Mechanical Properties of the Iris Dilator and Stroma Using Nanoindentation

In certain disorders of the eye such as angle-closure glaucoma [1], pigment dispersion syndrome [2], and intra-operative floppy iris syndrome [3] the contour of the iris plays an important role. The active iris contour is determined by a combination of external stresses arising from the flow of the aqueous humor and internal stresses due to the passive and active components of the constituent tissues. For example, in angle closure, the iris bows anteriorly, and the abnormal shape and position of the iris are directly related to the blockage of aqueous humor outflow, increasing the intraocular pressure. While the interaction between the aqueous humor and iris has been studied [4], little is known about the effect of the components of the iris on the contour. The iris is composed of stroma, pigment epithelial cells, and two constituent muscles, the sphincter iridis and dilator pupillae (Fig1).