A June 2021 study by the Universidad Complutense de Madrid (UCM) and the ICTAN (Institute of Food and Nutrition Science and Technology) of the CSIC said,
"Although this was the baseline hypothesis, we did not see any effect either on adaptation to darkness or on visual acuity measured in low light conditions (mesopic vision), either with cocoa or with berries,"
"We need to conduct certain further studies as proof of concept to confirm that the effect is real and that the results could be applied to the design of products which could help to improve visual acuity and attention in defined populations,"