Electrical conductivity of tear fluid in healthy persons and keratoconjunctivitis sicca patients measured by a flexible conductimetric sensor.

Abstract

It is known that the osmolarity of tears increases in keratoconjunctivitis sicca (KCS) patients and therefore could be a sensitive and specific indicator for the diagnosis of KCS. However, owing to the difficulties in using the current methods of tear fluid measurement these procedures have not been employed in clinical practice. A newly devised flexible conductimetric sensor fabricated using microelectronic techniques is small and flexible enough to be placed on the ocular surface to measure the electrical conductivity can be considered as an indirect function of electrolyte activity, or osmolarity. Therefore, we applied this new sensor to measure the tear fluid conductivity in KCS patients and healthy volunteers. A flexible conductimetric sensor, consisting of a hydrophilic polytetrafluoroethylene membrane placed between two gold-coated layers, was placed directly into the temporal conjunctival cul-de-sac. The tear fluid conductivity was monitored graphically on a computer display. The sodium chloride concentration of tear fluids was calculated from the calibration curve and converted to the equivalent electrolyte concentration. The electrolyte concentrations were 324.8 +/- 41.0 mEq/1 in KCS patients (29 samples obtained from 16 KCS patients) and 296.4 +/- 30.1 mEq/1 in healthy persons (33 samples obtained from 17 healthy persons). The difference was significant (P < 0.01). A positive correlation was found between the electrolyte concentrations in KCS and the rose bengal score (coefficient = 0.36). The tear fluid conductivity in healthy persons and KCS patients could be monitored without ocular damage, and the measured values were consistent with previous reports. This method will be a new diagnostic tool for detecting tear abnormalities.