The Swelling Pressure of the Corneal Stroma

¹ Department of Ophthalmology of the Massachusetts Eye and Ear Infirmary Boston, Mass. Paper 114, Retina Foundation.
² Department of Ophthalmology of the Massachusetts Eye and Ear Infirmary Boston, Mass. Paper 114, Retina Foundation.; Fight for Sight Research Fellow, National Council to Combat Blindness, Inc., New York, N. Y.
³ Department of Ophthalmology of the Massachusetts Eye and Ear Infirmary Boston, Mass. Paper 114, Retina Foundation.; E. B. Dunphy Fellow, Boston, Mass.

Various earlier methods to determine the swelling pressure of the corneal stroma are reviewed. Two recent methods are described in more detail: a rapid electronic method for determining the swelling pressure in vitro,⁴ and a method to determine the fluid pressure in the stroma of the living cornea.⁵ The stvelling pressure has been determined over a wide range of corneal hydration. At normal water content, the corneal stroma of the cow has a swelling pressure of 55 to 60 mm. Hg. Also, the influence of pH and ionic strength has been studied. If a fine cannida filled with saline and connected to a transducer manometer is inserted into the living cornea, a negative pressure is being built up. Tested on isolated tissue, the fluid pressure has the same numerical value as the swelling pressure. In the living rabbit fluid pressures of -40 to -50 mm. Hg have been found. The molecular basis of the swelling pressure is discussed. The swelling pressure energy is stored mainly in the stromal poly electrolytes, particularly the polysaccharides. Under normal circumstances, the stromal structure seems to be compressed between the epithelium and endothelium by the negative fluid pressure within the tissue which is probably maintained by an active transport across the cellular layers.