title: Diurnal variations in tear film break-up time determined in healthy subjects by software-assisted interpretation of tear film video recordings.
abstract: BACKGROUND
  This study was designed to examine diurnal variations in tear film break-up time (BUT) and maximum blink interval (MBI) and to assess two different ways of calculating these variables on video recordings of the BUT test interpreted with the help of especially designed software. The repeatability of interpreting BUT video recordings was also addressed.
  
  
  METHODS
  Twenty-six healthy young adults were enrolled after ruling out dry eye according to a battery of tests (ocular surface disease index, McMonnies questionnaire, Schirmer test, phenol red test and corneal staining). BUT and maximum blink interval were determined on video-recordings of the BUT test conducted over a day in four sessions (9.30 am, 12.30 pm, 3.30 pm and 6.30 pm). In each session, the test was repeated three times to give three videos in which three BUT and MBI values were obtained by a masked observer. BUT and MBI were determined by averaging the three measurements and by averaging only the two closest measurements. Finally, two further experienced observers re-examined the videos to assess the repeatability of the BUT measurements made.
  
  
  RESULTS
  No diurnal variation in BUT was observed regardless of whether three or two video measurements were averaged. Significant correlation was detected between BUT and MBI. Inter-observer repeatability was better when BUT times were no longer than 15 seconds.
  
  
  CONCLUSIONS
  Tear film BUT was not influenced by the time of day and moderate to strong correlation with MBI was observed in all four sessions. The software-assisted method proved useful and identified the need to clarify the BUT end-point and to limit the test to 15 seconds to improve observer repeatability.
authors.affiliation: Departamento de Física Aplicada (Grupo de Optometría), Universidade de Santiago de Compostela, Santiago de Compostela, Spain. hugo.pena@usc.es.
authors.forename: Hugo
authors.initials: H
authors.lastname: Pena-Verdeal
authors.affiliation: Departamento de Física Aplicada (Grupo de Optometría), Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: García-Resúa
authors.affiliation: Departamento de Ciencias de la Computación (Grupo VARPA), Universidade de A Coruña, A Coruña, Spain.
authors.forename: Lucía
authors.initials: L
authors.lastname: Ramos
authors.affiliation: Departamento de Física Aplicada (Grupo de Optometría), Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Yebra-Pimentel
authors.affiliation: Departamento de Física Aplicada (Grupo de Optometría), Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
authors.forename: Ma Jesús
authors.initials: MJ
authors.lastname: Giráldez
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D015590:Fluorophotometry; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D012984:Software; D013666:Tears / Q000502:physiology*; D014741:Video Recording; D055815:Young Adult
keywords: diurnal variations; maximum blink interval; tear break-up time; tear film