title: Fluorophotometric measurement of pH of human tears in vivo.
abstract: OBJECTIVE
  To measure the pH in the precorneal tear film of humans in vivo using a pH-sensitive fluorescent dye, bis-carboxyethyl-carboxyfluorescein (BCECF).
  
  
  METHODS
  The measurement was initiated by instilling 1 microliter of 2 mM BCECF solution into the subject's eye. The pH was calculated by measuring the ratio of fluorescent intensities at two excitation wavelengths (490/430 ratio), which was dependent on pH, but independent of the dye concentration and other variables. The tears of the same subject were then collected and loaded on to a micro pH-meter to ensure the accuracy of the measurement.
  
  
  RESULTS
  The mean pH values of 40 eyes from 20 healthy volunteers was 7.50 (SD +/- 0.23), which corresponded well with those measured by the micro pH-meter.
  
  
  CONCLUSIONS
  The method described was useful in measuring the pH of the precorneal tear film of humans with minimal invasion.
authors.affiliation: Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yamada
authors.forename: H
authors.initials: H
authors.lastname: Mochizuki
authors.forename: M
authors.initials: M
authors.lastname: Kawai
authors.forename: M
authors.initials: M
authors.lastname: Yoshino
authors.forename: Y
authors.initials: Y
authors.lastname: Mashima
mesh_terms: D002138:Calibration; D005452:Fluoresceins; D005456:Fluorescent Dyes; D015590:Fluorophotometry; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D013666:Tears / Q000378:metabolism*
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D006859:Hydrogen; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein