Week 1 - Tear Film & its Relation to Cls Flashcards
What are the 3 layers of the tear film? (Inner to outer)
Mucin layer (inner mucus)
Aqueous layer (watery middle)
Lipid layer (outer oily)
What is the basic function of the mucin layer?
adheres tear to the eye
What is the basic function of the aqueous layer?
nourishes and protects the cornea
What is the basic function of the lipid (oil) layer?
lubricates and prevents evaporation
Why do we assess the conditions of the tear film? 3
-help determine good cls candidates
-slightly dry eyes negatively impact cls
-aid with selection of appropriate lens design.
Dry eye is also known as ………………
Keratoconjunctivitis sicca
What are the 10 symptoms of dry eye?
- Soreness
- Tiredness
- Grittiness
- Dryness
- Burning
- Itching
- Photosensitivity
- Foreign body sensation
- Irritation
- Discomfort lid heaviness
What is tear osmoloarity?
a measurement used to determine how much salt is in your tears
What is hyperosmolarity?
tears have too much salt in them
If someone has hyperosmolarity, what can it indicate?
that tears are evaporating too quickly leading to aqueous deficiency
What test is done to detect tear osmoloarity?
TearLab
How is the TearLab test conducted?
The test device is
touched to the tear lake
in the outer corner of the
eye with the patient
looking up
A value greater than 300
mOsm/L is considered
abnormal. T/F
True
What does TBUT stand for?
Tear Break Up Time
What does TBUT measure?
measures the stability of the tear film to assess for evaporative DED.
How does the TBUT test work?
measures the time between the last blink and the first dry spot in the tear film
Less than 10 seconds in the TBUT is abnormal. T/F
True
What two things do we use when measuring the TBUT? 2
Fluorescein + cobalt blue illumination
What are we measuring when considering tear quantity or tear volume?
the amount of tears the patient has
The tear prism height is measured using the biomicroscope. T/F
True
What height is considered normal when measuring tear prism?
0.20mm - 0.40mm
What measurement during the tear prism test does it suggest reduced tear volume?
less than 0.20mm
What measurement during the tear break up test is suggests poor drainage?
more than 0.40 mm
How does the Schirmer’s test work? 2 steps
-the thick strip of filter paper is placed in both inferior fornices for 5 minutes
-strip is removed and the amount of tear is measured in millimeters
What is oxygen transmissibility?
measurement provided by the lab for the movement of oxygen in cls material
Oxygen transmissibility is measured in Dk/t.
What does high Dk/t value indicate?
there is more oxygen movement in a lens
Oxygen transmissibility is measured in Dk/t.
What does a low Dk/t value indicate?
there is less oxygen movement in a lens
In hydrogel contact lenses, the higher
the oxygen transmissibility in a
material the higher the water content.
This does not ring true for Silicone
Hydrogels though.
What can we change in the contact lenses to suit someone with dry eyes? 4
-change to a soft highly lubricious lens
-change to a lens that displays minimal eye- dehydration
-replace lenses more frequently
-refit to RGP
