Glaucoma is a condition in which the optic nerve is subject to damage—usually, but not always, because of excessive pressure within the eye. If untreated, optic nerve damage results in progressive, permanent vision loss, starting with unnoticeable blind spots at the edge of the field of vision, progressing to tunnel vision, then to blindness.

More than two million people in the United States have glaucoma, 80,000 of whom are legally blind as a result. It is the leading cause of preventable blindness in the United States and the most frequent cause of blindness in African-Americans, who are at about a three-fold higher risk of glaucoma than the rest of the population. The risk of glaucoma increases dramatically with age, but it can strike any age group, even newborn infants and fetuses.

Glaucoma is actually a class of diseases—there are at least twenty different forms. It...