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Ocular Physiology Exam 2 > Lens > Flashcards

Lens Flashcards

1
Q

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

A

Focus on objects that’s are near or far

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2
Q

Lens vascularization and innervation

A

Lens is avascular and no innervation

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3
Q

What is vossius ring?

A

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

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4
Q

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

A

Purely epithelial structure

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5
Q

The oldest cells of the lens are located

A

In the center of the lens

Youngest are always on the surface

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6
Q

Small cuts and tears in the lens capsule will result in

A

Lens opacities

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7
Q

The lens capsule is more fragile in

A

Diabetics

Having too much sugar makes the capsule weaker

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8
Q

Lens capsule is secreted by

A

The basal cell area of the lens epithelium

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9
Q

Lens is like an onion because ___ which affects ____.

A

New layers are added over a pts life span

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

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10
Q

Active layer of the lens is

A

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

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11
Q

The bulk of the lens is composed of

A

Lens fiber

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12
Q

Mitotic cells ___ with age

A

Decrease

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13
Q

What layer is the most susceptible to radiation damage ?

A

Epithelial cells

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14
Q

Mature lens fibers are cells which

A

Have lost their nuclei

Eliminates light scatter

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15
Q

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

A

Syncytium

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16
Q

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

A

The lens nuclei would create light scatter and distort retinal images

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17
Q

Epithelial transitions to

A

Fiber cell

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

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18
Q

Lens sutures

A

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

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19
Q

Zonules are primary made of

A

Fibrillin, a connective tissue protein

Contain cysteine

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20
Q

In Marfans syndrome

A

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

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21
Q

What is ectopic lentis

A

Lens dislocation/ subluxation

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

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22
Q

Hydration of the lens

A

Relatively dehydrated organ

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

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23
Q

The majority of the lens protein is

A

Structural protein/ crystallin

Water soluble

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24
Q

Most insoluble proteins are found in

A

The lens nucleus / oldest part of the eye

25
Q

Solubility decreases with age

A

Why we see cataracts on older people

26
Q

Water soluble structural proteins

A

Crystallins

27
Q

Crystallins are chaperones

A

Provides lens with oxidative stress resistant properties (chaperone like activity)

They also prevent aggregation

28
Q

When crystallin become insoluble

A

Light scatter occurs

29
Q

Oxidation releases

A

Free radicals that tear up membranes

30
Q

Glutathione (GSH synthesis)

A

Important in lens, tries to minimize damage form oxidation

31
Q

A way to keep lens transparent is by

A

Maintainance of low intracellular Ca+

High levels of calcium activate proteases

32
Q

Glutathionine uses up ____ of the ATP generated by glycolysis

A

11%

33
Q

The concentration in glutathione in cataracts

A

Is reduced

34
Q

Glutathione is a

A

Tripeptide (glycine-leucine-glutamic acid)

35
Q

GSH function

A

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

36
Q

WHAT TRIGGERS OXIDATION?

A

Light

37
Q

Lens metabolism:

A

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

38
Q

Low oxygen tension around and within the lens helps

A

To protect lens proteins and lipids from oxidative damage

39
Q

Hydrogen peroxide can also be produced during

A

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

40
Q

The lens is avascular so nutrients come from

A

Aqueous humor

41
Q

Lens behaves as a single cells

A

Syncytium

42
Q

In the lens Na+ ____ with age

A

Increases

43
Q

Calcium concentration on the lens is ____ than in the aqueous

A

50x less

44
Q

Healthy lens cell have

A

Low intracellular Ca+

45
Q

In cortical cataracts calcium is

A

16x higher

46
Q

The lens has a special amino acid called

A

Taurine who’s function is unknown

47
Q

Essential scavenger of free radicals

A

Ascorbic acid

48
Q

Protein synthesis in the lens

A

Does not exist, so you cant repair stuff

49
Q

Aerobic glycolysis is limited mostly to

A

Epithelium

50
Q

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

A

Produces NADPH

Used in sorbitol path & glutathione reductase, fatty acid synthesis

51
Q

Phosphofructokinase

A

Determines how the glucose gets shunted

52
Q

Sorbitol increases

A

Osmotic concentration causing fluid influx into lens

53
Q

Decreased GSH means

A

Increased oxidation

54
Q

HMP shunt recreates glutathione

A

NADPH

Reduced glutathione

55
Q

What are free radicals

A

Molecules with odd number of electrons

56
Q

Enzymes involved in redox systems

A

Catalase
Glutathione peroxidase
Superoxidase dismutase
Ascorbic acid

57
Q

When proteins in the lens precipitates

A

Lens color changes

58
Q

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

A

Accommodation

Ocular Physiology Exam 2 (4 decks)

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