title: Comparison of the tear film clinical parameters at two different times of the day.
abstract: OBJECTIVE
  The aim of the present study was to analyse the quality and quantity of the tear film in a young, healthy and non-contact lens-wearing population with measurements taken in the morning and in the afternoon to establish if changes exist in these parameters.
  
  
  METHODS
  In a controlled laboratory setting, morning and afternoon clinical parameters of tear film were assessed. Schirmer test, tear meniscus height, break-up time and non-invasive break-up time were measured in 51 normal subjects on the same day for each individual.
  
  
  RESULTS
  Tear volume showed no significant changes during the day but tear film stability was significantly reduced at the end of the day (p < 0.001), demonstrating that tear film stability is affected by the time of day.
  
  
  CONCLUSIONS
  Researchers and clinicians might wish to consider these differences when comparisons are made between studies and populations and also when the same patient is observed over periods. Fluorescein instillation can affect the measurements of tear stability in subjects with poor quality tear film.
authors: Centre of Physics (Optometry), School of Sciences, University of Minho, Portugal. mlira@fisica.uminho.pt
authors: Madalena
authors: M
authors: Lira
authors: M Elisabete C D Real
authors: ME
authors: Oliveira
authors: Sandra
authors: S
authors: Franco
mesh_terms: D004334:Drug Administration Schedule; D015352:Dry Eye Syndromes / Q000188:drug therapy / Q000378:metabolism*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D012016:Reference Values; D013500:Surface Tension; D013666:Tears / Q000737:chemistry*; D055815:Young Adult
chemical_list: D009883:Ophthalmic Solutions