Villagers grind rocks to separate the gold, causing dust with lead to settle on soil and expose people to the poison.
The World Health Organization estimates that there are currently as many as 246 million people living with visual impairment worldwide and a further 39 million who are already completely blind. Of that number, 90 percent live in developing countries where there are fewer opportunities for prevention and cure.
The vast majority of forms of blindness are preventable.
The lead cause of blindness in the developing world is cataracts, which can be congenital (from birth), or caused by trauma to the eye later in life. The operation to remove cataracts is both simple and cheap.
A single eye surgeon can carry out thousands in a year, each one taking as little as 10 minutes.
Yet, in places like the east African island of Zanzibar, where there is not a single paediatric eye surgeon, and much of the population lacks the access or the funds to receive the vision-saving operation, many continue to suffer needlessly.
The NGO Sightsavers has been funding a team of surgeons and medical specialists from the Tanzanian mainland who visit four times a year to carry out mass child-cataract operations.
Two-year-old Bakir Rashid underwent the surgery in September 2016.