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.