ATC must ensure that weather conditions at the airport are above certain minima (in the U.S., a ceiling of 1000 feet AGL or greater and visibility of at least 3 statute miles) before issuing the clearance. According to ICAO Doc. 4444, it is enough if the pilot reports that in his/her opinion the weather conditions allow a visual approach to be made. In general, the ATC gives the information about the weather but it's the pilot who makes a decision if the weather is suitable for landing. Once the pilot has accepted the clearance, he/she assumes responsibility for separation and wake turbulence avoidance and may navigate as necessary to complete the approach visually. According to ICAO Doc. 4444, ATC continues to provide separation between the aircraft making a visual approach and other arriving and departing aircraft. The pilot may get responsible for the separation with preceding aircraft in case he/she has the preceding aircraft in sight and is instructed so by ATC.