Several microscopic variables are analyzed in the GDLS such as&colon; porosity, tortuosity and permeability. However, several ways to adapt methods estimating tortuosity in 2-D have also been tried. More extensive models account for paper tortuosity, pore radius, and paper deformation. Radial nerve fiber layer (NFL) without NFL tortuosity. Fractal dimension has been used to quantify tortuosity. However, the tortuosity of the rock increases this to a higher number than 1. However, it is well known that tortuosity is not only a function of porosity. This would imply that roughness (or tortuosity) could be measured by relative change of curvature. However, in this case tortuosity of a straight line is left undefined. In this case tortuosity of both straight line and circle is estimated to be 0. Tortuosity has been used in ecology to describe the movement paths of animals. Tortuosity is a property of a curve being tortuous (twisted; having many turns). In pharmaceutical sciences, tortuosity is used in relation to diffusion-controlled release from solid dosage forms.