Tear Film

Question 1

What are the purposes of the tear film?

Answer 1

Acts as a smooth refracting surface and lubricant between cornea and lid, and is the primary source of oxygen to the cornea

Question 2

What are the three layers of the tear film?

Answer 2

Mucin, aqueous, lipid

Question 3

True or false: Mucin binds physically with glycocalyx

Answer 3

True.

Question 4

What (besides water) composes the aqueous layer?

Answer 4

Electrolytes and antibacterial proteins

Question 5

What is the function of the aqueous layer?

Answer 5

To provide oxygen to the cornea

Question 6

What (besides lipid) composes the lipid layer?

Answer 6

Cholesterol

Question 7

What are three methods of tear-film evaluation?

Answer 7

Schirmer test (length of time to wet a strip of filter paper); red thread test (phenol-soaked thread measures tears); TBUT.

Question 8

What percentage of the tear film drains from the eye?

Answer 8

75% (the other 25% evaporates)

Question 9

List the pathway of tear drainage.

Answer 9

Pool in lacrimal lake –> lacrimal punctum –> lacrimal canaliculli –> lacrimal sac –> nasolacrimal duct (through valve of Hasner) –> inferior nasal meatus

Question 10

What does the Doane theory of tear movement state?

Answer 10

Lid closure compresses the canaliculli and sac, moves tears into the duct

Question 11

What does the Jones theory of tear movement state?

Answer 11

Lacrimal sac expands, causing negative pressure, which pulls tears into the sac with lid closure

Question 12

True or false: the potassium component of the tear film is 5-7x greater than in serum.

Answer 12

True.

Question 13

Which immunoglobulin is most common in a healthy tear film?

Answer 13

IgA

Question 14

Which mucin genes are expressed in the ocular surface?

Answer 14

MUC1, 2, 4, 5AC, 7, 13, 15, 16, and 17