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Orbit > Orbit 1 > Flashcards

Orbit 1 Flashcards

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

A

Presence of a small eye

22
Q

What is the most common location of a dermoid cyst?

A

Adjacent to the frontozygomatic suture

23
Q

How should a dermoid cyst be managed?

A

Complete excision with care not to rupture the cyst wall

24
Q

Where are dermolipomas usually located?

A

Laterally on the globe and subjunctivally

25
Q

How are dermolipomas usually treated

A

Observation, occasionally incomplete anterior resection

26
Q

In the 20% of TED patients actually requiring surgery, what is the order of surgery type that should be performed?

A

Orbital decompression, strabismus, eyelid

27
Q

On average, how long is the active phase of TED?

A

1 year or 2-3 years if a smoker

28
Q

What is the most common clinical feature of TED?

A

Eyelid retraction

29
Q

Does TED usually follow serum levels of t3 and t4?

A

No

30
Q

What is the most common microorganism causing canaliculitis?

A

Actinomyces isrealiei

31
Q

What is the distance from orbital rim to anterior ethmoid foramen? Anterior ethmoid foramen to posterior ethmoid foramen? Posterior ethmoid foramen to optic formen?

A

24, 12, 6

32
Q

What is the only rectus muscle that only has one arterial supply?

A

Lateral rectus

33
Q

What is a distinguishing difference of meningioma compared to fibrous dysplasia?

A

Meningioma have dural extensions best visualized on mr imaging.

34
Q

What is the most common benign orbital tumor in adults?

A

Cavernous hemangioma

35
Q

What is the most common malignant orbital tumor in adults?

A

Lymphoma

36
Q

What is the most common benign orbital tumor in children

A

Capillary hemangioma

37
Q

What is the most common malignant orbital tumor in children?

A

rhabdomyosarcoma

38
Q

What is the most common primary intraocular tumor in adults?

A

Melanoma

39
Q

What is the most common primary intraocular tumor in children?

A

retinoblastoma

40
Q

What 2 bones comprise the roof of the orbit?

A

Frontal and lesser wing of the sphenoid

41
Q

What 2 bones comprise the lateral orbital wall?

A

Zygomatic and greater wing of the sphenoid

42
Q

What 4 bones comprise the medial orbital wall?

A

Ethmoid, lacrimal, sphenoid, and maxillary

43
Q

What 3 bones comprise the floor of the orbit?

A

Maxillary, zygomatic, and palatine

44
Q

What structures pass through the superior orbital fissure?

A

CN III, IV, VI, and V1; sympathetic fibers, and major venous drainage to cavernous sinus

45
Q

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?

A

If the age is LESS than 9 and if located in the usual medial location

46
Q

What is the usual inciting organism causing necrotizing fasciitis?

A

Group A beta-hemolytic strep

47
Q

Pretibial myxedeam and acropachy (soft=tissue swelling and periosteal changes affecting the distal extremities) portends a poorer or better prognosis in TED?

A

poorer

48
Q

What structures pass through the inferior orbital fissue?

A
  1. V2 (maxillary branch of CN V)2. inferior orbital vein3. branches of the sphenopalatine ganglion (not as important to memorize)
49
Q

What is the most common EOM injured in cosmetic eyelid surgery?

A

IO

50
Q

It is better to perform an optic nerve sheath fenetration at the time of active symptoms or not in a patient with pseudotumor cerebri?

A

At the time of active symptoms as the increased CSF pressure would cause engorgement and better visualization

Orbit (3 decks)

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