Essential spherical isometries

A result due to Williams, Stampfli and Fillmore shows that an essential isometry $T$ on a Hilbert space $\mathcal{H}$ is a compact perturbation of an isometry if and only if ind$(T)\le 0$. A recent result of S. Chavan yields an analogous characterization of essential spherical isometries $T=(T_1,\dots ,T_n)\in \mathcal{B}(\mathcal{H}{)}^n$ with dim(${\bigcap }_{i=1}^n\ker (T_i))\le$ dim$({\bigcap }_{i=1}^n\ker (T_i^{\ast }))$. In the present note we show that in dimension $n>1$ the result of Chavan holds without any condition on the dimensions of the joint kernels of $T$ and $T^{\ast }$.