Figure 2-7 Lissamine green staining of the conjunctiva. (Courtesy of Dasa Gangadhar, MD.)

Evaluation of the Tear Film and Tests of Tear Production

The basic secretion test is performed after instillation of a topical anesthetic and light blotting of residual fluid from the inferior fornix. To minimize irritation to the cornea during the test, a thin filter-paper strip (5 mm wide, 30 mm long) is placed at the junction of the middle and lateral thirds of the lower eyelid, with 5 mm of the paper folded within the inferior cul-de-sac and the remaining 25 mm of paper projecting over the lower eyelid. The test can be performed with the patient’s eyes open or closed, although some recommend the eyes be closed to eliminate blinking. Although normal tear secretion is quite variable, repeated measurements of less than 3 mm of wetting after 5 minutes, with anesthetic, are highly suggestive of aqueous tear deficiency (ATD), whereas 3–10 mm is equivocal.

The Schirmer I test, which is similar to the basic secretion test but is done without topical anesthetic, measures basic and reflex tearing combined. Less than 5.5 mm of wetting after 5 minutes is diagnostic of ATD. Although this test is relatively specific, its level of sensitivity is poor. Using lower cutoff measurements increases the specificity of these tests but decreases their sensitivity. The Schirmer II test, which measures reflex secretion, is performed in a similar manner but with topical