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B7 Ocular > Crystalline Lens > Flashcards

Crystalline Lens Flashcards

1
Q

Which side of the lens is flatter? Steeper?

A

Anterior side is flatter and posterior side is steeper.

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2
Q

Lens diameter at birth

A

6.5 mm

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3
Q

Lens diameter in an adult

Thickness?

A

10 mm

4 mm thick

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4
Q

Does the lens diameter increase with age?

A

No. But the thickness does. About 0.02 mm/yr

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5
Q

What is the most peripheral edge of the lens called? What happens here?

A

The equator of the lens, the marginal circumference of the lens.

This is where cell proliferation occurs

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6
Q

The Lens accounts for ___D of the total __D of the eye.

A

+15-20 D

+60 D

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7
Q

By age 40, what is the range of dioptric power reduced to? Why?

A

+8 D, hence onset of presbyopia

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8
Q

By age 60, what is the range of dioptric power reduced to?

A

+1 to 2 D

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9
Q

Why is there a non-uniform index of refraction in the lens?

A

Due to the non-uniform distribution of crystallin proteins in the lens fibers

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10
Q

Suspensory apparatus that holds the lens in place and attaches to the capsule of the lens

A

Lens zonules

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11
Q

How far is the lens equator from the ciliary processes of the pars plicata?

A

0.5 mm

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12
Q

Structure that attaches posterior surface of the lens to the vitreous body

A

Wieger’s ligament

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13
Q

Space between lens and vitreous

A

Berger’s space

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14
Q

The depression of the vitreous where the lens sits

A

Patellar fossa

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15
Q

3 parts of the crystalline lens

A
  1. Elastic capsule
  2. Lens epithelium
  3. Lens fibers
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16
Q

What acts as the basement membrane of the lens?

A

Elastic capsule

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17
Q

The elastic capsule is secreted by…

A

The anterior epithelium

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18
Q

There is no ____________ epithelium in the mature lens

A

Posterior

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19
Q

Where is the lens capsule the thickest?

A

Anteriorly, 20 microns

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20
Q

The lens capsule is in direct contact with :

A

The anterior lens epithelium

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21
Q

How thick is the posterior lens capsule?

A

3 microns thick.

There is no epithelium posteriorly, so the lens fibers secrete the posterior lens capsule

22
Q

What allow the lens to stretch?

A

The collagen embedded within the glycoproteins and sulfate proteoglycans
–allows it to stretch up to 60% of its circumference without tearing

NO elastic fibers in the capsule.

23
Q

What part of the capsule increases with age?

A

Anterior capsule, by 65 yrs old it will be 1/3 larger!

24
Q

2 main functions of the lens capsule

A
  1. Diffusion barrier freely permeable low-molecular weight compounds
  2. Makes the lens pliable for zonular fibers in accommodation
25
Q

Outermost layer of the lens capsule to which where to zonules will attach

A

Zonular lamella

26
Q

What type of cells are the lens epithelium anteriorly? Equatorially? Posteriorly?

A

Anteriorly = monolayer of cuboidal cells

Equatorially = germanative zone, where proliferation occurs, cells stretch and become columnar shape

Posteriorly = there isn’t a posterior epithelium silly

27
Q

What is the function of the lens epithelium at the equator? Everywhere else?

A

Proliferation, “germinative zone” to create lens fibers.

ALL of the lens epithelium secretes the lens capsule and transport of substances from aqueous humor to lens anterior.

28
Q

Which type of fibers constitute the bulk of the lens?

A

Secondary lens fibers

29
Q

Where do secondary lens fibers originate?

A

The equator, it will elongate as it is pushed towards the center. The nucleus will move anteriorly over time, and will eventually disappear. MAGIC

30
Q

What happens to the lens fibers that lose their nuclei?

A

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

31
Q

The ends of the lens fibers meet ends of lens fibers from the other side of the lens

A

Sutures

32
Q

Why are Y sutures created?

A

The lens keeps increasing in size, and its lens fibers are unable to stretch the anteroposterior distance, so they compact into Y formations

Can cause problems, like sutural cataracts.

33
Q

How do secondary lens fibers communicate with each other?

A

Gap junctions

Nutrient and ion exchange occurs here

34
Q

Once fibers have lost their nuclei, the organelles of the fiber become specialized to form:

How much of the fiber do these make up?

A

Lens crystallins

40%

35
Q

The non-uniform distribution if crystallins is thought to give the lens a _______________ ______________ ________.

A

Non-uniform refractive index

36
Q

What are the 4 layers/divisions of the lens?

Not including the capsule.

A
  1. Embryonic nucleus
  2. Fetal nucleus
  3. Adult nucleus
  4. Lens cortex
37
Q

Which layer of the lens is composed of primary lens fibers?

A

Embryonic nucleus

38
Q

Which layer of the lens contains the Y-sutures?

A

Fetal nucleus

39
Q

Which layer of the lens contains secondary fibers and increases with size?

A

Adult nucleus

40
Q

Which layer of the lens becomes yellow with age?

A

Adult nucleus

41
Q

Which layer of the lens contains newly formed fibers that contain nuclei? (And surrounds adult nucleus)

A

Lens cortex

42
Q

If you have trouble driving at night, without any issues with reading, what type of cataract would you have?

A

Cortical cataract

Because large pupils will reveal the issues of a cataract in the cortex

43
Q

What is ectopia lentis? When is it most common? (2 diseases)

A

Dislocation of the lens.

Common in Marfan’s syndrome, will dislocate UPWARD.

In homocysteinuria, lens will dislocate DOWNWARD.

44
Q

If you have trouble reading, but not driving at night, what type of cataract will you have?

A

Posterior subcapsular cataract.

Small and in the middle, so small pupil reveal it.

45
Q

Test where you check VAs and if they’re a candidate for cataract surgery

A

Brightness acuity test/cataract preoperative evaluation

46
Q

What is retrobulbar block?

A

Where you inject an anesthetic transconjunctivally to numb the long cilary nerves

47
Q

Saline solution that disconnects cortex from capsule

A

Hydrolineation

48
Q

Process of breaking down the lens and auctioning pieces out

A

Phacoemulsification

49
Q

What is the most common complication of cataract surgery?

A

Complete removal of ALL lens epithelial cells. Posterior lens capsule and a portion of the anterior capsule remain in place to support a posterior chamber lens. This will cause posterior capsular opacification.

10%-50% of patients.

50
Q

What is pseudophakia?

A

Placement of IOL where lens was

B7 Ocular (6 decks)

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