Normally a visual approach is the completion of an instrument approach by visual means. So there cannot be a general minimum for visual approaches. It always depends on the Instrument Part which brought you there.
PANS-ATM would disagree with you. A visual approach can replace an instrument approach in its entirety:
Visual approach. An approach by an IFR flight when either
part or all of an instrument approach procedure is not
completed and the approach is executed in visual reference
to terrain.
It gives no minimum visibility, simply saying:
6.5.3.3 An IFR flight may be cleared to execute a visual
approach provided the pilot can maintain visual reference to
the terrain and:
a) the reported ceiling is at or above the approved initial
approach level for the aircraft so cleared; or
b) the pilot reports at the initial approach level or at any
time during the instrument approach procedure that the
meteorological conditions are such that with
reasonable assurance a visual approach and landing
can be completed.
As previously quoted, JAR-OPS1 does specify a minimum:
(g) Visual Approach. An operator shall not use
an RVR of less than 800 m for a visual approach.