Glaucoma is becoming an increasing problem in the United States, partly because of the record number of baby boomers aging together.
It's estimated that right now, there are about 60 million people worldwide living with glaucoma, but half of them don't even know it yet.
Dr. Jason Yeh, an ophthalmologist with Texas Tech Physicians, says it's called the "silent thief" because vision loss closes in on you from the side first.
"The reason why you don't have symptoms is the disease affects the peripheral vision first and then it gradually begins to affect the central vision. Ultimately, it will lead to blindness, if it's untreated," says Dr. Yeh.
January is glaucoma awareness month, a good time to make it a new year's resolution to get your eyes checked this year, and every year if you're over 40.