Related Experiment Video
Updated: Jun 11, 2026
Phenol Red Thread-based Sampling Procedure for Untargeted Tear Fluid Lipidomics in Biomarker Discovery
Published on: December 12, 2025
Measurement of phenol red thread tear test in Arabian and throughbred horses
Nihat Sindak1, Levent Kandemir, Muğdat Yertürk
1Department of Surgery, Faculty of Veterinary Medicine, Harran University, 63300 Sanliurfa, Turkey. nihats@harran.edu.tr
Objective:
To determine physiologic levels of tear production in Arabian (AH) and throughbred horses (TH) by using phenol red thread test (PRT).
Animals Studied:
The study was performed on 16 AH and 14 TH, ranging from 2.5 to 24 years of age, housed in a stable situated in the Sanliurfa of Turkey.
Procedures:
For the measurement of PRT, the strip was placed under the lower eyelid approximately one-third the distance from the temporal to nasal canthus and left for 15 s. The length of the wet area was measured in mm and compared among breed, sex, and age groups and between eyes of both sides.
Results:
The mean length of the wet area was in AH and TH were 30.22 +/- 0.99 mm ranging from 16 to 41 and 31.00 +/- 1.4 mm ranging from 14 to 47, respectively. There were no significant differences in tear production among breed, sex, or age groups. The values measured for left eyes were significantly higher than those for right eyes (P < 0.05).
Conclusions:
Phenol red thread test measurement is easily used, with no pain, and a comfortable method. PRT can be used in equine ophthalmology on a routine basis to the measurement of tear production. These normal PRT values help diagnosis keratoconjunctivitis sicca in horses.
