethmoidal, palatine, sphenoid

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4
Q

How long is the optic canal?

A

8-10mm

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5
Q

What is the periorbita?

A

Periosteum covering the orbital bones

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6
Q

Arcus marginalis

A

The line of fusion at the anterior orbital rim of the periorbita, orbital septum, and periosteum of the facial bones

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7
Q

What are the lengths of the different segments of the optic nerve?

A

Intraocular: 1mmIntra orbital: 25mmIntracanalicular: 10Intracranial: 10

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8
Q

What is the only EOM that does not originate at the orbital apex?

A

IO

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9
Q

What is the best imaging modality for evaluating the orbital apex?

A

MRI

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10
Q

What muscles originate at the annulus of zinn?

A

The 4 rectus muscles

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11
Q

What is the only cn that innervates an EOM and does not pass through the intraconal space?

A

CN IV

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12
Q

What amount of asymmetry on hertels suggests proptosis

A

2mm

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13
Q

What is a “worms eye view”?

A

Evaluating globe position from below. In contrast to birds eye view from above

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14
Q

What are some common causes of pseudoptosis?

A

Enophthalmos, asymmetry of globe size, asymmetry of palpebral fissures such as in eyelid retraction

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15
Q

Exorbitism

A

An angle between the lateral orbital walls of greater than 90 degrees

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16
Q

Hypertelorism

A

Wider than normal (2.5cm) separation between the medial walls of the orbit

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17
Q

Telecanthus

A

A wide intercanthal distance

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18
Q

Hyperglobus and hypoglobus

A

Deviation up or down of the globe

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19
Q

Anophthalmia

A

Total absence of tissue of the eye

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20
Q

What are the three types of anophthalmia?

A
  1. Primary anophthalmia: when the primary optic vesicle fails to grow out from the cerebral vesicle at the 2mm stage2. Secondary anophthalmia: gross abnormality of the anterior neural tube3. Consecutive anophthalmia: secondary degeneration of the optic vesicle
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21
Q

Microphthalmia

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A

Presence of a small eye

22
Q

What is the most common location of a dermoid cyst?

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A

Adjacent to the frontozygomatic suture

23
Q

How should a dermoid cyst be managed?

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A

Complete excision with care not to rupture the cyst wall

24
Q

Where are dermolipomas usually located?

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A

Laterally on the globe and subjunctivally

25
How are dermolipomas usually treated
Observation, occasionally incomplete anterior resection
26
In the 20% of TED patients actually requiring surgery, what is the order of surgery type that should be performed?
Orbital decompression, strabismus, eyelid
27
On average, how long is the active phase of TED?
1 year or 2-3 years if a smoker
28
What is the most common clinical feature of TED?
Eyelid retraction
29
Does TED usually follow serum levels of t3 and t4?
No
30
What is the most common microorganism causing canaliculitis?
Actinomyces isrealiei
31
What is the distance from orbital rim to anterior ethmoid foramen? Anterior ethmoid foramen to posterior ethmoid foramen? Posterior ethmoid foramen to optic formen?
24, 12, 6
32
What is the only rectus muscle that only has one arterial supply?
Lateral rectus
33
What is a distinguishing difference of meningioma compared to fibrous dysplasia?
Meningioma have dural extensions best visualized on mr imaging.
34
What is the most common benign orbital tumor in adults?
Cavernous hemangioma
35
What is the most common malignant orbital tumor in adults?
Lymphoma
36
What is the most common benign orbital tumor in children
Capillary hemangioma
37
What is the most common malignant orbital tumor in children?
rhabdomyosarcoma
38
What is the most common primary intraocular tumor in adults?
Melanoma
39
What is the most common primary intraocular tumor in children?
retinoblastoma
40
What 2 bones comprise the roof of the orbit?
Frontal and lesser wing of the sphenoid
41
What 2 bones comprise the lateral orbital wall?
Zygomatic and greater wing of the sphenoid
42
What 4 bones comprise the medial orbital wall?
Ethmoid, lacrimal, sphenoid, and maxillary
43
What 3 bones comprise the floor of the orbit?
Maxillary, zygomatic, and palatine
44
What structures pass through the superior orbital fissure?
CN III, IV, VI, and V1; sympathetic fibers, and major venous drainage to cavernous sinus
45
Uncommonly subperiosteal abscesses can be observed instead of drained such as when the following are ABSENT: SPA is large, presence of frontal sinusitis, acute retinal/optic nerve damage, etc. What in regards to age and location are more convincing to observe?
If the age is LESS than 9 and if located in the usual medial location
46
What is the usual inciting organism causing necrotizing fasciitis?
Group A beta-hemolytic strep
47
Pretibial myxedeam and acropachy (soft=tissue swelling and periosteal changes affecting the distal extremities) portends a poorer or better prognosis in TED?
poorer
48
What structures pass through the inferior orbital fissue?
1. V2 (maxillary branch of CN V)2. inferior orbital vein3. branches of the sphenopalatine ganglion (not as important to memorize)
49
What is the most common EOM injured in cosmetic eyelid surgery?
IO
50
It is better to perform an optic nerve sheath fenetration at the time of active symptoms or not in a patient with pseudotumor cerebri?
At the time of active symptoms as the increased CSF pressure would cause engorgement and better visualization

Orbit (3 decks)

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