5 - Crystalline Lens

Question 1

Which region is the lens located in the eye?

Answer 1

Posterior Chamber

Question 2

What is the eye suspended by?

Answer 2

Zonular Fibers of the Ciliary Body

Question 3

What is the posterior part of the lens attached to?

Answer 3

Anterior Vitreous face by the Hyaloid Capsular Ligament

Question 4

What is the basic shape of the lens?

Answer 4

Convex

Note: The posterior part of the lens more steeper than the anterior

Question 5

What are the centers of the lens called?

Answer 5

Poles

Question 6

What is the normal thickness of the unaccommodated lens?

Answer 6

3.5 to 5 mm

Note: It increases 0.02 mm each year in life

Question 7

What is the refractive power of the unaccomodative eye?

Answer 7

20D

Question 8

True or False. The index of refraction increases as you go from anterior to posterior.

Answer 8

True

Note: The index of refraction changes due to increase amount of protein found in the lens

Question 9

What is the embryological composition of lens made of?

Answer 9

Epithelial cells

Question 10

What structure of the lens, during embryology, form the primary lens fibers?

Answer 10

Posterior cells

Note: This is why there is no posterior epithelium

Question 11

Where does cell division occur throughout life?

Answer 11

Germinative zone

Question 12

What part of the lens capsule becomes the thickest over time?

Answer 12

Anterior pole

Note: Posterior lens capsule changes very little over a period of age

Question 13

What is the lens capsule primarily made of?

Answer 13

Collagen fibers

Note: There are no elastic fibers but is highly elastic due to lamellar arrangement of the fibers

Question 14

What is the name of the superficial zone of the lens capsule, where zonular fibers are attached to?

Answer 14

Zonular Lamella

Question 15

What structure prevents large molecules to pass through the anterior of the lens?

Answer 15

Lens capsule

Question 16

Lens Epithelium

Answer 16

Page 94

Question 17

Since 80 to 90% of lens proteins are water soluble (alpha, beta, and gamma crystallins) which are packed in the CYTOPLASM of lens fiber cells, what can threaten the optical transparency of the lens?

Answer 17

UV Radiation

Question 18

What type of crystalline protein is considered the molecular chaperone?

Answer 18

Alpha crystalline

Note: Offers resistance to the degradation of gamma and beta crystalline

Question 19

True or False. The lens is more basic in pH compared to the Aqueous humor?

Answer 19

False.

Lens pH = 6.9
AH = 7.6
Plasma = 7.4

Question 20

Since, the crystallin concentration varies among the lens, where is the refractive index gradient highest?

Answer 20

Nucleus = 1.41
Outer Cortical Surface = 1.38

Note: The VH n=1.336

Question 21

As you know the lens is avascular and has the largest percent of protein in the body. Where does it get its nutrients from and what type of proteins does it require?

Answer 21

From the Aqueous and receives glucose and oxygen and maintains 2 functions:

1)Production of NEW LENS FIBERS and PROTEIN SYNTHESIS

2) Maintenance of Na/K pump.
- The lens is constantly pumping out water to create the correct constituents optically. Note: ATP is required to maintain a dehydrated lens

Question 22

True or False. Since there is ANAEROBIC GLYCOLYSIS, occuring in the lens epithlium, it has a higher concentration of lactic acid than blood plasma?

Answer 22

True.