March is National Save Your Vision Month. An important cause of blindness for people 60 and over is glaucoma, which has been predicted to impact close to 3.3 million people in the U.S. by next year, 2020. Early detection and treatment are crucial to prevent this “sneak thief of sight.”

Glaucoma is a disease of the optic nerve in the eyes, in which the pressure in the eye is too high for the optic nerve. This pressure causes progressive damage. There are chronic and acute forms of glaucoma, though the vast majority of people have the chronic version. In this form, the optic nerve damage is insidious and symptom-free. Much less common is an acute attack of glaucoma, which is associated with a dramatic rise in eye pressure and brings people to medical attention due to pain and acute visual loss. As a result of its being a mostly quiet disease, most people who have glaucoma do not even know it, and the diagnosis is usually made in the setting of an eye doctor’s office.

So, what does glaucoma actually cause? It is a disease that tends to affect the peripheral vision in its early stages, and initially causes only subtle changes in the visual field. Unchecked, this visual field loss will progress, and the classic hallmark of advanced glaucoma is tunnel vision, in which a person may be seeing 20/20, but only through a small window of central vision. Even with that damage, however, people may sometimes be unaware of this field loss, since it has occurred slowly enough over time to allow the brain to adapt. Optic nerve damage can also occasionally cause central vision loss early on, a rarer symptom, though one that does bring people sooner to medical attention.

Currently, 2.2 million people in the U.S. have glaucoma. Given the potential devastation to one’s vision that can be wrought by glaucoma, why isn’t everyone routinely checked for it? The 2005 findings of the U.S. Preventive Services Task Force (USPSTF) looked at population-based screening for glaucoma. The study found “insufficient evidence to determine the extent to which screening . . . would reduce impairment in vision-related function or quality of life.”  The study’s conclusion also cited the potential harms of early treatment, including cataracts, and summarized its findings in saying that the USPSTF “could not determine the balance between the benefits and harms of screening for glaucoma.”

Since this study, however, multiple professional groups, including the American Academy of Ophthalmology, have addressed the issue of screening for glaucoma. While almost all agree that widespread population screens are not effective, it is useful and productive to target those at risk for glaucoma. All agree that those at risk include people over the age of 60; people with a family history of glaucoma; and African Americans, who are especially at risk as they get older. Other risk factors that most agree on are extreme nearsightedness; prior history of eye trauma; diabetes; and Hispanic background, especially over the age of 65.

The reasons for focused, risk factor–based glaucoma screenings are many. We know that glaucoma is generally asymptomatic, and that very few people report to a doctor with actual complaints related to glaucoma. We know that early treatment delays or prevents the progression of the disease, and preserves vision by slowing the worsening of visual field defects. From even a purely economic standpoint, diagnosing glaucoma early pays for itself. By preserving visual function in older people, and by maintaining people’s’ ability to continue unassisted in their activities of daily living, glaucoma diagnosis and treatment decreases the disease’s overall burden to society.

Glaucoma screening is, in itself, a multifactorial process, and one that requires a skilled eye professional. It involves measuring intraocular pressures, assessing optic nerve head damage, and performing visual field testing. While measuring intraocular pressure tends to be the traditional barometer, it is actually not very sensitive in picking up glaucoma after all. Intraocular pressures tend to vary quite widely, and up to the number 21 can be considered “normal.”  However, many people with glaucoma never actually have elevated eye pressures, so a so-called normal pressure reading alone does not protect you. In fact, despite evidence of optic nerve damage, only 1 in 10 to 15 people actually has high eye pressures at screening.

A second element in the screen is the optic nerve head assessment. This can be done visually through a dilated pupil, in which the eye doctor uses a lens to assess nerve appearance, and inspects for evidence of damage. There are also automated nerve analysis machines, which digitally map the optic nerve and surrounding nerve fiber layer. This technology is useful in conjunction with an optic nerve exam; in and of itself it tends to be less diagnostic, because of intra-observer variation and measurement artifacts.

Lastly, there is the automated visual field exam. This exam, when done correctly, can pick up visual field defects well before any confrontational (finger wiggling) field exams could. However, these exams do tend to be a bit long, and can be subject to multiple testing errors and difficulties, including a test-taker’s lack of focus, sleepiness, distraction, and other issues. Newer types of visual field machines, like those employing frequency-doubling technology, are much faster and tend to have a higher predictive value. This technology will likely eventually replace traditional fields, at least for screening purposes.

Despite the USPSTF’s study findings, the Centers for Medicare and Medicaid Services does support, since 2002, annual glaucoma screening for those at high risk. Again, these groups include African Americans (over the age of 50, per CMS protocol); Hispanic Americans (over the age of 65); people of any age with a family history; and diabetics. The agency also recommends an initial screen of African Americans, or those of African descent, to be performed at ages 20 to 29. People aged 40 to 64 are recommended to be checked for glaucoma every 2 to 4 years, and those over 65 should be checked every 1 to 2 years.  Other than Medicare, several organizations do offer free glaucoma screens. These include Eye Care America, The Lions Clubs, Vision USA, and Friends of the Congressional Glaucoma Caucus Foundation.  If you feel that you are at risk for glaucoma, these organizations may be helpful in providing at least an initial assessment.

The good news is that if found and treated early, glaucoma progression can usually be halted or slowed, thus preserving vision for many years.

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