Infant’s dark-brown eyes suddenly turn indigo blue after COVID-19 antiviral treatment. But why?

The brown eyes of a 6-month-old boy turned a deep indigo blue after he was given the antiviral favipiravir to deal with COVID-19. 

This case is uncommon, but it surely’s not the primary time medical doctors have reported a affected person’s eyes altering coloration after they prescribed favipiravir for COVID-19. So what may very well be inflicting this weird impact?