What does a Schirmer tear test (STT) result of less than 15 mm/min indicate?

A Schirmer tear test (STT) result of less than 15 mm/min is indicative of aqueous deficiency. This test measures the production of tears, specifically the aqueous component, which is essential for maintaining a healthy ocular surface. When the test result falls below the threshold of 15 mm/min, it suggests that the tear production is insufficient to meet the needs of the eye, leading to dryness and potential damage to the corneal surface.

Aqueous deficiency can be a primary condition, such as in dry eye diseases like keratoconjunctivitis sicca, or secondary to other underlying health issues. The STT is a crucial diagnostic tool used to assess tear production and help veterinarians diagnose conditions related to inadequate tear film stability, which is often a predominant problem in various ocular disorders.

Other options, such as lipid deficiency, mucin deficiency, and viral infections, pertain to different aspects of tear film composition or unrelated ocular conditions. For instance, lipid deficiency relates to the oily layer of the tear film, mucin deficiency affects the mucin component stabilizing the tear film, and viral infections typically present with different clinical signs and are not directly assessed by the STT.