Chapter 9 325 Several parameters were calculated to characterize an eyelash fiber assembly and included eyelash curvature, length, and volume or thickness.60 In order to perform measurements on eyelashes, we glued commercial eyelashes on a Teflon cylinder similar to the manner employed when they are placed on a person’s eyelid. We first take a digital photograph with a perspective similar to that of an observer when positioned in the same plane—90 degrees clockwise to the focus. As seen in Figure 12, untreated and mascara treated eyelashes result in a different geometric arrangement of the fibers. The ends of the lashes are in a higher position in the treated sample as compared to the untreated control. Likewise, mascara treatment results in an increase in the radius of curvature of the eyelashes. The %Curl of an eyelash can be measured from a digital image if we know the arc length (L) and radius (r) of the curl. %Curl = L - r L 100 Eq. 17 where r is the radius and is defined by: r = (x start - x end )2 + (y start - y end )2 Eq. 18 Using equations 17 and 18, the %Curl was calculated for two eyelash samples, similar to the ones shown in Figure 12, resulting in values of 23.09±2.22 and 32.09±1.42 for untreated and mascara treated samples, respectively. This correlates well with visual observations of the image in Figure 12. Please keep in mind, however, that treatment of the eyelash will depend on the person administering the treatment, mascara formulation, and accompanying mascara brush. In this study, treatment was administered with 10 brush strokes of the mascara, starting from the base of the lash and dragging the brush to the lash tips. In addition to the measurements already discussed, we can also measure the alignment, gluing together, and darkening of the