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Physiology > Tear Film > Flashcards

Tear Film Flashcards

1
Q

What are functions of the precorneal tear film?

A

Provide a smooth optical surface at the air corneal interface

Allow diffusion of oxygen and other nutrients

Serve as a medium for removal of debris and protect the ocular surface

Provdies a medium for antimicrobial agents (lysozyme, lactoferrin and Iga)

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2
Q

What is the layers of the precorneal tear film? Thickness?

A

Lipid layer - 0.1um
Overlying
Mucoaqueous later
Aq (10um) , mucous (30um)

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3
Q

How thick is the human tear film?

A

3.4um

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4
Q

What are the functions of the lipid layer?

A

Retards evaporation of tear film

Contributes to the optical properties of the tear film because of its position at the air-tearfilm interface

Maintains hydrophobic barrier that prevents tear overflow by decreasing surface tension

Prevents damage tot he eyelid margin skin by tears

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5
Q

Where are the lipids secreted from? How may are there in each eyelid?

A

Meibomian glands

30-40 in the upper lid

20-30 in the lower lid

Sebaceous glands of Zeis - in the eyelid margin close to eyelash roots

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6
Q

Where do Meibomian glands open?

A

Eye lid margin between tarsal gray line and mucocutaneous junction

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7
Q

What are the functions of the mucoaqueous layer?

A

Transmits oxygen to the avascular corneal epithelium
Maintains a constant electrolyte composition over the ocular surface epithelium
Provides an antibacterial and antiviral defecse
Smooths minute irregularities of the anterior corneal surface
Modulates corneal and conjunctival epithelial cell function
Converts the corneal epitehlium from the hydrophobic to hydrophilic layer, which is essential for even and spontaneous distribution of the tear film
Interacts with the tear lipid layer to reduce sruface tension thereby stabilising the tear film
Lubcircates the eyelids as they pass over the globe

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8
Q

What are the two parts of the lacrimal gland

A

Orbital and palpebral lobes

By lateral horn of levator aponeurosis

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9
Q

What are glands of Krause? Where are they located?

A

2/3 of the accesory lacrimal glands
Located in the lateral part of upper fornix

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10
Q

Where are glands of Wolfring?

A

Along proximal margin of each tarsus

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11
Q

What does the aqueous component consist of? FUnctions?

A

Electrolytes:
- regulate osmotic flow of fluids, buffer tear pH, enzyme cofactors in controlling membrane permeability
Water
Proteins

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12
Q

What is the concentration of sodium and potassium in tear compare to blood?

A

Na same
K 5-7 times

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13
Q

What is used to dehydrate the cornea in corneal oedema?

A

Hypertonic saline

5%NaCl

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14
Q

What solutes are in tear film

A

Urea
Glucose
Lactate
Citrate
Ascorbate
Amino acids

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15
Q

What immunoglobulins are in tears?

A

IgA and secretory IgA

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16
Q

Where is IgA made?

A

Plasma cells in intersitital tissues of the main and accessory lacrimal galnds
Substantia propria of the conjunctiva

Secretory IgA in the lacrimal gland acini

17
Q

What is he function of IgA?

A

Local host defense mechanism of external eye

18
Q

What immunoglobulin is elecated in tear film in vernal conjunctivitis?

A

IgE

Increased IgE producing plasma cells in the giant papillae of the superior tarsal conjunctiva and elevated histamine levels

19
Q

Where is the mucin component of the mucoaq layer?

A

Coats the microplicae of the superficial corneal epithelial cells and forms a fine networs over the conjunctival surfaceW

20
Q

What does the mucin component contain?

A

Mucin
Proteins
Electrolytes
Water
Carbohydrates
Polar glycocalyx

21
Q

What are the types of mucins?

A

Secreted mucins - gel-forming and soluble, released into extracellular environment, secreted by goblet cells of conj

MEmbrane spanning mucins
Embedded in the lipid bilayer of cells, expressed by the stratified squamous cells of the conj and corneal epithelia

22
Q

What are mucins?

A

glycoproteins

23
Q

What is mucus discharge in DES? Infection? vernal conjunctivitis?

A

DES - stringy thin translucent

Infection - globular, crusting

vernal - thick, stretchy strands

24
Q

What are the stimuli of lacrimal secretion?

A

Neural tear secretion

Peptide hormones including alpha-MSH and ACRH stimulate protein secretion from main lacrimal gland

Steroid hormones - androgens, stimulate secretion of sIgA from the main lacrimal gland and lipid from the Meibomian glands

25
Q

How does blinking affect tear film?

A

Eyelids close in complete blink
Superior and inferior fornices are compressed by the force of the preseptal muscles
Eyelids move towards eachother
Upper eyelid moves over longer distance and exerts force on the globe

Force clears anteiror surface of debris and expresses Meibomian gland secretions

Lower eyelid moves nasally and pushes tear fluid toward the superior and inferior pucta

26
Q

What are diagnostic tests for tear dysfucntion?

A

Tear breakup time
Fluorescein staining
Lissamine green staining
Rose bengal staining
Osmolarity testing
Schiermer test
Tear meniscus evaluation
MMP-9 testing

27
Q

Where do postganglionic secretomotos fibres come from supplying lacrimal gland?

A

Pterygopalatine ganglion - hitchhike on zygomaticotemporal and lacrimal nervesH

28
Q

Hwo is reflex tearing mediated?

A

Parasympathetic nerves originating in superior salivatory nucleus stimulate myoepithelial cells lining lacrimal acini causing contraction

29
Q

What is average tearfilm break up time

A

10-30 seconds

30
Q

What does normal Schirmer test produce?

A

15-25mm of wetting over 5 minutes

31
Q

What is the osmolarity of aqueous layer and pH

A

About the same as normal sline pH 7.4

32
Q
A
33
Q

What is glucose conc of tear compare to plasma?

A

Lower as tear film supplies the corneal epithleium with glucose

34
Q

What is tear lipocalin?

A

20% of tear film protein
Protective effect on epithelium
Inhibtis cysteine proteinase
Cystatin also inhibits cysteint proteinase

35
Q

What type of gland is meibomian?

A

Holocrine

36
Q

What are the forms of tear film lipids?

A

Wax esters 32%
Sterol esters 27%
Free fatty acids 2%

Physiology (15 decks)

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