The tear film provides several important functions for the eye, including polishing the corneal surface, trapping and flushing out debris, and reducing friction during eye movement. Several tests are used to evaluate the tear film and diagnose dry eye, including the BUT test, NIBUT test, Schirmer's test, fluorophotometry, phenol red thread test, Rose Bengal staining test, and tear osmolality test. Each test measures different aspects of the tear film and has defined normal and dry eye results.

1. Tear
Function
Tests

2. The liquid layer bathing the cornea and conjunctiva. It creates a perfectly smooth
liquid outer layer that polishes the corneal surface, mechanically traps and
flushes out foreign bodies and chemicals, contains bacteriostatic substances that
inhibit the growth of microorganisms, and reduces the surface friction associated
with eyelid blinking and eye movement.

3. •TESTS
1. BUT Test
2. NIBUT Test
3. Schimer Test
4. Flurophotometry
5. Phenol red thread Test
6. Rose Bengal Staining Test
7. Tear film osmolality Test

4. BUT Test (Tear Break Up Time)
How to perform
In testing for TBUT, sodium fluorescein dye is added to the eye and the tear film is
observed under the slit lamp while the patient avoids blinking until tiny dry spots develop.
▪ Fluorescein 0.5%
▪ Slit lamp magnification 10x
▪ Use cobalt filter
▪ Repeat three times & take
average

5. Test Results
> 10 sec – Normal
<10 sec – Dry Eye
< 5 sec – Sever Dry Eye

6. NIBUT Test(Non-invasive
tear Break UP Time)
How to Perform
A grid or concentric ring pattern is projected onto
cornea and patient is asked to blink. the rings will
appear distorted when cornea becomes dry. The
time interval between last blink and distorted ring
pattern gives the measurement of NIBUT.

7. • Conducted in quiet room with low air
speed and low general light
• Use techniques as keratometry,
modified keratometry & Tearscope
• Access Pre-corneal tear film ability
• A stopwatch was started after the
last complete blink.
Test Results
>15.4 +/- 2.4 sec – Normal
<15.4 +/- 2.4 sec – Dry eyes

8. Schirmer’s test
❑Rate of tear formation is estimated.
❑Whatman filter paper no 41 is used.
❑Dimension 5mm × 35mm.
❑5mm tab is folded at one end.
❑The bent end is placed at the junction of the
lateral 1/3rd and medial 2/3rd of the lower
conjunctival sac.
❑The test is performed in dim light with FANs and
ACS switched off.

10. Flurophotometry
Standardized amount of fluorescein is placed in conjunctival sac and tear
turn over rate is determined by persistent of fluorescein in tears at specific
timepoints later.
To detect amount of residual fluorescein is using schirmer strip to collect
fluorescein – stained tears.
Fluorophotometer : quantify amount of fluorescein persisting in eye
Minimally stimulated tear samples collected.
Using micro tube from inferior tear meniscus 15 minute after 5ul of 2%
fluorescein

13. Phenol red thread test
A sterile cotton thread is draped over the non-anesthetized lid
margin.
It changes color upon aqueous contact and the length of
colored thread is measured.
This test is used to evaluate the tear secretion quantity
without inducing significant reflex tearing.
The normative value is 13±4 mm of wetting over a fifteen
second period

14. Rose Bengal staining test
➢Rose Bengal solution 1% placed into
the conjunctival sac.
➢After a wait of 2 mins, degree of
rose bengal staining on bulbar
conjunctiva and cornea is quantitated
by microscopic exam.
➢Stains devitalized cells.
➢Also stains mucous strands (very
often present in KCS)

16. Tear film osmolality test
❑ Tear Samples are collected with hand-
drawn micro pippete from inferior
marginal tear strip, without disturbing
the ocular surface.
❑ Tear osmolality is determined by a
freezing point depression Osmometer.
❑ Normal – 295 to 309 mOsm / litre.
❑ Elevated in Dry Eyes.