Section 8.5.1.2 in the IEC 60601-1 has this sentence: "Opto-couplers complying with IEC 60747-5-5:2007, or a later edition, are considered equivalent to the requirements of 8.8.2 and 8.9.3."
Section 8.8.2 deals with reinforced insulation. In this case, reinforced insulation translates to 2xMOPP.