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Ocular Block 7 > Crystalline Lens > Flashcards

Crystalline Lens Flashcards

1
Q

What is the space surrounding the lens called

A

Circumlental space

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2
Q

How much of the eyes optical power does the lens have

A

1/3

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3
Q

What is special about the lens

A

Pliable to change shape

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4
Q

Vasculature to the lens

A

Avascular

Depends on aqueous

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5
Q

Shape of lens

A

Biconvex
Plus on both sides
Converging to retina

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6
Q

Power of the lens

A

+15D

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7
Q

Which side of the lens has a smaller radius of curvature

A

Posteiror (its steeper)

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8
Q

Which side of the lens has a larger radius of curvature (flatter)

A

Anterior curvature

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9
Q

What is the axis of the lens

A

A line drawn from the anterior pole to the posterior pole

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10
Q

What is the equator of the lens

A

A line drawn from the top to the bottom of the lens

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11
Q

Lens diamter at birth

A

6.5mm

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12
Q

Diameter of adult lens

A

10mm diameter, 4mm thick unaccommidated

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13
Q

When does the lens stop increasing in size

A

After adolescence

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14
Q

Diameter vs thickness of the lens with age

A

The diameter of the adult lens does not increase significantly with age, however, thickness increases 0.02mm/year

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15
Q

What veggie is the lens like

A

Onion

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16
Q

Why is accommodation affected with age

A

As more layers are formed, central portion of lens gets compacted, less pliable

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17
Q

How much of the power of the eye does the lens account for

A

+15-20D of the total +60D of the eye

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18
Q

Range of dioptric power at age 40

A

Reduced to +8D

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19
Q

What is the dioptric power of the lens at age 60

A

+1 to 2D

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20
Q

Index of refraction of lens

A

Non uniform IR due to non uniform distribution of crystallin proteins in the lens fibers. Highest towards center and posteriorly

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21
Q

What do the zonules do for the lens

A

Keep the lens suspended, attached to pars plicata and into the capsule

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22
Q

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

A

0.5mm

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23
Q

Where does the vitreous attach to the lens

A

Wieger’s ligament

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24
Q

What is the indentation of the lens on the vitreous body called

A

Patellar fossa

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25
Q

What is the potential space between the lens and the vitreous body

A

Burgers space

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26
Q

What are the 3 parts of the lens

A
  1. Elastic capsule (BM, no elastic)
  2. Lens epithelium
  3. Elongated fibers
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27
Q

What is the largest BM of the human body

A

Elastic capsule of the lens (20 microns)

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28
Q

Which is thicker, anterior epithelium or lens fibers

A

Anterior epithelium

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29
Q

How does the lens epithelium become the lens fiber

A

Turns from elongated cuboidal cells to long fibers to lens fibers

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30
Q

Where is the posteiror epithelium of the lens

A

There isn’t any

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31
Q

What is the lens capsule in direct contact with

A

Anterior lens epithelium,

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32
Q

What is the capsule secreted by, anteriorly

A

By the anterior lens epithelium,

33
Q

What secretes the posteiror lens capsule?

A

Lens fibers, there is no epithelium posteriorly

34
Q

Which is thicker, anterior or posterior lens capsule

A

Anterior (20:3)

35
Q

What is the lens capsule composed of

A

Collagen

36
Q

What makes the lens capsule so elastic

A

Matrix of glycoproteins and sulfated proteoglycans allows lens to stretch up to 60%

37
Q

Where are the elastic fibers in the lens capsule

A

There are none, just elastic like properties

38
Q

What part of lens capsule increases with age

A

Anterior

39
Q

How much larger is the anterior lens capsule by age 65

A

1/3

40
Q

2 main functions of the lens capsule

A
  1. Diffusion barrier freely permeable low-molecular weight compounds (metabolites from aqueous)
  2. Makes the lens pliable to pull the zonular fibers during accommodation
41
Q

Outer most layer of the lens capsule to which the zonules will attach

A

Zonular lamella

42
Q

Monolayer of cuboidal cells

A

Lens epithelium

43
Q

Epithelial cell proliferation

A

Proliferate throughout life at the equator, cells stretch and become columnar shape

44
Q

Functions of lens epithelium

A
  1. Proliferates at germanative zones at equator to form lens fibers
  2. Central anterior epithelium is involved in the transport of substances from the aqueous humor to the lens interior
  3. Secretes the lens capsule
45
Q

