You can use Epoque, Sea and Sea, Olympus or Inon wide angle lens with PT010 housing. Basically the housing can take any 67mm thread external lens. Underwater, all of these lens will give you around 90-100 degree view, using on land (still need to have the camera in the housing though as you can't mount the lens directly on the camera), you can get around 130-140 degree view.
The port of the housing has pretty decent glass on it so it does not affect the quality too much. However depending on the situation, you can get quite a bit of distortion with these wide angle lens on land. Generally I recommend Inon mainly because there is an option to add Inon Dome port later so you can get about 130-140 degree view underwater as well, if you wish.