Lens

Question 1

Because the refractive power of the lens is variable, it permits

Answer 1

Focus on objects that’s are near or far

Question 2

Lens vascularization and innervation

Answer 2

Lens is avascular and no innervation

Question 3

What is vossius ring?

Answer 3

Blunt trauma causes iris to stick to the eye and you will see pigment cells on the anterior lens

Question 4

The lens is a ______ structure without any nerves or blood vessels

Answer 4

Purely epithelial structure

Question 5

The oldest cells of the lens are located

Answer 5

In the center of the lens

Youngest are always on the surface

Question 6

Small cuts and tears in the lens capsule will result in

Answer 6

Lens opacities

Question 7

The lens capsule is more fragile in

Answer 7

Diabetics

Having too much sugar makes the capsule weaker

Question 8

Lens capsule is secreted by

Answer 8

The basal cell area of the lens epithelium

Question 9

Lens is like an onion because ___ which affects ____.

Answer 9

New layers are added over a pts life span

Which produces an age related increase in thickness (harder to accommodate)

Question 10

Active layer of the lens is

Answer 10

Lens epithelium: a single layer of cuboidal cells which lies deep to the anterior capsule

Question 11

The bulk of the lens is composed of

Answer 11

Lens fiber

Question 12

Mitotic cells ___ with age

Answer 12

Decrease

Question 13

What layer is the most susceptible to radiation damage ?

Answer 13

Epithelial cells

Question 14

Mature lens fibers are cells which

Answer 14

Have lost their nuclei

Eliminates light scatter

Question 15

Extensive system of gap junctions that allow the lens to behave as one large cell

Answer 15

Syncytium

Question 16

The reason the cells lose their nuclei is to allow light to pass through

Answer 16

The lens nuclei would create light scatter and distort retinal images

Question 17

Epithelial transitions to

Answer 17

Fiber cell

Lens fibers are highly specialized terminally differentiated cells (cant do anything else)

Question 18

Lens sutures

Answer 18

Where lens fibers terminates upon each other (where they meet)
Can have a y suture cataract

Question 19

Zonules are primary made of

Answer 19

Fibrillin, a connective tissue protein

Contain cysteine

Question 20

In Marfans syndrome

Answer 20

Mutation in the fibrillin gene, will cause lens to be dislocated

Question 21

What is ectopic lentis

Answer 21

Lens dislocation/ subluxation

Zonular fibers are broken and the lens is no longer held securely in place but remains in pupil aperture

Question 22

Hydration of the lens

Answer 22

Relatively dehydrated organ

Low water is a neutral consequence of need for maintaining refractive index

Question 23

The majority of the lens protein is

Answer 23

Structural protein/ crystallin

Water soluble

Question 24

Most insoluble proteins are found in

Answer 24

The lens nucleus / oldest part of the eye

Question 25

Solubility decreases with age

Answer 25

Why we see cataracts on older people

Question 26

Water soluble structural proteins

Answer 26

Crystallins

Question 27

Crystallins are chaperones

Answer 27

Provides lens with oxidative stress resistant properties (chaperone like activity) They also prevent aggregation

Question 28

When crystallin become insoluble

Answer 28

Light scatter occurs

Question 29

Oxidation releases

Answer 29

Free radicals that tear up membranes

Question 30

Glutathione (GSH synthesis)

Answer 30

Important in lens, tries to minimize damage form oxidation

Question 31

A way to keep lens transparent is by

Answer 31

Maintainance of low intracellular Ca+ | High levels of calcium activate proteases

Question 32

Glutathionine uses up ____ of the ATP generated by glycolysis

Answer 32

11%

Question 33

The concentration in glutathione in cataracts

Answer 33

Is reduced

Question 34

Glutathione is a

Answer 34

Tripeptide (glycine-leucine-glutamic acid)

Question 35

GSH function

Answer 35

Protects sulhydryl groups (preventing aggregation via disulfide bonds) Protective against free radicals

Question 36

WHAT TRIGGERS OXIDATION?

Answer 36

Light

Question 37

Lens metabolism:

Answer 37

No mitochondria Low energy demands, consumes very little oxygen Mostly anaerobic-> poor amount of ATP

Question 38

Low oxygen tension around and within the lens helps

Answer 38

To protect lens proteins and lipids from oxidative damage

Question 39

Hydrogen peroxide can also be produced during

Answer 39

The oxidation of ascorbic acid, which is present in the aqueous and vitreous humor

Question 40

The lens is avascular so nutrients come from

Answer 40

Aqueous humor

Question 41

Lens behaves as a single cells

Answer 41

Syncytium

Question 42

In the lens Na+ ____ with age

Answer 42

Increases

Question 43

Calcium concentration on the lens is ____ than in the aqueous

Answer 43

50x less

Question 44

Healthy lens cell have

Answer 44

Low intracellular Ca+

Question 45

In cortical cataracts calcium is

Answer 45

16x higher

Question 46

The lens has a special amino acid called

Answer 46

Taurine who’s function is unknown

Question 47

Essential scavenger of free radicals

Answer 47

Ascorbic acid

Question 48

Protein synthesis in the lens

Answer 48

Does not exist, so you cant repair stuff

Question 49

Aerobic glycolysis is limited mostly to

Answer 49

Epithelium

Question 50

Pentose produces in HMP shunt can be used for DNA/RNA

Answer 50

Produces NADPH | Used in sorbitol path & glutathione reductase, fatty acid synthesis

Question 51

Phosphofructokinase

Answer 51

Determines how the glucose gets shunted

Question 52

Sorbitol increases

Answer 52

Osmotic concentration causing fluid influx into lens

Question 53

Decreased GSH means

Answer 53

Increased oxidation

Question 54

HMP shunt recreates glutathione

Answer 54

NADPH | Reduced glutathione

Question 55

What are free radicals

Answer 55

Molecules with odd number of electrons

Question 56

Enzymes involved in redox systems

Answer 56

Catalase Glutathione peroxidase Superoxidase dismutase Ascorbic acid

Question 57

When proteins in the lens precipitates

Answer 57

Lens color changes

Question 58

Ciliary muscles contact and lens bulges. This creates a greater curvature of the lens and more refraction of the light

Answer 58

Accommodation