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Ocular Block 7 > Crystalline Lens > Flashcards

Crystalline Lens Flashcards

1
Q

What is the crystalline lens

A

A biconvex structure

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2
Q

What is the lens posterior to

A

Iris and pupil

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3
Q

What is the lens anterior to

A

The vitreous body

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4
Q

What surface of the lens is steeper

A

The posterior (5-8 mm ROC)

The anterior is 8-14 mm RoC

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5
Q

Where are the poles of the lens

A

In the center of the anterior and posterior curvatures

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6
Q

What is the axis of the lens

A

The line connecting the 2 poles

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7
Q

What is the diameter of the lens at birth

A

6.5 mm

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8
Q

What is the diameter and thickness of the lens in an adult

A

10 mm diameter

4 mm thick

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9
Q

T/F the diameter of the lens changes significantly as we age

A

False, it does not increase significantly

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10
Q

The thickness of the lens increases by this amount every year

A

0.02 mm/yr

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11
Q

The total power of the eye is approximately

A

+60D

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12
Q

The lens accounts for _____ D of the total power of the eye

A

15-20D

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13
Q

The range of power of the lens is reduced by this amount by age 40

A

+8D

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14
Q

At age 60 what is the range of power of the lens

A

+1-2D

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15
Q

What causes the non uniform refractive index of the lens

A

The non-uniform distribution of crystallin proteins

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16
Q

What is the purpose of the anterior lens zonules

A

They keep the lens in position

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17
Q

The lens equator is _______ away from the ciliary processes of the pars plicata

A

0.5 mm

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18
Q

What attaches the posterior surface of the lens to the vitreous

A

Weiger’s ligament (there are 2)

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19
Q

What is the space where the lens sits

A

The patellar fossa

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20
Q

What are the 3 parts of the crystalline lens

A

Elastic capsule
Lens epithelium
Lens fibers

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21
Q

What is the thickness of the anterior lens capsule

A

20 microns (thickest in the body)

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22
Q

The lens capsule is in direct contact with this

A

The anterior lens epithelium

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23
Q

What secretes the anterior lens capsule

A

Anterior lens epithelium

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24
Q

Why is the posterior capsule so thin?

A

Because there is no posterior lens epithelium

The posterior capsule is secreted by lens fibers

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25
Q

How thick is the posterior lens capsule

A

3 microns

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26
Q

What collagen is the lens capsule made of

A

Type 4

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27
Q

What is the significance of the collagen fibers in the lens capsule

A

It allows the lens to stretch to 60% of its circumference without tearing

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28
Q

The anterior capsule increases with age

A

Yes

29
Q

The anterior capsule is 1/3 larger by age 65

A

Yes

30
Q

What are the 2 main functions of the lens capsule

A
  1. diffusion barrier freely permeable low-molecular weight compounds
  2. Makes the lens pliable to pull the zonular fibers during accommodation
31
Q

What attaches at the outmost layer of the lens capsule

A

Zonules

32
Q

What is the histology of the lens epithelium

A

Monolayer of cuboidal cells

There is no posterior epithelium

33
Q

Why is there no posterior epithelium

A

It was used to make the primary lens fibers during development

34
Q

Do the epithelial cells proliferate throughout life?

A

Yes

35
Q

Where do the epithelial cells proliferate

A

Equator

36
Q

The epithelial cells stretch to become columnar

A

Yes

37
Q

What are the functions of the lens epithelium

A
  • Proliferate at germanative zone at equator to from lens fibers
  • anterior central: transport of substances from aqueous to interior lens
  • secretes lens capsule (anterior)
38
Q

What are the 2ndary lens fibers

A

They constitute the bulk of the lens

39
Q

Where do the 2ndary lens fibers originate from

A

The equator

40
Q

What arrangement do the 2ndary lens fibers have

A

Meridional

41
Q

How do the nucleus move of the lens fibers

A

They move anteriorly and sit more anterior than the nuclei of newly formed fibers to form the lens bow then it disappears

42
Q

How long are the lens fibers

A

10 mm

43
Q

Where do the ends of fibers meet at

A

Sutures

44
Q

As the lens increases in size , the lens fibers are unable to _______

A

Stretch

45
Q

Posterior sutures are in the shape of a…

A

Upside down Y

46
Q

Anterior sutures are in the shape of a

A

Erect Y

47
Q

What occurs at the epithelium-fiber interface

A

Nutrient and ion exchange by gap junctions

48
Q

Once fibers have lost their nuclei, the organelles become these

A

Crystallins

49
Q

Crystallins make up what percentage of the fiber

A

40%

50
Q

What is the embryonic nucleus

A

The earliest mass at the center of the lens

51
Q

What is the embryonic nucleus composed of

A

Primary lens fibers

52
Q

When does the embryonic nucleus form

A

2 weeks gestation

53
Q

Does the embryonic nucleus increase in size?

A

No

54
Q

When is the fetal nucleus formed

A

Before birth

55
Q

What is located in the fetal nucleus

A

The Y sutures

56
Q

Does the fetal nucleus increase in size

A

No

57
Q

When is the adult nucleus formed

A

Between birth and sexual maturation

58
Q

Does the adult nucleus increase in size?

A

Yes

59
Q

What happens to the adult nucleus as we age

A

It sclerosis and yellows

60
Q

What is the lens cortex

A

Newly formed fibers that contain nuclei that surround the adult nucleus

61
Q

What are the divisions of the lens

A
  1. Anterior capsule
  2. Anterior epithelium
  3. Anterior surface of adult nucleus
  4. Anterior surface of fetal nucleus
  5. Anterior half of embryonic nucleus
  6. Posterior half of embryonic nucleus
  7. Posterior surface of fetal nucleus
  8. Posterior surface of adult nucleus
  9. Posterior line of disjunction
  10. Posterior capsule
62
Q

What is a cortical cataract

A

A cataract that forms in the cortex of the lens. It has long fibers that extend that have become opacified

63
Q

What happens to the lens in Marian’s

A

The lens dislocates upward

64
Q

What happens to the lens in homocysteinuria

A

The lens dislocations downward

65
Q

What is the general order of a cataract surgery

A
  1. Pre-op brightness acuity test
  2. Anesthesia, retrobulbar block
  3. Corneal incision (near limbus or on cornea)
  4. Anterior capsulorhexis
  5. Hydrodelineation
  6. Phacoemulsification
  7. IOL insertion
  8. Stromatolites hydration
  9. Post op
66
Q

What s posterior capsule opacification

A

When retained cells from the equator of the anterior capsule proliferate, undergo metaplasia, and migrate across the posterior surface

67
Q

What is the most common complication of cataract surgery

A

Posterior capsule opacification

68
Q

What is the occurrence of posterior capsule opacification

A

10-50%

69
Q

What is the treatment done to correct posterior lens opacification

A

No:YAG or YAG

Ocular Block 7 (9 decks)

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