What constitutes the bulk of the lens

A

Secondary lens fibers

46
Q

Originate from equator and take of the meridonal arrangement

A

Secondary lens fibers

47
Q

Basal portion of the secondary lens fibers

A

Creeps posteriorly along posteiror capsule

48
Q

As secondary lens fiber is pushed towards the center, the apical portion does what

A

Begins to elongate and situated itself under the anterior lens epithelium

49
Q

How do the nuclei of the secondary lens fibers sit

A

Nucleus moves anteriorly and sites more anterior than nuclei of newly formed fibers to form the lens bow and then finally disappears

50
Q

What is the lens bow

A

A curved line of nuclei of the secondary lens fibers, the more posterior the nucleus, the newer that fiber is

51
Q

How long is each lens fiber

A

10mm and U shaped

52
Q

Where do older fibers end up

A

Compacted on older fibers towards the center

53
Q

Ends of the fibers meet ends of fibers from other side of the lens at

A

Sutures

54
Q

As the lens increases in size, the lens fibers are unable to stretch that anteroposterior distance, so that progressively more complicated suture pattern are formed

A

Y sutures

55
Q

What does an anteiror Y suture look like

A

Upright Y

56
Q

What does a posterior Y suture look like

A

Inverted Y

57
Q

Cause of the Y sutures

A

Congenital

58
Q

Histology of lens fibers

A

Tongue/groove that fit together in the secondary fibers

59
Q

What kind of junctions are in the secondary lens fibers

A

Gap junctions for nutrients and ion exchange

60
Q

Once fibers have lost their nuclei, the organelles of the fiber become specialized to form _______ that make up the bulk of the fiber (40%)

A

Lens crystallins

61
Q

What is the thought to be the reason of the non uniform distribution of the refractive index of the lens

A

Non uniform destribution of the crystallins

62
Q

Earliest mass at center of lens composed of primary lens fibers. Formed at 2 months gestation. Does not increase in size

A

Embryonic nucleus

63
Q

Formed before birth, contains the Y sutures. Does not increase in size

A

Fetal nucleus

64
Q

Fibers made between birth and sexual maturation. Increases in size through life. They sclerose and become yellow with age

A

Adult nucleus

65
Q

Newly formed fibers that contain nuclei and surround adult nucleus

A

Lens cortex

66
Q

Divisions of the lens in order

A
  1. Anterior lens capsule
  2. Anteiror epithelium
    * cortex*
  3. Anterior surface of adult nucleus
  4. Anterior surface of fetal nucleus
  5. Anterior half embryonic nucleus
  6. Posteiror half embryonic nucleus
  7. Posterior surface fetal nucleus
  8. Posteiror surface adult nucleus
  9. Posterior line of disjunction
  10. posterior capsule
67
Q

What layer does the Y suture form on

A

Fetal nucleus

68
Q

Problems people have with cortical cataracts

A

When pupil is dilated, cortical cataracts cause a lot of glare because they are in the periphery. Near work/brighter conditions not as bad

69
Q

What happens to the lens in Marfan syndrome

A

The lens dislocates upwards

70
Q

In homocysteinuria, what happens to the lens

A

The lens dislocates downward

71
Q

Problems people have with posteiror subcapsular cataract

A

Problems reading, no problem seeing at night

72
Q

Cataract preop eval

A

-brightness acuity test

Make sure the VAs are worse than 20/50 before Sx

73
Q

How do they anesthetize the eye

A

Retrobulbar block, neelde behind globe

74
Q

Where do they normally make the incision for cataract Sx

A

Edge of cornea or on the limbus. Doing it on the limbus reduces chances of induced astigmatism

75
Q

What is the size of hte incision they make on cornea for cat sx today

A

3mm

76
Q

Steps of cat sx

A
  1. Anesthetize
  2. Corneal incision
  3. Anterior capsulorhexis (circular rip on anterior capsule)
  4. Hydrolineation (saline solution to detach cortex from capsule)
  5. Phacoemulsification (break down lens and sucks up the cataract)
  6. IOL insertion
  7. Stromal hydration
77
Q

Post op considerations

A
  • suture
  • patch or no patch
  • Abx and anti inflammatory therapy
  • 1 day FU, 3-14 days, 4-8 weeks
78
Q

This occurs when retained lens epithelial cells from the equator of the anterior capsule proliferate, undergo metaplasia, and then migrate across the posterior capsule

A

Posterior capsule opacification

79
Q

What is the most common complication of cataract surgery

A

Posterior capsule opacification (10-50%)

Ocular Block 7 (9 decks)

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