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Anatomy and Biochemisty > Exam 1 Remington- Corneal Physiology > Flashcards

Exam 1 Remington- Corneal Physiology Flashcards

1
Q

What are the 4 functions of the cornea?

A

Transmits light, absorbs short wavelength UV, refracts light, and proper corneal function requires minimal scattering and distortion

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2
Q

Cornea scatters less than __% incident light.

A

1

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3
Q

Cytoplasm of epi and endo cells in the cornea contain what?

A

Corneal crystallins, water soluble proteins

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4
Q

What do corneal crystallins do?

A

They make cytoplasm homogenous and decrease light scattering

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5
Q

What range does the cornea transmit?

A

UV 310 nm to IR 2500 nm

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6
Q

What is the reason for photokeratitis?

A

The cornea absorbs short wavelength UV

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7
Q

Photokeratitis

A

Inflammation caused by absorption of UV

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8
Q

What are causes of photokeratitis?

A

Welder’s arc, tanning beds, and snowblindness

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9
Q

What is the refraction of light of the cornea determined by?

A

Curvatures of the various surfaces, interfaces between different indices of light, and length of pathway through the structures

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10
Q

Proper corneal function requires what?

A

Minimal scattering and distortion, no blood vessels, proper hydration

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11
Q

Relative corneal deturgescenes means the corneal is ___% water

A

78

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12
Q

Corneal hydration is dependent on what?

A

Temperature, swells when cooled and returns to normal at body temperature

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13
Q

What is the role of tears in maintaing proper hydration?

A

As tears evaporate the tear fluid becomes more concentrated, tear film osmolarity increases relative to the cornea, the hypertonicity of tear film draws water from cornea and the blink response is elicited because hypertonicity causes a slight sting and thus tear film is restored

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14
Q

What is the role of the epithelium in maintaining proper hydration?

A

ZO barrier prevents intercellular water influx from tears, ions move across both surfaces, aquaporins are water transport channels

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15
Q

What do channels of the epithelium allow?

A

Channels allows Na+ to pass into epi from tears and Cl- to pass into tears

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16
Q

What are major driving forces for water transport?

A

Cl- extrusion and Na+ influx

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17
Q

The co-transporter mechanism moves what ions in the cornea?

A

Na, K, and Cl ions

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18
Q

Na+/K+ ATPase pumps located in ______ ______ of the cornea actively move ions

A

Basolateral membrane

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19
Q

Aquarporins are present where?

A

Epithelial cell membranes

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20
Q

There is a ________ flow of water across the plasma membrane in the cornea.

A

Bidirectional

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21
Q

What is the role of the stroma in maintaining proper hydration?

A

GAGs are present in ground substance surrounding collagen fibers, increasing hydration leads to decreasing transparency

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22
Q

What is the role of GAGs in the stroma of the cornea?

A

Due to anionic characteristics they bind with water- there is an inherent tendency to imbibe water and to swell

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23
Q

Water content of the stroma should be approximately ___%

A

78

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24
Q

The normal water content of the sclera is ___%, if it falls below ___% or above ___% the sclera becomes lucent

A

68, 40, 80

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25
Q

What is the role of endothelium in the cornea in maintaining proper hydration?

A

These cells have high metabolic activity, apparent by large number of mitochondria and Golgi apparatus, slow leak of fluids and solutes from the aqueous, the Na+/K+ ATPase pump is located in the basolateral membrane of the endothelium

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26
Q

How does the Na+/K+ ATPase pump located in the basolateral membrane of the endothelium act?

A

Pumps act at a steady rate and the rate of leakage is dependent upon the pressure gradient across the endo

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27
Q

What are the ions that cotransporters move across membranes?

A

Na, K, Cl, HCO3

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28
Q

Where are aquaporins located in the endothelium?

A

In the endo cell membrane

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29
Q

What are 4 measures of endothelial function?

A

Coefficient of variation CV, cell density, polymegathism, and pleomorphism

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30
Q

What is the coefficient of Variation CV?

A

Indicates the degree of uniformity among endo cells

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31
Q

What is the CV equation?

A

Sd of mean cell area/ mean cell area

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32
Q

What is normal CV?

A

0.25

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33
Q

As CV increases there is an _____ in amount of variation in size

A

Increase

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34
Q

What is cell density?

