This paper is a continuation of two recent publications on crack growth in viscoelastic media. It provides further theoretical results for large strains that enable prediction of crack opening displacement for comparison with experimental data in the region of the singularity. In order to achieve good agreement with experiment it was necessary to account for far-field viscoelasticity. Additionally, it is found that with large deformation throughout the singularity, the deformation consists of simple shearing and stretching normal to the crack plane. Thus, there is no significant displacement parallel to the crack plane; such simplicity exists for materials that stiffen or soften at high strains if the stress obeys a power law in strain at high strains. This finding means that, despite the frame-dependence of the theory, there is no local rotation in the singularity to affect the stress.