Human tear PH.

To the Editor .—The article "Human Tear pH" by Carney and Hill in the MayArchives(94:821-824, 1976) concludes, among other things, that tears are more acid in the morning, taken from a yet unopened eye (average pH, 7.25) than later in the day (pH, 7.45; P Another explanation may be that the loss of carbon dioxide (CO 2 ) in the open eye alcalizes the tear fluid. Hind and Goyan 1 showed that in an open system, the pH rose about 0.3 pH units in the course of one minute. In calves' eyes, Pedersen 2 found a tear pH of 7.44 ± 0.007 using microcapillary glass electrodes. However, corrected for CO 2 (40 mm Hg), the pH was 7.29 ± 0.003. When I estimated