Juxtacanalicular connective tissue or basement membrane in Schlemm's canal site of outflow resistance

Aqueous outflow resistance seen in the eyes of patients with glaucoma most likely is generated either in theextracellular matrix of the juxtacanalicular connective tissue or the basement membrane of Schlemm's canal, saidMark Johnson, PhD, of the Department of Biomedical Engineering, Northwestern University, Evanston, IL.

Over and above this process, the location of giant vacuoles and pores seen in the cells of the endothelium inSchlemm's canal are likely responsible for modulating this outflow resistance, which is inversely proportionalto the number of pores. The mechanical stresses that are generated when the aqueous moves through theendothelium are likely responsible for the formation of the giant vacuoles and pores, Dr. Johnson explained.

An issue that needs further study is in vitro perfusion of the inner wall endothelium. This factor, according toDr. Johnson, may provide insight into the process by which vacuoles and pores form in this unique endotheliumand why inner wall pore density appears to be reduced greatly in patients with glaucoma.

Dr. Johnson and his colleagues proposed that funneling-movement of the aqueous into the nearestpore-causes the fluid to go through only a small part of the juxtacanalicular connective tissue orbasement membrane.

"This hypodynamic interaction greatly increases the flow resistance of the system," he said. "The flowresistance of the juxtacanalicular connective tissue plus the pores is much greater than the flow resistance ofeither of the two alone."

Other research issues that need to be addressed are creation of a cell culture model of the inner wall systemthat can study basal to apical perfusion, the basal lamina, and attachment to the juxtacanalicular connectivetissue; the biophysics of pore formation; determination of the permeability of juxtacanalicular connectivetissue and the basal lamina; determination of which extracellular micromolecules are responsible for generatingthe bulk of outflow resistance; and measurement of the pressure decrease across the inner wall in glaucomatouseyes, Dr. Johnson said.