The number of people suffering from glaucoma exceeded 400,000 in 2009, almost double 2002’s 210,000.

Aging seems to be the most common cause of the disease that can eventually lead to blindness, the National Health Insurance Corporation said Monday.

Glaucoma is a complicated disease in which damage to the optic nerve leads to progressive, irreversible vision loss. It is the second most common cause of blindness, according to the Glaucoma Foundation.

The largest demographic with the disease was men in their 80s, followed by those in their 70s and 60s. For women, those in their 70s took the highest number followed by those in their 60s and 80s. The increase in the disease was more evident among females as the growth rate was 1.9 times higher than for males.

“Doctors haven’t found a way to recover the damaged nerves in the eyes yet. The only way to prevent vision loss is to visit doctors regularly for checkup and screening. One cannot feel any symptoms before he or she is about to lose their vision,” Dr. Park Jong-un of Ilsan Hospital said.