Cause Found for Elevated Pressure in Glaucoma

Glaucoma, a leading cause of irreversible blindness, is associated with elevated pressure in the eye. This elevated pressure is essentially due to a plumbing problem. Fluid builds up in the eye, increasing pressure and eventually damaging the optic nerve. For nearly 150 years, researchers have been trying to understand what causes the blockage that prevents the eye from draining properly. In a unique study of human ocular cells, a multi-institution research team led by a biomedical engineer at Northwestern University has found a new culprit. Glaucoma appears to be a consequence of mechanical dysfunction of endothelial cells -- a thin layer of cells that is the final barrier to fluid entering Schlemm’s canal (image), from which fluid then drains from the eye. The researchers found that these endothelial cells from eyes with glaucoma are stiffer than cells from healthy eyes. This stiffness limits the cells’ ability to deform and allow a fluid called aqueous humor to cross the endothelium and drain into Schlemm’s canal. This increased flow resistance is responsible for the elevated pressure associated with glaucoma. The findings were published online on September 8, 2014 in PNAS. “There is (presently) no cure for glaucoma, which affects more than two million Americans,” said Dr. Mark Johnson, the senior author of the study. “Our work shows that cells of this endothelial layer act as mechanical gates. Therapeutic strategies that alter the stiffness of these cells potentially could lead to a cure for this debilitating disease.” Dr. Johnson is a professor of biomedical engineering and mechanical engineering at Northwestern’s McCormick School of Engineering and Applied Science and a professor of ophthalmology at Northwestern University Feinberg School of Medicine.