STT stands for Schirmer Tear Test.

• A. Schirmer Tear Test
• B. Slit-lamp Tear Test
• C. Schirmer Threshold Test
• D. Sedimentation Tear Test

Answer: (A)

The main idea here is recognizing what STT stands for and what that test does. STT is the Schirmer Tear Test, a simple, widely used measure of tear production. It helps detect reduced tear flow, which is important for diagnosing keratoconjunctivitis sicca (dry eye) in dogs and cats.

In practice, a small filter paper strip is placed in the lower eyelid’s conjunctival sac for about 60 seconds. Tears wet the strip, and you read how many millimeters of the strip become moistened. The result reflects tear production: lower values suggest deficient tear production, while higher values can indicate normal or reflex tearing in response to irritation. Normal ranges are species-dependent but roughly fall in the mid-teens to mid-twenties millimeters per minute in dogs; values well below that raise concern for dry eye.

There are two common variants: one that measures total tear production (basal plus reflex tears) and another that, after topical anesthetic, aims to measure basal tear production by minimizing reflex tearing. The other listed terms aren’t used for this tear-volume measurement, so they don’t describe what STT actually assesses.