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Ocular Physiology > Tear Film > Flashcards

Tear Film Flashcards

1
Q

Tear film function

A
  • Wound healing
  • access route for leukocytes
  • electrolytes for metabolism
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2
Q

Tear film provides pathway for ___ in case of injury

A

WBC

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3
Q

3 layers of the tear film

A

Oily, aqueous, and mucus

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4
Q

Function of oily layer of tear film

A

Smoothing the tear surface and reducing evaporation of tears

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5
Q

Outermost layer of the tear film

A

Oily layer

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6
Q

Function of aqueous layer of the tear film

A

Cleanses the eye and washes always foreign particles or irritants

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7
Q

Inner layer of the tear film

A

Mucus

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8
Q

Mucus layer of the tear film is produced by

A

Goblet cells of the conjunctiva

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9
Q

Function of mucus layer of the tear film

A

Allows the watery layer to spread evenly over the surface of the eye and helps remain moist

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10
Q

How are tears produced (2 ways)?

A

Basal and reflex secretion

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11
Q

When the eye is irritated, the lacrimal gland produces

A

A large volume of tears that can overwhelm the tear drainage system and overflow from your eye

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12
Q

What is basal secretion?

A

Slow, continuous tear secretion responsible for normal eye lubrication

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13
Q

Basal secretion is secreted by the

A

Accessory glands

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14
Q

What is reflex/ excessive secretion?

A

Large quantities of tears in response to eye irritation (foreign particles) or emotions

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15
Q

Reflex secretion is secreted by

A

The main lacrimal gland

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16
Q

How does a healthy tear film spread

A

Across the eye by a blink

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17
Q

Without an adequate tear film

A

Sharp vision isn’t possible

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18
Q

What is the pH of tears

A

7.4

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19
Q

When the eye is open, tears secreted provide the bulk of ____ and nutrients in their secretions and remove___

A

Provide O2 and remove CO2

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20
Q

When the eye is closed, the aqueous humor,

A

Bathes the endothelial side of the cornea, supplies the cornea with most of the metabolic needs

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21
Q

Tear pH is maintained around 7.14-7.82 by buffers that are mainly. If pH is too low/high there will be ___.

A

Bicarbonate, H+, and proteins

Irritation of the eye

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22
Q

Tear osmolarity is usually 308-316 mOsms/L similar to

A

Plasma

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23
Q

A small increase of 10 mOsm in the tear film is enough to

A

Be deleterious to the ocular surface

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24
Q

What ions to tears contain

A

Na+, K+, Cl+, HCO3-, Ca2+, Mg2+

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25
Q

Tears ion concentration compares to plasma

A

Higher K+, CL-, and similar Na+

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26
Q

The proteins in tears are secreted by

A

Orbital glands

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27
Q

Do tears normally contain serum proteins?

A

Not usually but they can enter the tears from leaky conjunctiva blood vessels under pathological conditions

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28
Q

Most important function of the tear film

A

Preventing bacterial and viral infections

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29
Q

Major antibacterial tear proteins are

A

Lysozyme, secretory immunoglobulin IgA, lactoferrin, lipocalin amd peroxidase

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30
Q

What is the most abundant protein in the tear film

A

Albumin

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31
Q

Mucin entrap and remove

A

Irritants

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32
Q

Glycoproteins

A

In mucin , antibacterial and antiviral

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33
Q

Mucin protect the underlying epithelial cells by

A

Binding to and entrapping bacteria and viruses

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34
Q

Mucin carbohydrate side chains are ____ and are able to bind to a wide variety of microorganisms

A

Heterogenous

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35
Q

Mucin binding to bacteria and viruses prevent

A

Them from attaching to the ocular surface and invading it

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36
Q

The lipid layer is formed by polar and neutral lipid that face

A

The aqueous amd non polar face the air

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37
Q

The oily layer of the tear film prevents

A

Overflow of tears and retards their evaporation

Migration of skin lipids onto the ocular surface

Contamination

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38
Q

Cauterization (removing) of the orifices of meibomian glands increase

A

Evaporation by more than 10 times and results in absence of oily laye

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39
Q

The lipid layer acts as a surfactant layer which

A

Makes an effective bridge between the non polar lipid phase and aqueous mucinous phase

