An impaired ability to respond to dark conditions suggests Vitamin A deficiency. This article outlines result of a study conducted in Zambia, in which researchers tested consumption of biofortified orange maize alongside white maize, then tested for symptoms of night-blindness or impaired vision. The study suggests that biofortification may be an effective way to prevent these deficiencies.
Palmer, C. et. al. The Journal of Nutrition (October 2016). Vol. 10. No. 146.