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Ocular Physiology > Lens Final Info > Flashcards

Lens Final Info Flashcards

1
Q

lens scatters less then ___ % of incident light

A

5

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2
Q

how are the cells in the lens packed?

A

cells are densely packed resulting in destructive interference of scattered light

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3
Q

the different percentages of phospholipids in the cell membrane change as the cells age, resulting in:

A

a less fluid membrane (lens easier to rupture and scatter light)

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4
Q

3D change of membrane phospholipid example

A

the MIP of the gap junctions is cleaved from 26,000 dalton post-translational form to 22,000 dalton form

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5
Q

how are structural proteins of the lens affected by age?

A

the internal cell structure or the cytoskeleton of microtubules, actin, and intermediate filaments is gradually degraded as the cell ages

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6
Q

what occurs when the lens structural proteins are gradually lost?

A
  • without a cytoskeleton, the cell has difficulty maintaining its shape
  • old cells have less internal water and also shrink
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7
Q

what occurs to the crystallin proteins as the cell ages?

A

the crystallin proteins begin to clump together

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8
Q

initially the crystallin in a young lens are strongly associated with water, binding about ___ % of the water to the cell

A

24

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9
Q

with aging, the tertiary structure of the protein changes and less water ___ % is bound by the proteins

A

13

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10
Q

what is the overall result of crystallin proteins increasing aggregation in the lens? (and what is the term for it)

A

clumps of protein and pools of water (called syneresis) and light scatter

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11
Q

how is the water content of the lens affected by aging?

A

water no longer bound by proteins, osmolarity of lens decreases, water flows out of lens

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12
Q

cortical thickening rate of the lens with age is:

A

0.02 mm/ year

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13
Q

what is the result of cortical thickening of the lens with aging?

A

increased thickness of lens, nuclear fibers may not be able to get nourishment that they need from diffusion

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14
Q

explain the cataract changes on the synthesis of glutathione

A

concentration of glutathione decreases and the structural damage that results from UV and metabolic insult cannot always be repaired

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15
Q

explain the cataract changes on ion pumps

A
  • ion pumps become less effective
  • increased Na+, decreased K+ and amino acids
  • less protein synthesis
  • water control of lens harder
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16
Q

explain the cataract changes on metabolic activity

A

decrease in metabolic activity

  • fewer proteins made
  • less ATP available for normal functions
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17
Q

explain the cataract changes on crystallin proteins

A

crystallin proteins are oxidized and glycosylated, leading to cross-linking and insolubility

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18
Q

explain the cataract changes on metabolic breakdown

A

metabolic breakdown leads to:

  • osmotic imbalance
  • formation of vacuoles and clefts
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19
Q

explain the cataract changes on optical density

A

increased optical density leads to:

-color changes (brunescence) especially in nucleus

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20
Q

what causes an increase in optical density of the lens?

A

decrease in the water content of the lens

21
Q

the lens nucleus changes colors because of the :

A

breakdown of proteins

22
Q

explain the cataract changes causing opacities

A

-membranes rupture and accumulation of debris results in opacities

23
Q

_____ results in rupture of cell membranes

A

osmotic pressure

24
Q

cell membrane rupture results in

A

debris accumulation and light scatter- causing cataract

25
Q

when does diabetes mellitus usually cause a cataract?

A

usually 15-20 years after DM present unless it is very severe, uncontrolled case

26
Q

how high does the glucose concentration need to be in the aqueous to cause an increase in lens glucose concentration?

A

high > 175 mg/100mL

27
Q

describe how diabetes mellitus can cause “snowflake” opacities

A
  • high glucose causes osmotic imbalance which attracts water -> vacuoles form
  • if [glucose] goes down, vacuoles can disappear leaving snowflake opacities “punctate dot” cataracts
28
Q

other than causing an osmotic balance, what else can the excess glucose in the lens cause?

A
  • it also binds to proteins (glycosylation)

- it is converted to sorbitol which can accumulate

29
Q

what does glycosylation (excess glucose binding to proteins) result in:

A

causes protein aggregation, cross-linking, and insoluble proteins

30
Q

what is a galactosemic cataract?

A

from a galaxies breakdown issue- metabolic disease that has identical cataract appearance to diabetics

31
Q

a UV induced cataract (cortical in humans) from radiation cataract is a result of what cellular changes:

A
  • decreased glutathione, protein synthesis and sodium

- increased potassium

32
Q

type of cataract that has increased optical density in the nuclear portion of the lens and brunescent color

A

nuclear cataract

33
Q

type of cataract that is superficial to the nucleus

A

supranuclear cataract

34
Q

type of cataract that has opacities of the sutures

A

sutural cataract (very rare)

35
Q

type of cataract that is in the cortical region and can look like small dots, flecks, vacuoles, or vossius ring

A

cortical cataract (very common)

36
Q

type of cataract that is a side effect of anti-psychotic drug therapy (thorazine, phenylthiozine) that causes proliferation of epithelial cells

A

anterior subcapsular (rare)

37
Q

type of cataract that is a side effect of steroid use

A

posterior subcapsular (10% of all cataracts)

38
Q

type of cataract that looks like a spider web when viewed with a slit lamp and results from cellular proliferation or swelling at the equator

A

posterior subcapsular

39
Q

what type of migration occurs in posterior sub capsular cataract?

A

abnormal migration to the posterior pole from equator

40
Q

this cataract results in the greatest loss of vision of any cataract

A

posterior subcapsular

41
Q

the accommodative response requires about ___ ms to initiate

A

350 msec

42
Q

explain the changes that occur when the ciliary muscle contracts

A

decreased tension on zonules, lens becomes more spherical, increase in dioptric power

43
Q

ciliary muscle contraction causes what movements of the lens

A
  • lens moves forward (decreasing depth of anterior chamber)

- lens sinks a little (gravity effects)

44
Q

ciliary muscle contraction causes what IOP change

A

IOP rises momentarily and then decreases

45
Q

ciliary muscle contraction causes what change in circumference of the lens

A

circumference of the equator of the lens decreases

46
Q

ciliary muscle contraction causes what surface of the lens to change shape the most?

A

front surface of lens

47
Q

even though all accommodation is generally lost by age 50, what still is present?

A

depth of focus (1-2 D)

48
Q

4 potential causes of presbyopia

A
  1. hardening of the lens
  2. weakening of ciliary muscle
  3. enlargement of the lens
  4. loss of capsule elasticity

Ocular Physiology (8 decks)

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