Function And Physiology Of The Tear Film

Question 1

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

Answer 1

Dry eye syndrome

Question 2

Function of tear film

Answer 2

• 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

Question 3

Tear film structure from anterior to posterior

Answer 3

Lipid layer
Aqueous layer
Mucous layer

Question 4

Mucous layer and aqueous layer of the tear film

Answer 4

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

Question 5

Mucus layer composition

Answer 5

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

Question 6

High molecule weight glycoproteins that are heavily glycosylated

Answer 6

Mucin

Question 7

Two types of mucins

Answer 7

Membrane associated mucins

Secretory mucins.

Question 8

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

Answer 8

Membrane associated mucin

Question 9

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

Answer 9

Secretory mucins

Question 10

Function of mucus layer

Answer 10

• 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

Question 11

Sources of mucus for the mucus layer

Answer 11

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

Question 12

Aqueous layer composition

Answer 12

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

Question 13

What does sodium and chloride do in the aqueous layer

Answer 13

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

Question 14

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

Answer 14

Important for maintaining corneal epithelium health

Question 15

Osmaolrty and dry eye

Answer 15

Osmolarity increases with dry eye

-Na and CL

Question 16

Proteins of the aqueous layer

Answer 16

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

Question 17

Peptide growth factors in the aqueous layer

Answer 17

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

Question 18

Aqueous layer function

Answer 18

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

Question 19

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

Answer 19

3.5-10.5

Question 20

When does pH decrease in the tear film

Answer 20

During sleep

Question 21

When does pH increase in tear film

Answer 21

Dry eye due to osmolarity increase

Question 22

Function of aqueous layer

Answer 22

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

Question 23

Reflex and emotional tearing

Answer 23

Main lacrtimal gland

Question 24

Maintenance of tearing

Answer 24

Accessory lacrtimal gland

Question 25

Neural control of lacrimal glands

Answer 25

PNS, SNS, sensory nerves to main lacrimal gland PNS only: accessory lacrimal glands

Question 26

Lipid layer composition

Answer 26

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

Question 27

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

Answer 27

Polar surfactant phase of the lipid layer | Inner most layer of lipid layer

Question 28

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

Answer 28

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

Question 29

Lipid layer function

Answer 29

- 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

Question 30

Resources of lipid layer

Answer 30

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

Question 31

Tear distribution

Answer 31

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

Question 32

Clinical evaluation for tear secretion

Answer 32

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

Question 33

Clinical evaluation of tear film

Answer 33

- tear secretion - tear film stability - tear film osmolarity - lipid layer evaluation - ocular surface evaluation

Question 34

Tear deficiency dry eye

Answer 34

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

Question 35

Evaporating dry eye

Answer 35

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

Question 36

What is the resource of generating mucins in tear film

Answer 36

Goblet cells and squamous cells of cornea and conjunctiva

Question 37

What electrolytes are main contributor for osmolarity of tear film?

Answer 37

Na, CL

Question 38

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

Answer 38

Main lacrimal gland and accessory lacrimal gland

Question 39

Which layer is the major barrier to evaporation from ocular surface

Answer 39

Lipid layer

Question 40

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

Answer 40

Meibometry

Question 41

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

Answer 41

Tear deficient dry eye

Question 42

What tests do we do to test tear film stability

Answer 42

TBUT, ocular protection index, videokeratography, tear turnover

Question 43

What tests do we do to test tear film osmolarity

Answer 43

Tear film osmolarity, tear ferning, tear evaporation

Question 44

What tests do we do for lipid layer evaluation

Answer 44

Interferometry, meibometry

Question 45

What tests are used to test ocular surface eval

Answer 45

Flourescein, rose bengal, lisssamine green