• The Stokes-Einstein equation and the physiological effects of vitreous surgery [editorial]

      Stefansson, Einar; Loftsson, Thorsteinn (Blackwell, 2006-12-01)
      Removal of the vitreous humour influences the physiology of the eye. The diffusion characteristics of small molecules in the vitreous cavity are changed dramatically by the removal of vitreous gel and its replacement by aqueous humour. This effect is predicted by the Stokes−Einstein equation (Sinko 2006). In vitrectomy the vitreous gel is replaced by water. As vitreous humour is 99% water, the chemical change is not terribly great, but there is an enormous change in viscosity. All liquids possess a definitive resistance to flow; viscosity is a measure of internal flow friction or the resistance of liquid molecules. The higher the magnitude of viscosity, the more resistant the liquid will be to flow. The viscosity of water is 1.00 centipoise (cp) at 20 °, whereas that of vitreous gel is 300–2000 cp (Lee et al. 1992; Soman & Banerjee 2003). The change in viscosity has a major effect on diffusion and thereby on the transport of all substances through the vitreous cavity. The amount (M) of compound flowing through a unit cross-section (S) of a flow barrier in unit time (t) is known as the flux (J):