What clear to land said is correct.
ICAO annex 6 pt 1:
4.4.1.2 An instrument approach shall not be continued beyond the outer marker fix in case of precision approach, or below 300 m (1 000 ft) above the aerodrome in case of non-precision approach, unless the reported visibility or controlling RVR is above the specified minimum.
..."reported" is the key word. You cannot go down and have a look. Also, you should not even continue to destination unless the forecast RVR indicates you will at least get into your alternate. As per the same reference. And according to pt 2 the same applies to GA
Under EASA you may continue the approach but not below 1000' unless the RVR is above minimum.
[edit; with a nod to StudentInDebt who obviously types quicker than me]
[James Albright explains all this well on his site code7700]