A silent disorder is rising among older people worldwide, as millions unknowingly grapple with glaucoma – an eye condition that can cause irreversible blindness but shows no obvious symptoms until late-stage disease, ophthalmologists warn.

It’s predicted that by 2050, the number of people with glaucoma will surge by more than 200%, highlighting an urgent need for heightened awareness, early detection, and advanced treatment strategies. “That’s a lot of people with a blinding disease who don’t know they have it,” said Joel S. Schuman, MD, a professor of ophthalmology and co-director of the Glaucoma Service at Wills Eye Hospital in Philadelphia. “Late in the disease, people may notice they’re tripping over the curb, or walking into things they didn’t see. It really is only in very advanced diseases that people notice there’s anything wrong.”

Glaucoma is the second leading cause of blindness worldwide, affecting 3 million people in the United States, and yet half of those affected are unaware, according to the CDC. Recent research at the University of Gothenburg in Sweden underscores glaucoma’s stealthy nature: 5% of 560 70-year-olds had the disease, and half of those did not know they had it before they took part in the study. “Living with glaucoma, especially without realizing it, can be very isolating,” said Lena Havstam Johansson, a PhD student at the University of Gothenburg and a specialist nurse at Sahlgrenska University Hospital, who did the study. “It may lead people to stay at home to avoid trouble.”

Once symptoms arise, some may notice patchy blind spots in their peripheral vision, and in their central vision in late stages. While many people assume they are getting clumsier with age, Schuman said, they often have a condition that can be slowed with the right treatment. Glaucoma occurs when there is increased pressure within the eye, causing damage to the optic nerve, which transmits information from the eye to the brain. If left untreated, it will result in partial vision loss or complete blindness. It often develops gradually and without noticeable symptoms in its early stages, earning it the nickname “the silent thief of sight.”

Though there are various types of the disease, about nine in 10 people in the U.S. have primary open-angle glaucoma (POAG). It is most common among people over the age of 60, those with a family history of glaucoma, and people who have diabetes. It disproportionately affects Black people, who are six times more likely than White people to have advanced vision loss from the disease.