Table 2. Assessment of risk of bias of the included studies.

Domain	Flaxel et al. 2012	Gomi et al. 2012	Russo et al. 2013	Wyględowska-Promieńska et al., 2014	Semeraro et al. 2015	Wyględowska-Promieńska et al. 2015
Random sequence generation	Low risk	Low risk	Low risk	High risk	Low risk	High risk
Allocation concealment	Unclear	Unclear	Unclear	High risk	Unclear	High risk
Blinding for visual acuity
Participants and personnel	High risk	Low risk	High risk	High risk	High risk	High risk
Outcome assessment	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
Blinding for other outcomes
Participants and personnel	High risk	Low risk	High risk	High risk	High risk	High risk
Outcome assessment	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
Incomplete outcome data	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
Selective reporting	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
Other bias	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk