Evaluation 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’s length folded within the inferior cul-de-sac and the remaining 25 mm projecting over the lower eyelid. The test can be performed with the patient’s eyes open or closed, but some recommend that 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. See Chapter 3 for a discussion of ATD.
The Schirmer I test, which is similar to the basic secretion test but is done without topical anesthetic, measures both basic and reflex tearing. Less than 5.5 mm of wetting after 5 minutes is diagnostic of ATD. Although this test is relatively specific, its sensitivity is poor. Using lower thresholds increases the specificity of the test but decreases its sensitivity. The Schirmer II test, which measures reflex secretion, is performed in a similar manner but with topical anesthetic. However, after the filter-paper strips have been inserted into the inferior fornices, a cotton-tipped applicator is used to irritate the nasal mucosa. Wetting of less than 15 mm after 2 minutes is consistent with a defect in reflex secretion. Although an isolated abnormal result for any of these tests can be misleading, serially consistent results are highly suggestive of ATD. Schirmer testing is also useful in demonstrating to patients the presence of ATD. An alternative to use of the classic Schirmer strips involves use of a cotton thread impregnated with phenol red, which allows for quicker assessment of tear secretion but has not been fully validated.
Greiner MA, Faulkner WJ, Vislisel JM, Varley GA, Goins KM. Corneal diagnostic techniques. In: Mannis MJ, Holland EJ, eds. Cornea. Vol. 1. 4th ed. Philadelphia: Elsevier; 2017:116–122.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.