Hydrogen ion concentration of human tears: Effects of prolonged eye closure.

Using a closed chamber microelectrode technique, human tear hydrogen ion concentration was measured following periods of eye closure of 6 to 8 hours and then compared with normal open eye findings from the same patients. Closed eye tears were found to be significantly more acid (average age difference = 26 nM/1) and required some 3 to 4 hours to return to average open eye levels. The population rate for this return averaged 6.9 nM/1/hr. This degree of acid shift measured for prolonged eye closure, however, remained, for the average patient, well within comfort limits commonly cited, and appeared insufficient to distrub the water content or optical parameters of hydrophilic polymers in common use today for therapeutic or cosmetic purposes.