title: The tear (lacrimal) meniscus height in human eyes: a useful clinical measure or an unusable variable sign?
abstract: OBJECTIVE
  To review notes and reports in the literature on assessments of human tear meniscus height (TMH) with the view to defining what the current state of knowledge is, and allow comparisons with data obtained on elderly individuals.
  
  
  METHODS
  TMH data was obtained from 97 elderly individuals without significant eye disease. Photo-slit-lamp views, perpendicular to the lower marginal tear strip, were used to obtain close-up images by videography over approximately 30s. Repeated measures at the same location separated by a few seconds (time-dependent TMH measures, tTMH), or repeated measures along the length of the middle portion of the lower eyelid (position-dependent TMH measures, pTMH) were made. The results were compared to those from published reports of TMH.
  
  
  RESULTS
  For elderly individuals, tTMH averaged 0.185+/-0.088 mm, while pTMH averaged 0.189+/-0.093 mm. The distribution of TMH measures however included a number of data sets with a much higher average, and which could be separated from the main group of data using cluster analyses approach (> 0.23 mm, P < 0.001). Literature-reported values for TMH, assessed by a perpendicular view, average 0.215 mm (range of average values from 0.163 to 0.350 mm), whereas those made from a tangential view average 0.343 mm (range 0.215-0.460 mm).
  
  
  CONCLUSIONS
  The average TMH value of close to 0.2mm in the elderly, as compared to the small number of individuals with rather greater TMH values of up to 0.7 mm, might therefore be considered as indicative of their having normal tear volume, with a few individuals having reflex tearing. Based on the data and literature values, a lower cut-off limit for normal would be </=0.1 mm, while >/=0.25 mm would indicate reflex tearing and/or sub-optimal tear drainage. An alternative interpretation is that elderly individuals have a subnormal tear film volume, with just a few individuals having adequate tear volume. Further work is clearly needed to resolve this issue.
authors.affiliation: Department of Vision Sciences, Glasgow-Caledonian University, Glasgow G4 0BA, UK. m.doughty@gcal.ac.uk
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Doughty
authors.forename: Mohammad
authors.initials: M
authors.lastname: Laiquzzaman
authors.forename: Emil
authors.initials: E
authors.lastname: Oblak
authors.forename: Norman
authors.initials: N
authors.lastname: Button