Have a look in your Jeppesen/AIP at the runway approach lights and marking distances.
You will thence able to work out what your visibility is at the minima based on what airfield infrastructure you can see.
For instance there will be 5 cross bars spaced at 150m. It is 900m from the start of the HIAL to the green threshold lights.
On a standard cat 1 ILS at roughly 200 feet AGL (a typical ILS minima) on a 3 degree path, with 800m vis you will be above the 1st cross bar and should be able to see at least the other 4 cross bars and very shortly after the threshold lights.
You will certainly not be able to see the touchdown zone or papi at the minima with 800m vis.
Hope this helps.