[Measurement of pH, time-dependent-changes in pH, [Na+], and [K+] in human tears--comparison between normal subjects, subjects with decreased tear secretion, and contact lens wearers].

In order to investigate basic mechanisms of tear secretion and tear gland dysfunction, the pH, its time-dependent change (delta pH), [Na+], and [K+] of basal and reflex tears were measured. Subjects were humans with normal tear secretion or decreased tear secretion, and hard contact lens (HCL) wearers. Reflex tears were collected by administration of distilled water into the conjunctival sacs of the fellow eyes to study the secretory function of normal human lacrimal glands. In the clinical part of this study, reflex tears were collected from subjects before and after tasting horseradish paste. The [K+] and delta pH of the normal human reflex tears were significantly higher than in the basal tears according to the degree of stimulus until medium range. This suggests the presence of K(+)- and HCO(3-)-dependent secretory mechanism in the lacrimal glands. In the patients with decreased tear secretion, [K+] data of reflex tears were either higher than or equivalent to the data for basal tears. Therefore, the difference in amplitude of the stimulus-induced increase of tear [K+] suggests that there are two or more types of lacrimal gland dysfunction in patients with decreased tear secretion.