Thanks a lot for you answer. What we have, that's only requirements, definitions and yours (I mean - world wide) professional experience. As ICAO docs state:
"Cat I and II ILS procedures differ from those of Cat IIIa in one important
respect. They require that the crew visually spot the approach lights — and, eventually, other runway environment cues — in order to safely continue to a
landing by visual reference alone. In other words, the landing pilot must be able to properly judge the flare point, make the landing, and execute the rollout visually.
Cat IIIa approaches, on the other hand, merely require that the pilot establish sufficient visual reference with the touchdown zone lights to
ensure that landing is occurring in the touchdown zone. The pilot may never even see the approach lights. Visual reference may be such that the pilot is unable to properly judge the flare point or manually control the aircraft during the initial rollout. The autopilot will normally execute the flare, landing, and rollout down to taxi speed."
Of course, I mean the only CATIIIA real visual conditions. It's clear, if you land in good weather you can make the decision - to land or to go around.