Which tear test uses a small thread that changes color to indicate tear production over 15 seconds?

Which tear test uses a small thread that changes color to indicate tear production over 15 seconds?

• A. Schirmer 1
• B. Schirmer 2
• C. Phenol red thread test
• D. Fluorescein dye test

Answer: (C)

Measuring tear production quickly relies on a test that uses a thread treated with a color indicator. The phenol red thread test uses a small thread soaked with phenol red; when placed in the lower eyelid for about 15 seconds, tears change the color along the thread from yellow to red. The length of the red portion corresponds to how much tear production occurred in that short interval. This makes it a rapid, straightforward way to quantify tear production in a clinical setting. Other tests work differently. Schirmer tests use filter paper strips placed under the eyelid for several minutes to measure how much tears wet the strip, based on wetting length rather than a color change. Fluorescein dye testing involves instilling dye and observing tear film stability and corneal surface staining, not measuring tear production over a short period.

Measuring tear production quickly relies on a test that uses a thread treated with a color indicator. The phenol red thread test uses a small thread soaked with phenol red; when placed in the lower eyelid for about 15 seconds, tears change the color along the thread from yellow to red. The length of the red portion corresponds to how much tear production occurred in that short interval. This makes it a rapid, straightforward way to quantify tear production in a clinical setting.

Other tests work differently. Schirmer tests use filter paper strips placed under the eyelid for several minutes to measure how much tears wet the strip, based on wetting length rather than a color change. Fluorescein dye testing involves instilling dye and observing tear film stability and corneal surface staining, not measuring tear production over a short period.