The quantity of tears that are produced by the eye is measured by a test named Schirmer Test. In this test filter paper strip is used to measure the amount of tears that are produced over a period of 5 minutes.The strip is placed at the junction of the middle and lateral thirds of the lower eye lid. The test is done under ambient light.
The patient is instructed to look forward and to blink normally during the course of the test. A negative test which is more than 10 mm wetting of the filter paper in 5 minutes means you produce normal quantity of tears. Patients with dry eyes have wetting values of less than 5 mm in 5 minutes.
Tear Film Break up Time (BUT) is also used most commonly for testing dry eye. Blinking maintains the tear film continuity. If you keep your eyes open long enough, without blinking, the tear film will start breaking up. A strip of fluorescein is applied in the lower eyelid fornix and then removed.
The patient is asked to blink three times and then look straight forward, without blinking. The tear film is observed under cobalt-blue filtered light of the slitlamp microscope and the time that elapsed between the last blink and appearance of the first break in the tear film is recorded with a stopwatch. A break is seen as a dark spot in a sea of blue. Fluorescein BUT of less than 10 seconds or less is consistent with dry eyes.