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Ocular Phys Block 12 > Function And Physiology Of The Tear Film > Flashcards

Function And Physiology Of The Tear Film Flashcards

1
Q

Disorder of the tear film caused by tear deficiency or excessive tear evaporation that causes damage to the interpalpebral ocular surface nad is associated with symptoms of ocular discomfort

A

Dry eye syndrome

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2
Q

Function of tear film

A
  • provides a smooth refractive surface for clear vision
  • maintins the health of corneal and conjunctival epithelial
  • acts as the first line of defense against microbial infections
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3
Q

Tear film structure from anterior to posterior

A

Lipid layer
Aqueous layer
Mucous layer

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4
Q

Mucous layer and aqueous layer of the tear film

A

They are sort of mixed together and have a gradient of mucins

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5
Q

Mucus layer composition

A

Intermost layer composed of mucin, immunoglobulins, urea, salts, glucose, leukocytes, cellular debris, and enzymes

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6
Q

High molecule weight glycoproteins that are heavily glycosylated

A

Mucin

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7
Q

Two types of mucins

A

Membrane associated mucins

Secretory mucins.

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8
Q

A dense barrier to pathogen penetrate, at the epithelial cell-tear film interface

A

Membrane associated mucin

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9
Q

Act as a cleaning crew, moving through the tear fluid and collecting debris that can be removed via the nsaolacrimal duct during blinking

A

Secretory mucins

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10
Q

Function of mucus layer

A
  • Maintain water on the surface fo the eye
  • The mucins also interact with tear lipids layer to lower surface tension thereby stabilizing the tear film
  • hydrophilic
  • provides lubircation for eyelid movement
  • traps exploited surface cell, foreign particles and bacteria
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11
Q

Sources of mucus for the mucus layer

A

Goblet cells and squamous cells of cornea and conjunctiva
Goblet cells major one

  • neural control
  • sensory nerves
  • PNS-increases secretion
  • SNS help regulate the goblet cell proliferation, not really to do with mucin increasing
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12
Q

Aqueous layer composition

A
  • composed of water, electrolytes, protein, peptides growth factors, vitamins, and hormones
  • middle layer
  • electrolytes include sodium, chloride, potassium, calcium
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13
Q

What does sodium and chloride do in the aqueous layer

A

Main contributors to osmolarity of tear film (osmolarity increases with dry eye)

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14
Q

What does potassium and calcium do to aqueous layer of the tear film

A

Important for maintaining corneal epithelium health

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15
Q

Osmaolrty and dry eye

A

Osmolarity increases with dry eye

-Na and CL

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16
Q

Proteins of the aqueous layer

A

Albumin, immunoglobulins (IgA) histamine, lactoferin, lysozyme, interleukins, antimicrboials

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17
Q

Peptide growth factors in the aqueous layer

A

EGF, TGF-B, HGF (hepatocyte grwoth facotr), and vitamin A

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18
Q

Aqueous layer function

A

Electrolytes act as a buffer to maintain a constant pH and contribute to maintaining epithelial integrity of the ocular surface

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19
Q

The buffer system of the aqueous layer of the tear film allows the eye to tolerate ophthalmic solution varying from ______ to _____ pH

20
Q

When does pH decrease in the tear film

A

During sleep

21
Q

When does pH increase in tear film

A

Dry eye due to osmolarity increase

22
Q

Function of aqueous layer

A

Offers strong defense system to protect against invading microorganism through contained proteins
-peptide growth factor and vitamin A act via auto rinse and paracrine mechanisms to regulate epithelial proliferation, motility and differentiation

23
Q

Reflex and emotional tearing

A

Main lacrtimal gland

24
Q

Maintenance of tearing

A

Accessory lacrtimal gland

25
Q

Neural control of lacrimal glands

A

PNS, SNS, sensory nerves to main lacrimal gland

PNS only: accessory lacrimal glands

26
Q

Lipid layer composition

A 
Outermost layer 
-meibomian oil 
-composed of two phases 
—polar surfactant phase
—nonmoral phase (overlaid polar phase)
27
Q

Primarily composed of phospholipids and glycilpids. Acts as a surfactant between the hydrophilic aqueous mucin layers and the thick, no polar lipid layer

A

Polar surfactant phase of the lipid layer

Inner most layer of lipid layer

28
Q

Primarily composed of wax, cholesterol esters, and trigs. Provides the air-tear film interface and is responsible for retarding evaporation

A

Nonpolar phase of the lipid layer (outermost layer of the lipid layer)

29
Q

Lipid layer function

A
  • major barrier to evaporation from the ocular surface
  • provides stability to the tear film through interactions with the aqueous mucin phase
  • provides a smooth optical surface fro the cornea
  • acts as a barrier against foreign particle
30
Q

Resources of lipid layer

A

Meibomian glands: with assistance by two other sebaceous glands, zeis and Moll

Neural control: PNS

31
Q

Tear distribution

A

Glycocalyx produced by the corneal epithelium helps bind the mucins to help tear film evenly distribute

32
Q

Clinical evaluation for tear secretion

A

Schirmer I, schirmer II, phenol red thread test, meinscometry

33
Q

Clinical evaluation of tear film

A
  • tear secretion
  • tear film stability
  • tear film osmolarity
  • lipid layer evaluation
  • ocular surface evaluation
34
Q

Tear deficiency dry eye

A

The largest category of dry eye. It occurs because of a disorder in lacrimal gland function, resulting in either reduced aqueous tear production and tear flow, to a failure to transfer lacrimal fluid into the conjunctival sac

35
Q

Evaporating dry eye

A

The lacrimal gland function is normal and the volume of lacrimal fluid is sufficient to cover the ocular surface, but another tear abs or agility exists that leads to increased tear evaporation

  • hyperosmolarity
  • meibomian gland disease
36
Q

What is the resource of generating mucins in tear film

A

Goblet cells and squamous cells of cornea and conjunctiva

37
Q

What electrolytes are main contributor for osmolarity of tear film?

38
Q

What is the resource of generating aqueous layer in tear film?

A

Main lacrimal gland and accessory lacrimal gland

39
Q

Which layer is the major barrier to evaporation from ocular surface

A

Lipid layer

40
Q

What clinical tests are used to eval the lipid layer in tear film?

A

Meibometry

41
Q

If there is a disorder in lacrimal gland function, what type of dry eye will be induced

A

Tear deficient dry eye

42
Q

What tests do we do to test tear film stability

A

TBUT, ocular protection index, videokeratography, tear turnover

43
Q

What tests do we do to test tear film osmolarity

A

Tear film osmolarity, tear ferning, tear evaporation

44
Q

What tests do we do for lipid layer evaluation

A

Interferometry, meibometry

45
Q

What tests are used to test ocular surface eval

A

Flourescein, rose bengal, lisssamine green

Ocular Phys Block 12 (5 decks)

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