"Diabetes is a leading cause of poor eyesight and blindness worldwide. Because the changes are painless and gradual, people often only realize they have a problem when their eyesight finally begins to fail," said Ban in a message to the World Diabetes Day which falls on Monday.
Ban said it's vital for people with diabetes to have regular examination so that they can get advice and timely treatment to prevent things getting worse.
World Diabetes Day, which is held annually on Nov. 14, is the primary global awareness campaign focusing on diabetes mellitus.
UN statistics show that some 422 million people now live with diabetes. Its prevalence has nearly doubled in the past 35 years, with the increase greatest in low- and middle-income countries.
The disease shortens lives and, if not managed, can cause severe complications such as amputations, strokes or kidney failure.