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Ocular Phys Block 11 > Physiology Of Hte Lens And Agigng Changes Of The Lens > Flashcards

Physiology Of Hte Lens And Agigng Changes Of The Lens Flashcards

1
Q

Anterior sutures

A

Upright Y

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2
Q

Posterior lens sutures

A

Upside down Y

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3
Q

Y sutures with age

A

More branches

Look like stars kinda

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4
Q

How much power does the lens provide

A

15D (1/3 of the total power)

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5
Q

What protects the retina from UV light

A

Lens

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6
Q

Lens composition

A

Water
Proteins
Others

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7
Q

Total lens proteins

A

Water soluble proteins (90%)

-crystallins, a, b, y

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8
Q

Alpha crystalline

A

Contributes to lens transparency and gives the lens a significantly higher RI than surrounding fluids

  • offers resistance to the degradation of the other crystalline, beta nad gamma, and is called the molecular chaperone
  • crystalline concentration varies among the lens, providing a refractive index gradient that is higher in the nucleus, than the outer cortical surface
  • SA in the lens is reduced due to the gradient index system and peripheral flattening
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9
Q

Transparency on a cellular level of the lens

A 
Small lens fibers 
Uniformity of the lens fibers
Regularity of packing 
Lack of organelles 
Avascular
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10
Q

Transparency at a molecular level of lens

A

Proteins are uniform
Proteins are small
Proteins concentration increases towards nucleus, creates RI gradient that is higher in nucleus, than the outer cortical space

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11
Q

Transparency: water in the lens

A

Water is pumped out of the lens from the anterior surface by Na/K pump

  • water enters the lens from the back because of osmotic pressure
  • we do not want water getting into the lens
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12
Q

Mitosis activity of the lens

A
  • mitosis of secondary fiber cells occurs in the germinative zone of the anterior lens epithelium
  • after mitosis, lens fiber cells gradually migrate through the transition zone and into the equator where elongation occurs
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13
Q

Protectors against oxidative damage in the lens

A

Glutathione

Ascorbic acid

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14
Q

Glutathione in the lens

A

-primary protector against oxidative damage in the lens
-transported in to the lens from the aqueous and can be synthesized from lens epithelial cells and superficial fiber cells
0detoxifies hydrogen peroxide

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15
Q

Ascorbic acid in the lens vs aqueous

A

Much higher in the lens

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16
Q

Aging changes in the lens

A

Cataracts and reduction of accommodation

17
Q

Ability of accommodation decreases by how much in presbyopia

A

Quarter of the age
40 yr old
15-(40x0.25)=5D

18
Q

Nuclear cataract

A
  • decline of glutathione, making the fibers susceptible to oxidative damage
  • older nuclea fiber lose organelles and their nucleus and gain yellow-brown pigment
19
Q

Age related cortical cataract

A
  • decreased glutathione activity, increases Ca2+, Na, and water
  • water forms lake, lakes separate cells, water vacuoles created, cause light scatter, cells burst, proteins exposed, proteins oxidized, cataracts are formed
20
Q

Posterior subcapsular cataract

A

-epithelial like cells migrate from the equatorial region and accumulate at the positerio pole forming an opacity

21
Q

Other lens aging changes

A 
Decrease in crystallins, esp alpha 
Thickens 
Radius of curvature decreases 
Decreases AA
Center of lens moves anterior with age
22
Q

Lens in diabetes

A

Diabetic cataract

  • insulin insensitive build up of blood glucose
  • increase in sorbitol production (hydrophilic)
  • increases osmotic pressure
  • increases water uptake
  • causes lens swelling
  • causes cataract formation
  • depletion of NADPH during sorbitol production
  • glutathione requires NADPH to reduce free radicals
  • oxidative stress
  • polymeriztion of proteins
23
Q

Refractive change in lens in diabetes

A

Change in osmolarity causes changes in

  • thickness
  • radius of curvature
  • Rx

Unusual changes in RX may indicate uncontrolled diabetes

24
Q

Unusual changes in RX may indicate

A

Uncontrolled diabetes

25
Q

The lens absorbs blue light the most to protect the retina, true or false

A

False

-protects from UV

26
Q

What type of proteins does the lens contain the most

A

Crystallins

27
Q

Where does Na/K pump located to help pumping out of water

A

Anterior epithelium

28
Q

What option below is the driving force of water entering the lens from the bac

A

Osmotic pressure

29
Q

Which part is responsible for formation of secondary lens fibers

A

Anterior epithelium

30
Q

What type of changes in lens are caused by accumulation of sorbitol

A

Cataracts and Rx changes

Ocular Phys Block 11 (6 decks)

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