Optics: Tear Film Optics

Question 1

Epithelium

Answer 1

Protects the cornea by providing a barrier against water, larger molecules, and toxic substances

Question 2

Bowman’s membrane

Answer 2

Consists mainly of randomly arranged collagen fibrils

Question 3

Stroma

Answer 3

Comprises 90% of corneal thickness and over 200 collagen lamellae

Question 4

Collagen fibrils within each lamella run _______ to each other and the successive lamellae run _________

Answer 4

Parallel, across the cornea at angles to each other

Question 5

Desemet’s membrane

Answer 5

The basement membrane of the endothelial cells

Question 6

Endothelium,

Answer 6

Single layer that regulates the fluid balance of the cornea in order to maintain the stroma at about 78% hydration

Question 7

Dua’s layer

Answer 7

Located between the stroma and descemet’s membrane, comprised of type-1 collagen bundles

Question 8

Pre-corneal tear film is the…

Answer 8

Most anterior refractive surface of the eye

Question 9

Tear film is composed of _______, ___________, and ________ layers

Answer 9

Oily, aqueous, mucous

Question 10

Refractive index of tear film

Answer 10

1.336

Question 11

Optical power of the tear film

Answer 11

48.35D

Question 12

Tear film is essential for…

Answer 12

Clear vision and reduces transparency when the tear film dries out

Question 13

Stability of tear film is important for the…

Answer 13

Optical quality of the eye

Question 14

The chief function of the tear film lipid bilayer is to:

Answer 14

-provide smooth optical surface for the cornea
-retard water evaporation from the ocular surface

Question 15

Tear film stability is measured by its..

Answer 15

Lack of stability

Question 16

Tear film refers primarily to ….

Answer 16

Evaporation rate

Question 17

A stable tear film is one in which a…

Answer 17

Minimum amount of tears evaporate

Question 18

Instability of the tear film occurs due to the…

Answer 18

Depletion of aqueous component of tears

Question 19

Tear film optics is very significant because…

Answer 19

The change in the refractive index at the air-tear film interface is greater than any other interface in the eye

Question 20

Due to the large change in refractive index in the air-tear film interface, irregularities in the anterior surface of the tears have potential to…

Answer 20

Significantly degrade the optical quality of the eye

Question 21

Qualitative assessment of the tear film is realized by using:

Answer 21

-retro-illumination of pupil with slit lamp
-fluorescein

Question 22

Dry eye is a disorder of the tear film due to…

Answer 22

Tear deficiency or excessive tear evaporation which causes damage to the interpalpebral ocular surface and causes ocular discomfort

Question 23

High order aberrations are _____ times greater in dry eyes than in healthy eyes

Answer 23

2.5

Question 24

Contact lenses sit….

Answer 24

In and not on the tear film

Question 25

The contact lens is about _______ times thicker than the aqueous layer in the tear film

Answer 25

10

Question 26

Contact lens interaction with the tear film is dependent on the:

Answer 26

-lens material
-individuals tear chemistry

Question 27

Effects of contact lens wear on the tear film:

Answer 27

-deplete the levels of specific components in the tear film by sorption
-lens can stimulate the biochemical generation of additional components

Question 28

Factors affecting tear film stability:

Answer 28

-stability decreases significantly w age
-men have longer tear film breakup time (TBUT)
-Caucasian’s have higher TBUT
-generally affected by presence of contact lens
-ocular surgery
-local irregularities
-external environmental conditions
-smoking and alcohol intake
-amount of computer exposure