Tears

Question 1

tear film functions

Answer 1

1. trapping debris and helps remove sloughed cells and debris
2. keeping surface of the cornea moist and acts as a lubricant between the globe and eyelids
3. primary source of oxygen and nutrients for the cornea
4. helps maintain corneal hydration by preventing evaporation
5. it aids in corneal healing by providing the necessary substances
6. it provides a smooth refractive surface necessary for optical function
7. it contains antibacterial substances to help protect against infection

Question 2

what is the primary source of oxygen and nutrients for the cornea?

Answer 2

the tear film

Question 3

eyelids and conjunctiva

Answer 3

add protection the the cornea

Question 4

conjunctiva

Answer 4

lines the upper and lower eyelids

Question 5

ciliary body

Answer 5

it creates a sac over lying the cornea, limbus and iris

protects the cornea while acting as a fluid reservoir

Question 6

lid and lashes

Answer 6

protect the exposed surface of the eyes

- well developed blink response to irritants, which traps foreign bodies so they can be washed away

Question 7

what is the tear film

Answer 7

this is an 8-10 micrometer protective covering for the cornea made of 3 compartments that are separated into 3 zones

Question 8

3 compartments of the tear film

Answer 8

lipid layer
aqueous layer
mucin layer

Question 9

lipid layer of the tear film

Answer 9

prevents the evaporation of tears

creates a seal to prevent spillover of tears at the lid margin

prevents skin lipids, bacteria, and other skin debris from moving onto the ocular surface

Question 10

aqueous layer of the tear film

Answer 10

provides immunological protection of the eye

anti adhesive and lubricant properties

thickest layer

Question 11

mucin layer of the tear film

Answer 11

interacts with the glycocalyx to facilitate the adhesions of the aqueous layer to the corneal surface through carbohydrate infections

maintain stability of tear film on the surface of the cornea

act as a viscoelastic buffer against mechanical shock by condensing to absorb pressure and expanding to release pressure

Question 12

what happens when there isn’t enough tear film

Answer 12

deficiency in any of the layers can lead to poor protection of the ocular surface

Question 13

how to treat a deficient lipid layer?

Answer 13

it can vet rated through dietary modification {increased omega-3 fatty acid intake} as well as warm compresses to relieve clogged meibomian glands

Question 14

how to treat a deficient mucin layer?

Answer 14

through the application of mucomimetic substances in order to facilitate bonding of the aqueous layer to the corneal epithelium

Question 15

what is the lipid layer of the tears composed of?

Answer 15

it is made of a mixture of lipids that are released with each eye blink
- melting point is 32 which ensures that it is a liquid on the ocular surface

Question 16

the primary lipid types found in the lipid layer

Answer 16

Primarily: 
wax esters 
diesters 
sterol esters
phospholipids 

less in amounts:
triglycerides
free fatty acids
free cholesterol

Question 17

wax esters

Answer 17

formed by long chain fatty acids linked by an ester bond with a long- chain alcohol

makes them amphiphatic, but mostly non-polar

Question 18

diesters

Answer 18

contain a hydroxy fatty acid which is linked via an ester bond to a fatty acid, and with another fatty acid or another alcohol ,

making them amphiphatic, but mostly non-polar

Question 19

sterol esters

Answer 19

formed when the hydroxyl group of cholesterol forms an ester bind with a long chain fatty acid

making them amphiphatic, but mostly non-polar

Question 20

phospholipids

Answer 20

contain 2 fatty acids and a phosphate group attached by ester bonds to a glycerol backbone, making them

amphiphatic, but more polar due to the present of the oxygen which is capable of hydrogen bonding

Question 21

the polar groups of the tear film

Answer 21

the polar lipids spread out over the tear film with the hydrophilic heads aligned towards the aqueous phase and the hydrophobic tails aligned towards the lid phase

Question 22

the non-polar groups of the tear film

Answer 22

take a more central position in the lipid layer,

this serves to increase the thickness of the layer

Question 23

the aqueous layer of the tear film composition

Answer 23

this is a dilute solution containing proteins and electrolytes

Question 24

major electrolytes of the aqueous layer

Answer 24

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

NOTE: levels of K+ are very high in tears

Ca2+ are very low in tears

Question 25

major proteins found in the aqueous layer

Answer 25

immunoglobulins {IgA, IgM,IgG)
lactoferrin
lipocalin
lysozyme

Question 26

immunoglobulins

Answer 26

all bind to foreign substances in oder to initiate an immunological response

Question 27

lactoferrin

Answer 27

iron- sequestering protein which acts as scavenger of free - radicals, as well as to inhibit the growth of iron- dependent bacteria

Question 28

lipocalin

Answer 28

globular protein that acts as a transport protein for retinoic acid and /or hydrophobic components of the tear film

Question 29

retinoid acid

Answer 29

derived from vitamin A

Question 30

lysozyme

Answer 30

is an enzyme found in the aqueous layer that destroyed certain gram- positive bacteria