HYDROGEN ION CONCENTRATION OF TEAR FLUID

Various reports are available on investigations into the hydrogen ion concentration of the tear fluid. The results of these differ. Some writers claim to have seen a neutral reaction (pH about 7.0), or more often a slightly alkaline pH value, about that of serum (7.3 7.5), while others have noticed a still more alkaline reaction. Oguchi et al. found that the pH of the conjunctival fluid varies from 6.4 to 7.6 (most often 7.0 to 7.2). while admixture of tears gives a higher pH, and unmixed tears probably have a pH as high as over 8.0. Hosford et al. found the pH to be about 7.35. Felman, in 50 normal subjects, noticed tear pH values ranging from 5.2 to 8.35, the majority between 7.0 and 7.4. Gyorffy recorded pH values between 6.3 and 8.4, most often 7.2 7.5, in 150 contact lens wearers. Hind et al. found pH values ranging between 7.3 and 7.7 (average 7.47) in 7 7 normals. They reckoned, however, with a source of error towards the alkaline side and therefore judged the average pH to be more likely 7.40. Vidal found an average value of 7.3 (quoted by N . Ehlers). Pedersen-Bjergdrd et al., in 50 subjects, measured pH 7.3 7.5 (average 7.4). In a previous study, on the other hand, using a different technique, the pH of 10 subjects was stated to average 8.2.