Environmental relative humidity affects Schirmer tear test results in normal dogs.

Abstract

OBJECTIVE: To investigate the effects of environmental temperature and relative humidity on tear test results in dogs. ANIMALS STUDIED: 22 normal dogs. PROCEDURES: Routine Schirmer tear tests (STT1) and phenol red thread tests (PRTT) were administered to normal dogs in four environmental conditions with different relative humidity (RH) and temperature (T). Environmental conditions (mean&#xa0;&#xb1;&#xa0;SD) included the following: normal indoor (RH&#xa0;=&#xa0;49&#xa0;&#xb1;&#xa0;4%, T&#xa0;=&#xa0;72&#xa0;&#xb1;&#xa0;2&#xb0;F), outdoor (RH&#xa0;=&#xa0;62&#xa0;&#xb1;&#xa0;11%, T&#xa0;=&#xa0;85&#xa0;&#xb1;&#xa0;6&#xb0;F), indoor high humidity (RH&#xa0;=&#xa0;85&#xa0;&#xb1;&#xa0;6%, T&#xa0;=&#xa0;71&#xa0;&#xb1;&#xa0;1&#xb0;F), and indoor low humidity (RH&#xa0;=&#xa0;39&#xa0;&#xb1;&#xa0;2%, T&#xa0;=&#xa0;76&#xa0;&#xb1;&#xa0;1&#xb0;F). ANCOVA models were used to assess for significant associations between tear test readings and RH/T (P&#xa0;<&#xa0;.05). RESULTS: A significant, direct positive relationship between RH and STT1 results was detected (y&#xa0;=&#xa0;0.04909*X&#xa0;+&#xa0;19.11, P&#xa0;=&#xa0;.006) but not between T and STT1. There was no significant relationship between PRTT and RH or T. CONCLUSIONS: These results suggest that STT1 but not PRTT is affected by RH and that T does not influence STT1 or PRTT results in normal dogs. RH is unlikely, however, to cause clinically significant effects on STT1 readings in normal dogs when performed in average indoor conditions. Future studies should investigate the influence of RH on STT1 readings obtained in dogs with keratoconjunctivitis sicca.