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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
How thick is the posterior lens capsule
3 microns
26
What collagen is the lens capsule made of
Type 4
27
What is the significance of the collagen fibers in the lens capsule
It allows the lens to stretch to 60% of its circumference without tearing
28
The anterior capsule increases with age
Yes
29
The anterior capsule is 1/3 larger by age 65
Yes
30
What are the 2 main functions of the lens capsule
1. diffusion barrier freely permeable low-molecular weight compounds 2. Makes the lens pliable to pull the zonular fibers during accommodation
31
What attaches at the outmost layer of the lens capsule
Zonules
32
What is the histology of the lens epithelium
Monolayer of cuboidal cells | There is no posterior epithelium
33
Why is there no posterior epithelium
It was used to make the primary lens fibers during development
34
Do the epithelial cells proliferate throughout life?
Yes
35
Where do the epithelial cells proliferate
Equator
36
The epithelial cells stretch to become columnar
Yes
37
What are the functions of the lens epithelium
- 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
What are the 2ndary lens fibers
They constitute the bulk of the lens
39
Where do the 2ndary lens fibers originate from
The equator
40
What arrangement do the 2ndary lens fibers have
Meridional
41
How do the nucleus move of the lens fibers
They move anteriorly and sit more anterior than the nuclei of newly formed fibers to form the lens bow then it disappears
42
How long are the lens fibers
10 mm
43
Where do the ends of fibers meet at
Sutures
44
As the lens increases in size , the lens fibers are unable to _______
Stretch
45
Posterior sutures are in the shape of a...
Upside down Y
46
Anterior sutures are in the shape of a
Erect Y
47
What occurs at the epithelium-fiber interface
Nutrient and ion exchange by gap junctions
48
Once fibers have lost their nuclei, the organelles become these
Crystallins
49
Crystallins make up what percentage of the fiber
40%
50
What is the embryonic nucleus
The earliest mass at the center of the lens
51
What is the embryonic nucleus composed of
Primary lens fibers
52
When does the embryonic nucleus form
2 weeks gestation
53
Does the embryonic nucleus increase in size?
No
54
When is the fetal nucleus formed
Before birth
55
What is located in the fetal nucleus
The Y sutures
56
Does the fetal nucleus increase in size
No
57
When is the adult nucleus formed
Between birth and sexual maturation
58
Does the adult nucleus increase in size?
Yes
59
What happens to the adult nucleus as we age
It sclerosis and yellows
60
What is the lens cortex
Newly formed fibers that contain nuclei that surround the adult nucleus
61
What are the divisions of the lens
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
What is a cortical cataract
A cataract that forms in the cortex of the lens. It has long fibers that extend that have become opacified
63
What happens to the lens in Marian's
The lens dislocates upward
64
What happens to the lens in homocysteinuria
The lens dislocations downward
65
What is the general order of a cataract surgery
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
What s posterior capsule opacification
When retained cells from the equator of the anterior capsule proliferate, undergo metaplasia, and migrate across the posterior surface
67
What is the most common complication of cataract surgery
Posterior capsule opacification
68
What is the occurrence of posterior capsule opacification
10-50%
69
What is the treatment done to correct posterior lens opacification
No:YAG or YAG

Ocular Block 7 (9 decks)

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