Lens Flashcards Preview

Ocular Physiology 2 > Lens > Flashcards

Flashcards in Lens Deck (100)
Loading flashcards...
1

What are the 3 things that need to happen properly for the lens to function

1. Be transparent
2. Have a higher index of refraction than the medium its suspended in (AH)
3. Have flexible refractive surfaces with the proper curvature

2

Disruption of the organization of the lens fiber cells or damage to the proteins result in

Cataract Formation

3

What type of cells does the anterior surface of the lens (lens epithelium) contain?

Cuboidal cells

4

What does the bulk of the lens consist of

Elongated fiber cells

5

What is secreted by the lens epithelium and elongated fiber cells

Lens capsule, an ECM

6

Where do most epithelial cells divide

In the germanative zone, near the equatorial margin of the lens epithelium

7

What are sutures

Junctions between the apical and basal ends of the cells from the opposite side of the lens

8

Lens increases in size and synthesis just before...

organelle degradation

9

Where do zonules originate

Non pigmented layer of the ciliary epithelium and insert into the lens capsule near the equator

10

What do tensions in the zonules cause

Curvature changes during accomodation

11

The refractive properties of the lens are the result of...

High concentrations of crystallins in the cytoplasm of the lens fiber cells and the curvature of the lens surfaces

12

Crystallins are how many times more higher than in typical cells

3x, which increases the refractive index of the lens
which makes up 40% of the wet weight of the lens fiber

13

In younger indivisuals, is refractive error caused by the lens?

NO

14

What are the 2 things that causes refractive error in younger indivisuals

1. Corneal curvature
2. Length of the globe

15

What does transparency of the lens depend upon?

Minimizing light scattering and absorption

16

Light passes smoothly through due to:

1. Regular structure of lens fibers
2. The absence of membrane bound organelles
2. Small/uniform extracellular space between cells

17

In young individuals the human lens is nearly...

Colorless

18

As we age, what wavelength of light does the lens absorb

Blue light which consists of short wavelengths

19

What is aphakia?

The absence or removal of the natural crystalline lens from natural causes

20

What is congenital aphakia

Rubella infection in first 4 weeks of pregnancy

21

What is pseudophakia

The substitution of the natural crystalline lens with a synthetic lens

22

What does lens fiber differentiation depend on

Synthesis and accumulation of large amounts of crystallins

23

What consist of the classical crystallins

Alpha crystallin family and Beta/gamma crystallin superfamily (all vertebrae lenses accumulate these)

24

What are taxon specific crystallins

Functional enzymes or proteins that are structurally similar to enzymes but that lack enzymatic activity

25

Do adult lenses produce taxon specific crystallins

NO

26

What enzyme is in the embryonic nucleus which serves as a taxon specific crystallin during the early development of the human lens

Betaine-homocysteine methyltransferase

27

What type of classical alpha crystallins do humans express

alpha A and alpha B

28

What is the role of alpha A and alpha B classical crystallins?

To prevent protein aggregation and precipitation

29

What did the analysis of the alpha A knockout in mice show

That the lens is smaller than normal but structurally similar, formation of cataracts in a few weeks, and that they contained large amounts of alpha B crystallin and smaller amounts of other proteins

30

Where else is the alpha B crystallin present besides the lens

Heart and skeletal muscle