What does the phenol red thread test actually measure?

Alan Tomlinson, Kenny J. Blades, Edward Pearce

Research output: Contribution to journalArticlepeer-review

91 Citations (Scopus)


This study attempts to resolve whether the phenol red thread test (PRT) is a test of tear volume or tear production through comparisons with other techniques. Twenty asymptomatic subjects (10 men and 10 women; average age 30.6 +/- 10.8 years) had PRT (Zone Quick, Menicon) results compared with tear turnover rate (by fluorophotometry; Fluorotron Master, OcuMetrics) and tear volumes (from tear meniscus height and back extrapolation from fluorometric data). PRT wetting was not correlated with either tear turnover or volume (by fluorophotometry or tear meniscus height) on a Pearson product moment correlation test (p > 0.05). No clear experimental evidence in favor of the PRT being a measure of tear production or volume was found. It is probable that the PRT measures uptake of a (small) amount of fluid residing in the eye, stimulates a low degree of reflex tearing, and reflects the absorption characteristics of the thread dependent on the biophysics or composition of tears.

Original languageEnglish
Pages (from-to)142-146
Number of pages5
JournalOptometry and Vision Science
Issue number3
Publication statusPublished - 1 Mar 2001


  • vision sciences
  • tear production
  • phenol red thread test (PRT)


Dive into the research topics of 'What does the phenol red thread test actually measure?'. Together they form a unique fingerprint.

Cite this