“…14 In addition to pressure gradients, these fluid movements may generate shear stress at the nerve head. Whether these vitreal forces are bad, good, or irrelevant for the nerve is impossible to say, but we can say that they likely gradually decrease with age (see below) and become small once presbyopia becomes complete, again at about the age when POAG begins to appear 47,48. And, of course, any of the effects may not be on the nerve directly but rather on the astrocytes and other glial elements associated with the nerve head and the lamina 49.…”