Formation of Intra-Ocular Fluid and Permeability of the Ciliary Body. ∗

Abstract

Previous investigations have shown that there is a continuous circulation of the intra-ocular fluid, the chief source being the ciliary body, the chief exit being the canal of Schlemm. 1 The ciliary body exhibits an irreciprocal permeability to water and to methylene blue, both of which pass readily from stroma to epithelium but not in the reverse direction. 2 The present study was directed toward the discovery of the physico-chemical factors involved in this irreciprocal permeability. We have found that the tissue is permeable in both directions to acid and neutral crystalloid dyes, but impermeable in both directions to non-reducible basic crystalloid dyes. The stroma is capable of reducing methylene blue while the epithelium is capable of oxidizing methylene white. The passage of methylene blue from stroma to epithelium occurs therefore in its reduced, neutral state. By using a series of oxidation-reduction indicators, we found that the difference in oxidation-reduction potential between the epithelium and the stroma amounts to 100 millivolts.

At a pH of 5.3–5.5 the charge on the membrane barrier between epithelium and stroma is reversed, at lower pH the membrane barrier is permeable to basic dyes, impermeable to acid dyes, at higher pH the reverse is true. The membrane, therefore, is negatively charged at normal pH. This conclusion was confirmed by the production of an artificial electro-endosmotic flow in the proper direction through the tissue by means of an externally applied E.M.F.

In order that there should be a unidirectional flow of water by electro-endosmosis through a charged membrane there must be an electron conductor in the system. It is possible that a reversible oxidation-reduction system within the membrane could act as such an electron conductor. If the charge on the membrane is reversibly altered by the addition of oxidants or reductants at a fixed pH, the membrane must contain a reversible oxidation-reduction system.