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Block 7 - Ocular Anatomy > Crystalline Lens > Flashcards

Crystalline Lens Flashcards

1
Q

In which chamber is the lens located?

A

Posterior chamber

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2
Q

Does the lens have a blood supply?

A

No - avascular

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3
Q

How does the lens get its nutrients?

A

Aqueous humor (lens is avascular)

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4
Q

What is considered the major refractive component of the eye?

A

Cornea

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5
Q

About how strong (diopters) is the lens?

A

15-20 D

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6
Q

Describe the structure (type) of the crystalline lens.

A

Biconvex - Plus on both sides

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7
Q

Describe the location of the crystalline lens

A

Within the posterior chamber.
Posterior to the iris and pupil.
Anterior to vitreous body.

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8
Q

Which pole of the lens is steeper? What does this curvature imply?

A

Posterior pole is steeper - smaller radius of curvature

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9
Q

Which pole of the lens is flatter?

A

Anterior pole

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10
Q

Where is the axis of the lens?

A

Connects the anterior pole and posterior pole (horizontal)

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11
Q

Where is the equator of the lens?

A

Connects the most superior point of lens with most inferior point (vertical)

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12
Q

What is the diameter (height) of the lens at birth?

A

6.5 mm

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13
Q

What is the diameter (height) of the lens after adolescence?

A

10 mm

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14
Q

What represents the diameter of the lens: axis or equator?

A

Equator

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15
Q

How does the adult lens change with age?

A

Thickness increases 0.02 mm/year.

The diameter does not increase significantly.

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16
Q

Is the thickness or diameter larger in the crystalline lens?

A

Diameter

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17
Q

What characteristic of the aging lens contributes to cataract formation?

A

Cells continuously dividing and reproducing with no change in diameter results in the cells getting very compacted/crowded.
The crowded cells are responsible for the yellowing/opacity of the lens - cataract.

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18
Q

What is the (unaccommodated) thickness of the adult lens?

A

4 mm

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19
Q

What is the power of a 40 year old’s lens?

A

8 D

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20
Q

What is the power of a 60 year old’s lens?

A

1-2 D

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21
Q

What is the reason for the non-uniform index of refraction in the crystalline lens?

A

Non-uniform distribution of crystallin proteins in the lens fibers

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22
Q

Where is the index of refraction higher?

A

Towards center and posterior

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23
Q

Which two structures does the Wieger’s Ligament attach?

A

Posterior surface of lens and vitreous

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24
Q

What is the patellar fossa?

A

The indent formed by the lens resting on Wieger’s Ligament

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25
Q

Where is Berger’s Space?

???

A

???Between the patellar fossa and Wieger’s Ligament???

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26
Q

If you were to remove the cornea and sclera, and then pull the lens out, what would go with it? Why?

A

Vitreous - because it is connected to the lens via Wieger’s Ligament

27
Q

What are the three parts of the crystalline lens?

A
  1. Elastic capsule
  2. Lens epithelium
  3. Lens fibers
28
Q

How thick is the anterior elastic capsule?

A

20 microns

29
Q

What part of the crystalline lens is the thickest in the entire body?

A

Elastic capsule (anterior)

30
Q

How does the anterior and posterior capsules differ?

A

Anterior has epithelium, posterior does not

31
Q

What is the function of the anterior lens epithelium?

A

Secretes anterior lens capsule

32
Q

Where is the posterior lens capsule secreted from?

A

Lens fibers

33
Q

How thick is the posterior lens capsule?

A

3 microns

34
Q

What are the 2 main functions of the lens capsule?

A
  1. Diffusion barrier freely permeable to low-molecular weight compounds (metabolites from aqueous humor)
  2. Makes the lens pliable to the pull of zonular fibers during accommodation.
35
Q

Are there elastic fibers in the capsule?

A

No

36
Q

What is the lens capsule composed of?

A

Collagen Type IV within a matrix of glycoproteins and sulfated proteoglycans

37
Q

Why is the composition of the lens capsule significant?

A

Allows the lens to stretch up to 60% of its circumference without tearing

38
Q

Does the anterior lens increase or decrease with age? By how much?

A

Increases by 1/3 by the age of 65

39
Q

What is the zonular lamella?

