RetiredF4:
The reported visibility to allow the beginning of a circling approach and to get a clearance for it was measured RVR. To fly the approach we used inflight visibility and airport environment in sight.
RVR controls only for a runway, it does not a substitute for prevailing visibility. So, under U.S. rules, commercial ops cannot begin a CTL unless the prevailing visibility is not less than the visibility minimum shown on the chart for your category of CTL. Typically, that would be 2 s.m. for Appch Cat D. Now, if the prevailing visibility is indeed 2 s.m. (or greater) but RVR is being reported for the runway to which you intend to circle, you have a problem. (RVR is not reported in the U.S. greater than 6,000.)
BTW, RVR in the U.S. is not visibility, it represents the "sighting conditions" (FAA's term, not mine) you can expect to have upon touchdown in the TDZ.