Tear Film Flashcards
1
Q
Tear film function
A
- Wound healing
- access route for leukocytes
- electrolytes for metabolism
2
Q
Tear film provides pathway for ___ in case of injury
A
WBC
3
Q
3 layers of the tear film
A
Oily, aqueous, and mucus
4
Q
Function of oily layer of tear film
A
Smoothing the tear surface and reducing evaporation of tears
5
Q
Outermost layer of the tear film
A
Oily layer
6
Q
Function of aqueous layer of the tear film
A
Cleanses the eye and washes always foreign particles or irritants
7
Q
Inner layer of the tear film
A
Mucus
8
Q
Mucus layer of the tear film is produced by
A
Goblet cells of the conjunctiva
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
10
Q
How are tears produced (2 ways)?
A
Basal and reflex secretion
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
12
Q
What is basal secretion?
A
Slow, continuous tear secretion responsible for normal eye lubrication
13
Q
Basal secretion is secreted by the
A
Accessory glands
14
Q
What is reflex/ excessive secretion?
A
Large quantities of tears in response to eye irritation (foreign particles) or emotions
15
Q
Reflex secretion is secreted by
A
The main lacrimal gland
16
Q
How does a healthy tear film spread
A
Across the eye by a blink
17
Q
Without an adequate tear film
A
Sharp vision isn’t possible
18
Q
What is the pH of tears
A
7.4
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
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
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
22
Q
Tear osmolarity is usually 308-316 mOsms/L similar to
A
Plasma
23
Q
A small increase of 10 mOsm in the tear film is enough to
A
Be deleterious to the ocular surface
24
Q
What ions to tears contain
A
Na+, K+, Cl+, HCO3-, Ca2+, Mg2+
25
Tears ion concentration compares to plasma
Higher K+, CL-, and similar Na+
26
The proteins in tears are secreted by
Orbital glands
27
Do tears normally contain serum proteins?
Not usually but they can enter the tears from leaky conjunctiva blood vessels under pathological conditions
28
Most important function of the tear film
Preventing bacterial and viral infections
29
Major antibacterial tear proteins are
Lysozyme, secretory immunoglobulin IgA, lactoferrin, lipocalin amd peroxidase
30
What is the most abundant protein in the tear film
Albumin
31
Mucin entrap and remove
Irritants
32
Glycoproteins
In mucin , antibacterial and antiviral
33
Mucin protect the underlying epithelial cells by
Binding to and entrapping bacteria and viruses
34
Mucin carbohydrate side chains are ____ and are able to bind to a wide variety of microorganisms
Heterogenous
35
Mucin binding to bacteria and viruses prevent
Them from attaching to the ocular surface and invading it
36
The lipid layer is formed by polar and neutral lipid that face
The aqueous amd non polar face the air
37
The oily layer of the tear film prevents
Overflow of tears and retards their evaporation
Migration of skin lipids onto the ocular surface
Contamination
38
Cauterization (removing) of the orifices of meibomian glands increase
Evaporation by more than 10 times and results in absence of oily laye
39
The lipid layer acts as a surfactant layer which
Makes an effective bridge between the non polar lipid phase and aqueous mucinous phase
40
Lipid layer acts as a lubricant to
Facilitate smooth movement of eyelids during blinking
41
Aqueous layer is secreted by
Lacrimal glands and accessory of Krause and wolfring
42
What makes 60% of the tear film
Aqueous layer
43
At low flow rates of the aqueous layer its ___ and at high it becomes ___
Hypertonic , isotonic
44
Mucus layer is made of
Epithelial cell glycocalyx and glycoprotein , mixed with lipids , anchored by micro Viti
45
Main tear mucin
MUC5AC
46
Clear corneal epithelium is a
Hydrophobic surface
47
For tears to cover cornea completely the surface must be
Converted to hydrophilic surface
48
What are glycocalyx
Long chain of molecules that help hold mucin to the corneal surface
49
How does glycocalyx migrate
Out from the surface of the corneal microvilli to form a hydrophilic network that holds mucin on the ocular surface
50
Holding mucin to the ocular surface creates
A water attraction , as well as protection against pathogens
51
THE OCULAR SURFACE ORGANS ARE LONKED TO NEURAL REFLEX ARC VIA THE _____ AND THE _____
AFFERENT SENSORY CRANIAL NERVE V (TRIGEMINAL) AND
| EFFERENT MOTOR FIBERS OF CRANIAL NERVE VII (FACIAL)
52
CNV SENSORY ___
| CNVII ___
CNV INPUT
| CNVII OUTPUT
53
Neural pathways from __ and ___ control meibomian, lacrimal and goblet cells
Sphenopalantine ganglion and superior cervical ganglion
54
CNV bears the ___ pathway of the tear reflexes
Afferent / sensory
55
The motor pathway of the tear film is involuntary using
CNVII in parasympathetic division as an efferent pathways
56
Irritation stimulus typically increases
Lacrimal gland secretion/ blinking/ for protective eye closure or renew tear film
57
The function of ocular surfaces and particularly of the glands are influenced by
Androgens in both sexes
58
Females have a high risk for dry eye because
Lower level of androgens
Menopause can disturb function of ocular surface (low estrogen during menopause_
59
Androgen sex steroids regulate
meibomian gland lipid synthesis and secretion
60
The nerve fibers of the meibomian gland are mainly positive for ___ and are hence supposed to represent a part of the ___ nervous system