A

Number of cells per unit area

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35
Q

How many cells in young?

A

4000-3000 cells/ mm^2 in young

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36
Q

How many cells by age 80?

A

2000 cell/ mm^2

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37
Q

How many cells necessary for normal function?

A

400-700

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38
Q

Polymegathism

A

Variation in cell size

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39
Q

Pleomorphism

A

Variation in cell shape

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40
Q

What is the most efficacious shape?

A

Hexagonal

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41
Q

Endothelial stress resulting from CL wear, disease, age, surgery etc. can lead to what?

A

Endothelial remodeling, including change in size, shape, or both

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42
Q

Corneal ATP is generated by what?

A

Glucose metabolism

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43
Q

Glucose enters cornea primarily from what?

A

Aqueous

44
Q

Oxygen enters cornea primarily from what?

A

Tear film

45
Q

In closed lid, oxygen is mostly from what?

A

Palpebral conj

46
Q

Utilizing anaerobic metabolism ~__ ATPs are produced per molecule of glucose

A

2

47
Q

Under aerobic conditions ~___ ATPs per molecule of glucose

A

36

48
Q

Cell proliferation includes what?

A

Nutrients, including glucose and amino acids

49
Q

Some glucose goes through the ____ ____ shunt providing building blocks for nucleic acid synthesis

A

Hexose monophosphate

50
Q

What are 2 manifestationss of corneal edema?

A

Change in dimension and change in appearance

51
Q

What happens when there is a change in dimension in corneal edema?

A

Diameter remains same, thickness increases

52
Q

How does the thickness increase in corneal edema?

A

Stromal matrix accumulates fluid, fiber diameter remains the same, swelling directed posteriorly, increase in corneal hydration positively linearly correlated with corneal thickness

53
Q

What is the change in appearance in corneal edema?

A

Normally ~1% light scattering, with fluid retention light scattering increases, cornea becomes cloudy, buckling of Descemet’s occurs and striae (folds) are seen

54
Q

What causes epithelial damage?

A

Loss of ZO, localized area of swelling and haziness, causes abrasion, injury

55
Q

What causes endothelial damage?

A

More serious, implies loss of active pump mechanism, caused by disease, surgery, injury, poorly fit contact lens may allow stagnation of tears

56
Q

What are 3 clinical manifestations of endothelial damage?

A

Formation of guttata, endothelial cells thin, and apical junctions deteriorate

57
Q

What is Fuch’s dystrophy?

A

Problem with cellular function, results in loss of endo function

58
Q

What are manifestations of Fuch’s dystrophy?

A

Guttata form, stromal edema, and epithelial microcysts

59
Q

What is metabolic edema?

A

Hypoxic condition causes an increase in anaerobic metabolism, concentration of lactate increases, osmotic balance changes and induces stromal edema

60
Q

What is the normal range of IOP?

A

10-20 mmHg

61
Q

What is borderline IOP?

A

21-25 mmHg

62
Q

What is high IOP?

A

> 25 mmHg

63
Q

What is very high IOP?

A

> 50 mmHg

64
Q

What happens with very high IOP?

A

Endo transport system overwhelmed, must be treated quickly

65
Q

What are 3 effects of corneal edema?

A

Hypoxia affects cellular function and causes decrease in intracellular pH, scarring can occur with dysfunction in collagen formation, neovascularization and new vessel growth

66
Q

What is acidification?

A

Cellular damage

67
Q

What is neovascularization?

A

Body’s defense mechanism to provide a source of O^2

68
Q

What is treatment of corneal edema?

A

Eliminate cause, temporary clearing with hypertonic solution of glycerin instillation

69
Q

Corneal injury induces activation of what molecules that initiate and direct corneal repair?

A

Integrins, cytokines, and growth factors

70
Q

Integrins

A

Facilitate and maintain cellular function

71
Q

Cytokines

A

Facilitate cellular communication

72
Q

Growth factors

A

Mediate proliferation and differentiation

73
Q

What happens in the epithelium in corneal wound healing?

