A blocked tear duct is diagnosed based on a medical history, a physical exam, and other testing as needed.

Tests for children and adults may include:

• Fluorescein dye disappearance test. This is often used to determine whether tears are draining normally through the tear ducts from the eye into the nose.
• Culture and sensitivity test. This test helps determine whether infection is present. It may be done if mucus or pus is visible.

Additional tests are sometimes used, although usually only with adults. These tests may include:

• A Schirmer test, used to find out whether the tear glands are producing the normal amount of tears. Special small, soft paper strips are placed in the corner of the person's eyes for about 5 minutes to see how many tears are produced.
• A probe, which involves passing a thin metal wire through the blocked duct to determine where it is blocked. The area is numbed with a local anesthetic before the probe is inserted.
• Imaging tests, such as computed tomography (CT scan) or magnetic resonance imaging (MRI) of the head. Imaging tests may be done to locate the site and structural cause of the tear duct blockage.