Several tests are used to determine whether keratoconjunctivitis sicca (dry eye) is present:
- Schirmer test (tear secretion test): measurement of the amount of tear production; for this purpose, a 5-mm-wide and 35-mm-long filter paper strip (litmus paper) is inserted into the conjunctival sac at the outer corner of the eyelid and wetting is measured; after 5 minutes, the distance that the tear fluid has traveled in the paper strip is read) – to check the amount of tears [values ≤ 5 mm are certainly pathological/diseased].
- Examination of the composition of the tear fluid
- Assessment of corneal surface, eyelid position and lacrimal glands.
- Tear film break up time (TFBUT); also BUT after break-up time) – measure of tear film stability; for this purpose, the tear film is stained with fluorescein; then the tear film is observed through the slit lamp and the time is measured simultaneously. In this way, it is possible to see when the tear film breaks up. The normal time is between 20-30 seconds in a healthy eye. Sure pathological (pathological) are values below 10 seconds.
- Blink frequency (during speech (15 ± 13 blinks/minute) and reading (5 ± 4 blinks/minute) [typical for patients with dry eye are reduced intervals between blinks from about 6 seconds to 2.6 seconds].
Normal values for the tests (see above).
| Tests | Standard values |
| Schirmer test | > 5 mm |
| Tear film breakup time | 15/min |
| Blink rate | > 20 sec |
