7. Tear film assessment & dry eyes

Question 1

What is the role of the Muco- aqueous layer in the tear film? and what is it made of?

Answer 1

It is made of mucus and aqueous. Role: it contains different proteins & peptides.

Question 2

Role of the epithelium in the tear film?

Answer 2

Increase surface area, and it has finger-like projections that attach to the glycocalyx.

Question 3

4 functions of the tear film?

Answer 3

DOMN
1. Defense- Proteins and enzymes to kill microorganisms.
2. Optical- Provides a smooth optical surface by filling in small surface irregularities.
3. Mechanical- Wets and lubricates cornea and conj during blink
-Facilitates foreign body (FB) removal
4.Nutrients- Passage of oxygen and nutrients and waste removal

Question 4

What is pre-lens tear film and post-lens tear film?

Answer 4

Pre-lens tear film: found in front of contact lens
Post-lens Tear film: A small section of the tear film found behind the contact lens.

Question 5

What problem does contact lens cause to the tear film?

Answer 5

It creates 2 layers: Pre & Post lens tear film. These 2 layers are less table, leading to increased evaporation and increased osmolarity. These will additionally, increase inflammatory mediators and alerted composition of proteins and ions. Also, ocular surface temperature changes.

Question 6

Blinking is affected by?

Answer 6

Orbicularis oculi (7th cranial nerve)

Question 7

What causes blinking?

Answer 7

It is stimulated by the evaporation that causes the tear film to thin. Then cools the ocular surface. Thermo- receptive nerve fibres cause us to blink.

Question 8

Blinking has different functions in patients that wear CL, what are these 4 functions?

Answer 8

1. Tear spreading
2. Maintain clean free lens surface- minimise deposition
3. Removal of unwanted material
4. Facilitate tear exchange & mixing (To prevent post tear lens stagnation & Minimise hypoxia & hypercapnia- gaseous exchange enhanced by tear exchange).

Question 9

What are the 2 types of dry eyes? Which one is found more commonly in patients?

Answer 9

ADDE – aqueous deficient dry eye, describes conditions affecting lacrimal gland function

EDE – includes both lid-related (eg. MGD, blink related) and ocular surface-related causes (e.g. mucin or CL-related).

EDE is more common.

Question 10

Describe the vicious cycle of dry eyes

Answer 10

Due to excessive evaporation. The tear film is so concentrated for the cells. The epithelial cells on the ocular surface start releasing inflammatory mediators. Goblet cells start getting damaged. Damage to the epithelium is seen and it starts to apoptosis. As a result, tear film becomes less stable. Epithelium surface is damaged, goblet cells are lost.

Leading to tear film instability. Leading to more evaporation and tear film osmolality- CYCLE.