Schirmer's test uses paper strips inserted under the eyelid for several minutes to measure the production of tears. The exact procedure may vary somewhat. Both eyes are tested at the same time. Most often, this test consists of placing a small strip of filter paper inside the lower eyelid (conjunctival sac). The eyes are closed for 5 minutes. The paper is then removed and the amount of moisture is measured. Sometimes a topical anesthetic in placed into the eye before the filter paper to prevent tearing due to the irritation from the paper. This technique measures basic tear function. Even though this test has been available for over a century, several clinical studies have shown that it does not properly identify a large group of patients with dry eyes. Newer and better tests of tear production and function are now emerging. One test measures an iron-binding molecule called lactoferrin. The amount of this molecule appears to be closely related to tear production. Patients with low tear production and dry eyes have low levels of this molecule. This test may be especially valuable for patients with dry eyes since it can point to specific treatment strategies for dry eye. The tears may also be examined for their content of lysozyme, an enzyme normally found in tears. Another test involves fluorescein eye drops, which contain a dye that is placed in the eye. The dye should drain with the tears through the lacrimal duct into the nose within 2 minutes. If patients do not have enough tears to flush the dye into the nose, this time will be longer. A new test is also available to more accurately measure the flow of dye out of the eye.
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