A

Outermost layer of the lens capsule where the zones attach

40
Q

What type of cells is the lens epithelium composed of?

A

Monolayer of cuboidal cells

41
Q

During development, what were the posterior epithelium cells used for?

A

Primary lens fibers

42
Q

Do epithelial cells proliferate throughout life?

A

Yes

43
Q

Where do epithelial cells proliferate throughout life?

A

At the equator - the germinative zone

44
Q

What shape are the epithelial cells at the germinative zone?

A

Stretched cuboidal = columnar shape

45
Q

What are the 3 functions of the lens epithelium?

A
  1. Proliferates at germinative zone to form lens fibers
  2. Central anterior epithelium is involved in the transport of substances from aqueous humor to lens interior
  3. Secretes the lens capsule
46
Q

What makes up the bulk of the lens?

A

Secondary lens fibers

47
Q

Where do the secondary lens fibers originate from?

A

Equator

48
Q

What happens to the apical portion of the lens fibers as they are pushed toward the center?

A

Apical portion begins to elongate and situates itself under the anterior lens epithelium

49
Q

What happens to the nucleus of the lens as the fibers are pushed toward the center?

A

Nucleus moves anteriorly and sits more anteriorly than the nuclei of the newly formed fibers. This forms the lens bow and then finally disappears

50
Q

What happens when lens fibers lose nuclei?

A

The fibers detach from capsule and are compacted on older fibers towards the center

51
Q

Where do the ends of fibers from one side meet the ends from the other?

A

Sutures

52
Q

How long is each secondary lens fiber?

A

10 mm

53
Q

Why/When is there a Y-shaped suture formed?

A

When the lens increases in size, the fibers are unable to stretch from anterior to posterior

54
Q

How are nutrients and ions exchanged between the epithelium and fibers?

A

Gap junctions

55
Q

What makes up the bulk of lens fibers?

A

Alpha and Beta lens crystalline (protein)

56
Q

How are lens crystallins formed?

A

When fibers lose their nuclei, the organelles of the fibers become specialized and form lens crystallins

57
Q 
Describe the divisions of the lens:
Embryonic Nucleus
Fetal Nucleus
Adult Nucleus
Lens Cortex
A

Embryonic Nucleus: Formed at 2 months gestation; does not increase in size; earliest mass at center of lens; composed of primary lens fibers
Fetal Nucleus: Formed before birth; contains Y sutures; does not increase in size
Adult Nucleus: Fibers made between birth and sexual maturation; increase in size throughout life; these slcerose and become yellow with age
Lens Cortex: Newly formed fibers that contain nuclei and surround adult nucleus

58
Q

Explain the dislocation of the lens in Marfan’s Syndrome and Homocysteinuria

A

Marfan’s: Dislocates upward

Homocysteinuria: Dislocates downward

59
Q

What is dislocation of the lens called?

A

Ectopic Lentis

60
Q

Explain the steps in cataract removal (7)

A
  1. Anesthesia: Retrobulbar Block - knocking out long ciliary nerve fibers
  2. Corneal Incision - can be in cornea or toward limbus
  3. Anterior Capsulorhexis
  4. Hydrodelineation - inject saline solution and cortex detaches from surrounding capsule
  5. Phacoemulsification - high frequency ultrasound breaks down cataract and chops it up. Then vibrations suck it up
  6. IOL Insertion - IOL is folded, inserted, unfolded and situated in center
  7. Stromal Hydration
61
Q

List post-op considerations

A
  • Suture
  • Patch or no patch
  • Topical antibiotics
  • Anti-inflammatory therapy
  • 1 day follow up, 3-14 day follow up, 4-8 week follow up
62
Q

What causes posterior capsule opacification?

A

Incomplete removal of all lens epithelial cells during cataract surgery - remaining anterior epithelial cells proliferate, undergo metaplasia, and then migrate across the posterior capsule

63
Q

What is the most common complication of cataract surgery? How common?

A

Posterior Capsule Opacification

10-50% of surgical cataract patients

64
Q

How is Posterior Capsule Opacification treated?

A

Nd:YAG laser

Block 7 - Ocular Anatomy (3 decks)

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