Measurement of tear secretion in healthy pigeons by using the phenol red thread test

The objectives of this study were to determine the applicability of the phenol red thread (PRT) test as a new method for the evaluation of tear secretion in healthy male and female pigeons, to establish normal physiologic reference values in these animals, and to compare seasonal variations in these values. Seventy-five pigeons of both sexes, with no ocular abnormalities, were included in the study. The phenol red impregnated thread was inserted into the recessus conjunctiva inferior for measuring tear secretion. After 15 seconds, the thread was removed and the wet portion of the thread was measured (in mm). The mean±sd PRT values were 23.02±2.98 mm/15 seconds and 24.04±2.60 mm/15 seconds for the April and June measurements, respectively. There were significant differences in the PRT between the two months, with a significant increase in June. Mean PRT values for males and females were, respectively, 23.30±3.35 and 22.79±2.65 mm/15 seconds in April, and 24.57±2.41 and 23.61±2.68 mm/15 seconds in June. There was no significant correlation (r=0.075, P>0.05) between bodyweight and tear production in both eyes of the male and female birds in April and June. The results indicated that seasonal variations have an effect on tear production. The PRT was a viable method for the measurement of tear production in pigeons and these measurements could be accepted as reference values for healthy pigeons.