  // get the eye pose and projection matricies once
  if (!this->LeftEyePose)
    {
    this->LeftEyePose = vtkMatrix4x4::New();
    this->RightEyePose = vtkMatrix4x4::New();
    this->LeftEyeProjection = vtkMatrix4x4::New();
    this->RightEyeProjection = vtkMatrix4x4::New();
    }
