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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
Where is Berger's Space? | ???
???Between the patellar fossa and Wieger's Ligament???
26
If you were to remove the cornea and sclera, and then pull the lens out, what would go with it? Why?
Vitreous - because it is connected to the lens via Wieger's Ligament
27
What are the three parts of the crystalline lens?
1. Elastic capsule 2. Lens epithelium 3. Lens fibers
28
How thick is the anterior elastic capsule?
20 microns
29
What part of the crystalline lens is the thickest in the entire body?
Elastic capsule (anterior)
30
How does the anterior and posterior capsules differ?
Anterior has epithelium, posterior does not
31
What is the function of the anterior lens epithelium?
Secretes anterior lens capsule
32
Where is the posterior lens capsule secreted from?
Lens fibers
33
How thick is the posterior lens capsule?
3 microns
34
What are the 2 main functions of the lens capsule?
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
Are there elastic fibers in the capsule?
No
36
What is the lens capsule composed of?
Collagen Type IV within a matrix of glycoproteins and sulfated proteoglycans
37
Why is the composition of the lens capsule significant?
Allows the lens to stretch up to 60% of its circumference without tearing
38
Does the anterior lens increase or decrease with age? By how much?
Increases by 1/3 by the age of 65
39
What is the zonular lamella?
Outermost layer of the lens capsule where the zones attach
40
What type of cells is the lens epithelium composed of?
Monolayer of cuboidal cells
41
During development, what were the posterior epithelium cells used for?
Primary lens fibers
42
Do epithelial cells proliferate throughout life?
Yes
43
Where do epithelial cells proliferate throughout life?
At the equator - the germinative zone
44
What shape are the epithelial cells at the germinative zone?
Stretched cuboidal = columnar shape
45
What are the 3 functions of the lens epithelium?
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
What makes up the bulk of the lens?
Secondary lens fibers
47
Where do the secondary lens fibers originate from?
Equator
48
What happens to the apical portion of the lens fibers as they are pushed toward the center?
Apical portion begins to elongate and situates itself under the anterior lens epithelium
49
What happens to the nucleus of the lens as the fibers are pushed toward the center?
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
What happens when lens fibers lose nuclei?
The fibers detach from capsule and are compacted on older fibers towards the center
51
Where do the ends of fibers from one side meet the ends from the other?
Sutures
52
How long is each secondary lens fiber?
10 mm
53
Why/When is there a Y-shaped suture formed?
When the lens increases in size, the fibers are unable to stretch from anterior to posterior
54
How are nutrients and ions exchanged between the epithelium and fibers?
Gap junctions
55
What makes up the bulk of lens fibers?
Alpha and Beta lens crystalline (protein)
56
How are lens crystallins formed?
When fibers lose their nuclei, the organelles of the fibers become specialized and form lens crystallins
57
``` Describe the divisions of the lens: Embryonic Nucleus Fetal Nucleus Adult Nucleus Lens Cortex ```
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
Explain the dislocation of the lens in Marfan's Syndrome and Homocysteinuria
Marfan's: Dislocates upward | Homocysteinuria: Dislocates downward
59
What is dislocation of the lens called?
Ectopic Lentis
60
Explain the steps in cataract removal (7)
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
List post-op considerations
- 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
What causes posterior capsule opacification?
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
What is the most common complication of cataract surgery? How common?
Posterior Capsule Opacification | 10-50% of surgical cataract patients
64
How is Posterior Capsule Opacification treated?
Nd:YAG laser

Block 7 - Ocular Anatomy (3 decks)

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