For a CatI landing the visual requirements are quite vague in that you must only see any part of the approach/runway edge/centrelines lights. If passing 1100' on the approach or FAF and despite the iRVRs reading 400m, the pilot has full CatI visual requirements and the runway is in full and continuous sight then is it admissible to land?
afaik basicly yes. when you have positive visual contact with the runway or approach lights you may continue to decision altitude. at decision altitude always the crew makes final decision if to land or not regardless of the reported RVR .
if you cannot see anything and the weather is reported below minimums you are not allowed to approach until DA.
of course at extreme low RVR reports you should be extreme careful even when you see the runway from far away since you may like described run into extreme shallow fog on flare , loose orientation and get into severe problems when you nearly made it.