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Block 5; Week 2 > Orbit-Sievert > Flashcards

Orbit-Sievert Flashcards

1
Q

Describe the position of the medial & lateral walls of the orbit.

A

The medial walls are parallel to each other. The lateral walls are orthogonal to each other.

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2
Q

What forms the lens placode or vesicle?

A

this is formed b/c an out pocketing of the forebrain (diencephalon) induces thickening of the surface ectoderm. This forms the lens placode.

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3
Q

Why is it that the 1st & 2nd Cranial Nerves are not “true” cranial nerves?

A

this is b/c they both come from an out pocketing of the forebrain. You can’t follow a column all the way up to the forebrain.

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4
Q

Developmentally, where does the lens of the eye come from?

A

this comes from neural ectoderm

the lens breaks off of the lens placode

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5
Q

Developmentally, where does the cornea come from?

A

it comes from the remaining surface ectoderm–>once the lens broke off the lens placode.

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6
Q

Developmentally, where does the retina come from?

A

this comes from an out pocketing of brain tissue.

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7
Q

Where does the optic cup come from?

A

this comes from an out pocketing of forebrain

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8
Q

So, in total what does an out pocketing of forebrain tissue form?

A 
optic cup
retina
RPE
part of iris
part of ciliary bodies
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9
Q

What does RPE stand for? What is its function? What is it sandwiched b/w?

A

RPE: retinal pigmented epithelium
fcn: keeps light from bouncing around, helps with visual acuity
Sandwiched b/w: choroid below & retinal visual cells above.

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10
Q

Mesenchyme invades the orbit & gives rise to certain structures. What are they?

A

ciliary body
sclera
choroid

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11
Q

What’s the deal w/ sclera?

A

so this is equivalent to dura mater.
Actually, the dura mater has 2 layers. The periosteal layer goes along the bones of the orbit. The meningeal layer becomes the sclera after it follows along the optic nerve.

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12
Q

T/F The lens placode and optic cup together give rise to the cornea.

A

FALSE! The cornea comes from the surface ectoderm & underlying infiltrating mesenchyme.

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13
Q

T/F Cyclopia, anopthalmia & other severe eye defects are often associated with brain defects.

A

TRUE

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14
Q

What is Coloboma?

A

Think about the little girl at Sunday school.
This is a common defect where you see a key hole or cat’s eye.
Caused by incomplete closure of the choroid fissure.
Can sometimes have issues with letting too much light in.

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15
Q

What is the choroid fissure?

A
  • *this is a groove that develops for the invaginating hyaloid artery which runs from the posterior chamber to the lens
  • *the hyaloid artery later regresses & is only found as the central artery in the optic nerve
  • *it leaves the hyaloid canal
  • *if this fissure doesn’t close off properly you’ll get coloboma
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16
Q

What is the shape of the orbit? Where is its base & apex? How far apart are its medial walls?

A

It is pyramidal in shape.
Its base is near the front & is the orbital margin
the apex is @ the optic canal
the medial walls are 25 mm apart.

17
Q

If a muscle passes medial to the axis of the orbit, what is its action? What about if it passes lateral to the axis of the orbit?

A

Medial to Axis of Orbit: adducts

Lateral to Axis of Orbit: abducts

18
Q

What are the bones of the orbit? Which of these bones is particularly fragile?

A 
Frontal
Zygomatic
Maxillary
Lacrimal
Ethmoid**fragile b/c of air sinuses
Sphenoid
Palatine
19
Q

Superior & inferior to the orbit are important sinuses. What are they?

A

Superior: frontal sinus
Inferior: Maxillary sinus

20
Q

The infraorbital fissure is inferior to the orbit. It can be damaged in a blowout fracture. Which nerve could this damage? What is a random muscle that can be hurt by this injury?

A

V2.

Inferior Rectus Muscle

21
Q

Which part of the orbit collects your tears?

A

the lacrimal sac

22
Q

Which bone of the orbit has greater & lesser wings?

A

the sphenoid bone

23
Q

T/F There is an outer, middle, & inner layer of the orbit.

A

True.

24
Q

What is found in the outer layer of the orbit?

A

sclera (appears opaque)

cornea (translucent)

25
Q

What is found in your middle layer or pigmented layer?

A

choroid
ciliary body
iris

26
Q

What is found in your inner layer?

A

retina: visual & nonvisual parts

27
Q

Where roughly is the visual part of the retina?

A

more on the back of the eye, closer to the fovea
this includes the neural part of the retina & RPE
more rods & cones in this section

28
Q

Where roughly is the non visual part of the retina?

A

this is closer to the front of the eye, closer to the oro serrate

29
Q

Where do you find the most rods & cones in the eye? Why does this make sense?

A

Mostly near the fovea b/c you want good visual acuity (esp the cones). You also want some peripheral vision, so they will extend laterally. The cones decline more sharply than rods as you move out laterally.

30
Q

Where are the anterior & posterior chambers of the eye?

A

anterior is in front of the iris, beneath the cornea

the posterior is behind the iris but in front of the zonular fibers

31
Q

What are rods specialized for? Cones?

A

Rods–night vision, gross visual acuity

Cones–high visual acuity

32
Q

What is the natural shape of the lens? What do you have to do to change this shape? What type of vision is better with which shape?

A

Natural Shape: rounded up
Have to pull on the lens to flatten out…done w/ zonular ligaments.
Round Shape–>better for close up–>bend light more
Flat Shape–>better for far away–>lower refractive index

33
Q

Where is the vitreous body located? What it is composed of?

A

This is behind the lens & in the bulk of the eye
It is composed of 99% water, a colorless gel
found alongside the hyaloid canal

34
Q

Where are the ganglion cells found in the eye?

A

the ganglion cells of the retina are found lying in the layers of retina

35
Q

What are the factors that affect the refractive index of the eye?

A

lens shape
thickness of cornea (can’t change)
air water interface at the surface of the cornea

36
Q

Where is the optic disc located?

A

this is located where the optic nerve comes in with central retinal vessels
this is a blind spot

37
Q

What used to be in the hyaloid canal?

A

used to have the hyaloid artery, the central artery to the lens

38
Q

Which condition of the eye is associated w/ the optic disc?

A

papilledema
this is a condition where the subarachnoid space that surrounds the optic disc becomes inflamed with CSF b/c of increased intracranial pressure
**increased pressure could be from hydrocephalus, CVA, tumors.
**if untreated, could cause blurriness of vision or even blindness

39
Q

What is the macula? How does this relate to the fovea?

A

this is a pigmented spot near the back of the retina (not the same as the optic disc)
it contains the fovea where there is the highest conc’n of cone cells & visual acuity
makes up the optic axis?

Block 5; Week 2 (8 decks)

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