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40
Q

Lipid layer acts as a lubricant to

A

Facilitate smooth movement of eyelids during blinking

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41
Q

Aqueous layer is secreted by

A

Lacrimal glands and accessory of Krause and wolfring

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42
Q

What makes 60% of the tear film

A

Aqueous layer

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43
Q

At low flow rates of the aqueous layer its ___ and at high it becomes ___

A

Hypertonic , isotonic

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44
Q

Mucus layer is made of

A

Epithelial cell glycocalyx and glycoprotein , mixed with lipids , anchored by micro Viti

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45
Q

Main tear mucin

A

MUC5AC

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46
Q

Clear corneal epithelium is a

A

Hydrophobic surface

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47
Q

For tears to cover cornea completely the surface must be

A

Converted to hydrophilic surface

48
Q

What are glycocalyx

A

Long chain of molecules that help hold mucin to the corneal surface

49
Q

How does glycocalyx migrate

A

Out from the surface of the corneal microvilli to form a hydrophilic network that holds mucin on the ocular surface

50
Q

Holding mucin to the ocular surface creates

A

A water attraction , as well as protection against pathogens

51
Q

THE OCULAR SURFACE ORGANS ARE LONKED TO NEURAL REFLEX ARC VIA THE _____ AND THE _____

A

AFFERENT SENSORY CRANIAL NERVE V (TRIGEMINAL) AND

EFFERENT MOTOR FIBERS OF CRANIAL NERVE VII (FACIAL)

52
Q

CNV SENSORY ___

CNVII ___

A

CNV INPUT

CNVII OUTPUT

53
Q

Neural pathways from __ and ___ control meibomian, lacrimal and goblet cells

A

Sphenopalantine ganglion and superior cervical ganglion

54
Q

CNV bears the ___ pathway of the tear reflexes

A

Afferent / sensory

55
Q

The motor pathway of the tear film is involuntary using

A

CNVII in parasympathetic division as an efferent pathways

56
Q

Irritation stimulus typically increases

A

Lacrimal gland secretion/ blinking/ for protective eye closure or renew tear film

57
Q

The function of ocular surfaces and particularly of the glands are influenced by

A

Androgens in both sexes

58
Q

Females have a high risk for dry eye because

A

Lower level of androgens

Menopause can disturb function of ocular surface (low estrogen during menopause_

59
Q

Androgen sex steroids regulate

A

meibomian gland lipid synthesis and secretion

60
Q

The nerve fibers of the meibomian gland are mainly positive for ___ and are hence supposed to represent a part of the ___ nervous system

A

Acetylcholinerase

Cholinergic parasympathetic nervous system

61
Q

Androgens are potent hormones that stimulate secretion of

62
Q

Primary input of innervation for lacrimal glands

A

Parasympathetic innervation provides the primary input

63
Q

___ sensory nerves innervate the lacrimal gland

A

Parasympathetic, sympathetic, and sensory nerves

64
Q

Whats crocodile tears syndrome

A

Due to injury of facial nerve proximal to the geniculate ganglion-> patient lacrimates while chewing

65
Q

Tear film proteins

A

Lysozyme
Lactoferrin and transferrin
IgA

66
Q

IgA

A

Major antibody present in serimucous secretions

67
Q

Lysozyme

A

Degrades cell wall bacteria succumbs to osmotic gradient

68
Q

Evidence suggests that the concentration of EGF is ____ in dry eye syndrome

69
Q

Peptide growth factors and vitamin A are involved in

A

epithelial proliferation, motility, and differentiation

70
Q

Tear film washes away

A

Debri and microorganisms

71
Q

Allows the water layer to spread every over the surface of the eye and helps maintain eye moist

A

Mucus inner layer

72
Q

Lipid layer is derived from

A

Meibomian glands

Zeiss and moll

73
Q

If lipid layer isn’t working properly you will get

74
Q

Villi in epithelium layer is very lipophilic/ hydrophobic so

A

Mucin layer is added so water is allowed to get there and sit

75
Q

Tear film is a complex mixture that mimics

76
Q

Peptide growth factors involved in corneal

A

Wound healing and immune modulation

77
Q

Trefoil factor family (TFF) can interact with

A

Mucin, and thereby mucus viscosity

78
Q

Patients suffering from dry eye contained significantly higher

A

TFF3 compared to healthy volunteers

79
Q

Lipid movement along ducts os facilitated by contractions of o.o. (Blink). In bell’s palsy