Acetylcholinerase
Cholinergic parasympathetic nervous system
61
Androgens are potent hormones that stimulate secretion of
IgA
62
Primary input of innervation for lacrimal glands
Parasympathetic innervation provides the primary input
63
___ sensory nerves innervate the lacrimal gland
Parasympathetic, sympathetic, and sensory nerves
64
Whats crocodile tears syndrome
Due to injury of facial nerve proximal to the geniculate ganglion-> patient lacrimates while chewing
65
Tear film proteins
Lysozyme
Lactoferrin and transferrin
IgA
66
IgA
Major antibody present in serimucous secretions
67
Lysozyme
Degrades cell wall bacteria succumbs to osmotic gradient
68
Evidence suggests that the concentration of EGF is ____ in dry eye syndrome
Decrease
69
Peptide growth factors and vitamin A are involved in
epithelial proliferation, motility, and differentiation
70
Tear film washes away
Debri and microorganisms
71
Allows the water layer to spread every over the surface of the eye and helps maintain eye moist
Mucus inner layer
72
Lipid layer is derived from
Meibomian glands
| Zeiss and moll
73
If lipid layer isn’t working properly you will get
A dry eye
74
Villi in epithelium layer is very lipophilic/ hydrophobic so
Mucin layer is added so water is allowed to get there and sit
75
Tear film is a complex mixture that mimics
Serum
76
Peptide growth factors involved in corneal
Wound healing and immune modulation
77
Trefoil factor family (TFF) can interact with
Mucin, and thereby mucus viscosity
78
Patients suffering from dry eye contained significantly higher
TFF3 compared to healthy volunteers
79
Lipid movement along ducts os facilitated by contractions of o.o. (Blink). In bell’s palsy
Lid doesnt blink properly so it will affect oil being secreted and cause patient to have dry eye
80
Holocrine
Lipid secretion : rupture of secretory cell releases droplets/ debris into duct
81
Polar lipids are found in oily layer
Surfactant interface between aqueous and hydrophobic non polar lipids that form bulk of oily layer
82
Surface tension determines
Wetting power of tears on corneal surface
83
Ability of meibomian oil to spread over film depend on
Liquid surface tension component as it relates to “spreading” coefficient
84
Lipocalin may contribute to a stable tear film but
Interacting with the meibomian lipids
85
Lipocalin, a lipid-binding protein, scavenges
Potentially harmful hydrophobic molecules
86
Lipocalin may be responsible for
High viscosity,low surface tension
87
Lipocalin can inhibit bacterial and fungal infections by
Working with iron chelating compounds (lactoferrin)
88
Melting theory
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
In their normal state, meibomian secretions are
Clear
90
Meibomian seborrhea
Oily skin, prone to have oil glands plugged (hypersecretory meibomian disease) MGD
91
Obstructive/hyposecretory MGD
People with dry skin
-difficult to express the lipids in these patients
(Glands are scared shut)
92
Hot compress to treat MGD
Can liquify inspissated oil
93
Disruptions of lipid layer leads to decrease TBUT which will lead to
Clinical dry eye
94
Lipid layer prevents overflow of tears at lid marking by
Providing local hydrophobic barrier
95
Key outcome of having plugged oil glands (blepharitis, meibomitis, rosacea)
Evaporation
96
Chronic decrease blinking
(Gamers)
| Creates plugging of the MG orifice.
97
If a pt has dry eyes the tears are going to break up quicker so
They will blink a lot because of unprotected ocular surface and ocular discomfort
98
Hordeolum and chalazion
Happen when there’s build up lipid
99
Chalazion are mainly
Scar tissue so harder to manage
| Not painful
100
Hordeolum is an
Infectious process aka stye
| Painful!
101
Doxycycline and azithromycin
Used to treat hordeolum and chalazion
102
When you have evaporative dry eye you will have low TBUT and normal Schirmer test (normal bc)
Because it measures tear out put
103
Blepharitis causes tear film disruptions
PA2 induces release of histamines, prostaglandin and serotonin
104
Hormones involved in tear film problems
Estrogen, testosterone, prolactin
105
Autoimmune disorders could cause dry eye
Lacrimal gland dysfunction (sjorgren’s syndrome)
106
Mucin and the secreted glycocalyx (which consists of glycoproteins) are
Absorbed by the epithelium of the cornea to convert it from a hydrophobic into a wettable hydrophilic surface
107
In some CL lens wearers, collapsed mucin, lipids, and tear proteins will build up behind the CL and from small balls
Mucin balls/plugs
| Don’t cause discomfort or loss of vision
108
A damaged glycocalyx exposes the epithelial cell, resulting in a loss of microvilli. Once exposed
The corneal surface loses the protection of an intact tear film
109
Lack of mucin will cause tears to
Bead up
110
Goblet cells have
M2 & M3 muscarinic receptors
111
Loss of goblet cells is associated with
Dry eye disease and certain autoimmune disorders that affect the eye
112
Just like the tear film, blinking moves the mucin
Nasally
113
Rare diseases like Vit A deficiency , Steven Johnson’s syndrome and ocular cicatricial pemphigoid (OCP) will lead to
Less mucin
114
Loss of tight junctions leads to
Accelerated epithelial desquamation, cornea barrier disruption and exposure of cornea pain
115
Dry eye can trigger immune response with
Increased osmolarity