A

Mitosis stops, cells at wound edges lose hemidesmosome attachments, basal cells migrate, when defect is covered protein synthesis increases, mitosis resumes and cell proliferation replaces lost cells, after the wound is healed hemidesmosomes reformed, cell membrane and BM are linked via a biochemical bond prior to reformation of hemidesmosomes, epithelium generally heals in 24-48 hours with hemidesmosomes reformed (usually no scarring evident)

74
Q

What happens when basal cells migrate in the epithelium?

A

Epidermal growth factor is released after injury and enhances cell migration and proliferation

75
Q

If BM injured, normal adhesion may take ___ months to be complete

A

12

76
Q

What happens to Bowman’s layer in corneal wound healing?

A

Cannot be regenerated, is replaced by epithelial or stromal tissue

77
Q

What happens to stroma in corneal wound healing?

A

Increase in number of keratocytes, collagen deposition in stroma, stromal healing not as rapid as epithelial healing

78
Q

What happens to collagen deposition in stroma during corneal wound healing?

A

Fiber arrangement not as regular, diameter of regenerated fibers is greater than normal, scar may result

79
Q

How long does stromal healing take?

A

May take up to 48 months for tensile strength to approach normal

80
Q

What happens in Descemet’s membrane during corneal wound healing?

A

Is very resistant to injury, will be secreted by the stromal fibroblasts and the endothelium

81
Q

What happens to endothelium during corneal wound healing?

A

Migration to cover area, cells thin and remodel into hexagonal shape, pump and barrier functions are reestablished

82
Q

What is the cause of neovascularization?

A

Disease, inflammation, or lack of oxygen

83
Q

New vessels sprout from what in corneal neoascularization?

A

Perilimbal capillaries

84
Q

What happens to the new vessels in corneal neovascularization?

A

Enzymes degrade BM of capillary, endothelial cells migrate, endothelial cells proliferate to form new vessels

85
Q

_____ _____ have been identified in the normal cornea

A

Antiangiogenic factors

86
Q

____ _____ are released in some diseases

A

Angiogenic factors

87
Q

What are ghost vessels?

A

Vessels do not resorb, but when the situation that produced them is reversed, they no longer carry blood

88
Q

Will ghost vessels be visible with slit lamp?

A

Yes

89
Q

Sensory nerves terminate in free nerve endings tightly surrounded by ____ ____

A

Epithelial cells

90
Q

Nerve ending pattern changes as the retract, reinsert or shift position apparently with ___ ___ ___

A

Epithelial cell turnover

91
Q

Sensory innervation is ____ times higher than any other epithelial tissue

A

400

92
Q

Sensory nerves have a ______ effect

A

Neurotrophic (influence corneal metabolism)

93
Q

In animal studies denervation be ablating ablating the ophthalmic division of the trigeminal leads to what?

A

Increased epithelial layer permeability, decreased cellular adhesion, impaired wound healing, reduced mitosis, and reduced cell migration

94
Q

What is the primary sensation in corneal sensitivity?

A

Pain

95
Q

Is corneal sensitivity high or low?

A

High

96
Q

Contact lenses _____ corneal sensitivity

A

Decreases

97
Q

How is corneal sensitivity clinically measured?

A

Blink response, atheiometer

98
Q

What is temperature corneal sensitivity like?

A

Registers changes but does not accurately recognize hot/cold

99
Q

In central corneal damage, normal nerve pattern is present by what week?

A

Week 4

100
Q

What happens in peripheral corneal damage?

A

Reinnervation takes longer than 60 days and density of pattern is lower than normal

101
Q

What type of fibers have been identified in the cornea?

A

Sympathetic

102
Q

The fibers in the cornea may affect what?

A

Cl ion channels

103
Q

Substances such as ______ and ______ have been identified in the cornea

A

Acetylcholine and acetylcholinesterase

104
Q

Why are acteylcholine and acetylcholinesterase in the cornea?

A

Transmitters for pain, contribute to tissue reaction that occurs in response to pain, mediate inflammatory response, play a role in transport processes and affect cellular permeability, regulate cell mitosis (perhaps because ACh can stimulate cGMP production and cGMP stimulates mitosis

105
Q

The sclera is a _____ tissue

A

Dynamic

106
Q

What happens in progressive myopia?

A

Collagen degradation, loss of proteoglycans, and changes in fibroblasts

Anatomy and Biochemisty (15 decks)

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