A

Lid doesnt blink properly so it will affect oil being secreted and cause patient to have dry eye

80
Q

Holocrine

A

Lipid secretion : rupture of secretory cell releases droplets/ debris into duct

81
Q

Polar lipids are found in oily layer

A

Surfactant interface between aqueous and hydrophobic non polar lipids that form bulk of oily layer

82
Q

Surface tension determines

A

Wetting power of tears on corneal surface

83
Q

Ability of meibomian oil to spread over film depend on

A

Liquid surface tension component as it relates to “spreading” coefficient

84
Q

Lipocalin may contribute to a stable tear film but

A

Interacting with the meibomian lipids

85
Q

Lipocalin, a lipid-binding protein, scavenges

A

Potentially harmful hydrophobic molecules

86
Q

Lipocalin may be responsible for

A

High viscosity,low surface tension

87
Q

Lipocalin can inhibit bacterial and fungal infections by

A

Working with iron chelating compounds (lactoferrin)

88
Q

Melting theory

A

Meibomian forms a liquid at ocular surface temp. If it does not tears will evaporate and you will have a dry eye, hot compresses are used

89
Q

In their normal state, meibomian secretions are

90
Q

Meibomian seborrhea

A

Oily skin, prone to have oil glands plugged (hypersecretory meibomian disease) MGD

91
Q

Obstructive/hyposecretory MGD

A

People with dry skin
-difficult to express the lipids in these patients
(Glands are scared shut)

92
Q

Hot compress to treat MGD

A

Can liquify inspissated oil

93
Q

Disruptions of lipid layer leads to decrease TBUT which will lead to

A

Clinical dry eye

94
Q

Lipid layer prevents overflow of tears at lid marking by

A

Providing local hydrophobic barrier

95
Q

Key outcome of having plugged oil glands (blepharitis, meibomitis, rosacea)

A

Evaporation

96
Q

Chronic decrease blinking

A

(Gamers)

Creates plugging of the MG orifice.

97
Q

If a pt has dry eyes the tears are going to break up quicker so

A

They will blink a lot because of unprotected ocular surface and ocular discomfort

98
Q

Hordeolum and chalazion

A

Happen when there’s build up lipid

99
Q

Chalazion are mainly

A

Scar tissue so harder to manage

Not painful

100
Q

Hordeolum is an

A

Infectious process aka stye

Painful!

101
Q

Doxycycline and azithromycin

A

Used to treat hordeolum and chalazion

102
Q

When you have evaporative dry eye you will have low TBUT and normal Schirmer test (normal bc)

A

Because it measures tear out put

103
Q

Blepharitis causes tear film disruptions

A

PA2 induces release of histamines, prostaglandin and serotonin

104
Q

Hormones involved in tear film problems

A

Estrogen, testosterone, prolactin

105
Q

Autoimmune disorders could cause dry eye

A

Lacrimal gland dysfunction (sjorgren’s syndrome)

106
Q

Mucin and the secreted glycocalyx (which consists of glycoproteins) are

A

Absorbed by the epithelium of the cornea to convert it from a hydrophobic into a wettable hydrophilic surface

107
Q

In some CL lens wearers, collapsed mucin, lipids, and tear proteins will build up behind the CL and from small balls

A

Mucin balls/plugs

Don’t cause discomfort or loss of vision

108
Q

A damaged glycocalyx exposes the epithelial cell, resulting in a loss of microvilli. Once exposed

A

The corneal surface loses the protection of an intact tear film

109
Q

Lack of mucin will cause tears to

110
Q

Goblet cells have

A

M2 & M3 muscarinic receptors

111
Q

Loss of goblet cells is associated with

A

Dry eye disease and certain autoimmune disorders that affect the eye

112
Q

Just like the tear film, blinking moves the mucin

113
Q

Rare diseases like Vit A deficiency , Steven Johnson’s syndrome and ocular cicatricial pemphigoid (OCP) will lead to

A

Less mucin

114
Q

Loss of tight junctions leads to

A

Accelerated epithelial desquamation, cornea barrier disruption and exposure of cornea pain

115
Q

Dry eye can trigger immune response with

A

Increased osmolarity

Ocular Physiology (7 decks)

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