FLUOROPHOTOMETRIC MEASUREMENT OF PH OF HUMAN TEARS IN-VIVO

Purpose. To measure the pH in the precorneal tear film of humans in vi vo using a pH-sensitive fluorescent dye, bis-carboxyethyl-carboxyfluor escein (BCECF). Methods. The measurement was initiated by instilling 1 mu l of 2 mM BCECF solution into the subject's eye. The pH was calcul ated by measuring the ratio of fluorescent intensities at two excitati on wavelengths (490/430 ratio), which was dependent on pH, but indepen dent of the dye concentration and other variables. The tears of the sa me subject were then collected and loaded on to a micro pH-meter to en sure the accuracy of the measurement. Results. The mean pH values of 4 0 eyes from 20 healthy volunteers was 7.50 (SD +/- 0.23), which corres ponded well with those measured by the micro pH-meter.Conclusions. The method described was useful in measuring the pH of the precorneal tea r film of humans with minimal invasion.