Proceedings of: Workshop on Improving Building Design for Persons with Low Vision

Prevalence and Incidence of Low Vision and Blindness in the U.S.

Okay, so how much is out there if we’re using these definitions of low vision? What’s the prevalence and incidence of low vision? Well, there have been a lot of numbers thrown around. I think it’s gone as high as about 20 million; it’s gone as low as 800,000, but it depends on what study you look at, how you go about counting it, how you define low vision.

There’s this Inhane Study which is done – you go around and ask people, basically, are you satisfied with your vision? And when you do that, you get a number that’s in the neighborhood of 17 or 18 million.

There have only been five studies published where they’ve actually gone out and measured people’s vision and then corrected their refractive errors and counted how many people in the community. One’s the Baltimore Eye Study; one’s the Beaver Dam Eye Study; one’s is the Framingham Eye Study; and the Salisbury Eye Evaluation Study and the Mud Creek Valley Study.

Age-related Data

I have a graph on this slide that shows the data from those five studies all plotted on the same graph (slide 14). And fit to the data is a curve that starts out kind of flat at ages around 55 to 60 and then accelerates and becomes very steep as you get passed age 75. And by the time you get to age 80, the prevalence rate is up about 10 percent. So saying that at around age 80, 10 percent of people will have visual acuity – in this case, worse than 20/70 in the better eye.

Okay, the Mud Creek Valley – all studies agree, except for the Mud Creek Valley study. The Mud Creek Valley study, the prevalence rates are much higher than the other studies. And the reason for that – Mud Creek Valley has, I think, one eye doctor for the entire county. And the cataract rate is at almost Third World levels in Mud Creek Valley, Kentucky. So that area was deliberately chosen to get some sense of what the prevalence of low vision and blindness were in different economic strata. Mud Creek Valley had the least amount of health care in all the areas we looked at so their numbers are bigger. So their numbers don’t fit the same curve. So if you’re trying to build a model based on a national average, the other studies would really give you a better picture.

But what this is saying is that the prevalence rate of low vision, as defined as 20/70 or worse for acuity and defining it the same way Medicare does, starts out around two-tenths of a percent of the population at age 55, accelerates to about 1 percent by the time you get to 70 and is up to 10 percent by the time you get to around 83 and it’s still going up.

So if you live long enough, you’ll get low vision and that’s one of the reasons why there is so much low vision today is that people are living longer, they’re outliving their eyes.

Now, the curve that fits the white population has a different shape from the curve that fits the black population. And the reason for that is the leading cause of low vision among Caucasians is age-related macular degeneration. The leading cause of low vision in the African-American population is glaucoma. And so glaucoma occurs a little earlier in life and it is – has a shallower rise. It doesn’t climb quite as rapidly as macular degeneration does.

Okay. From those curves, we also can estimate the incidents of low vision. And what we find here is the curves basically have the same shape (slide 15). You just take the curve over an exponential [derivative] and it’s saying that our annual incidents – by the time you get up to around 75 – you’re running at about a half-a-percent a year. And by the time you get up to past 80, you’re all the way up to 3 percent a year. So these are new cases of low vision each year. The prevalence is basically what is the census of low vision at any other point in time.

Projected Low Vision Prevalence over Time

Okay. This is just another graph showing the number of new cases per year, converting that incidents rate into actual numbers of people in the U.S (slide 16). Basically, what it’s showing is it’s down quite low in the order of 10,000 per year in the 55 to 59 years, by the time you get up to 85, it’s about 100,000 per year. For all people over age 65, it’s running between 200,000 to 250,000 new cases of low vision per year. Now, this was based on 2000 census data.

If we project from the 2000 census data using rates so we know change in actual incidents of preference rate, [we] find the incidents of low vision climb from about 210,000 in 1995 to over 500,000 by 2025 (slide 17). That’s because of the aging in the world population.

Question by [Participant]: Bob, is that an accumulative number or is that number –

Response by Bob Massof: New cases per year. It’s going to be 500,000 new cases per year.

Okay. If you’ll notice the prevalence figure – that’s almost a straight line relationship (slide 17). The prevalence increases – the prevalence in 1995 – and again, that’s 20/70 or worse, the Medicare definition – the prevalence increases from about 1.35 million in 1995 and it’s expected to – it’s a straight-line – climb up to about 2.4 million in 2025.

So why is the incidents climbing up kind of a power curve, but the prevalence is on a straight line? It’s because the cases of new vision [loss] are almost exactly balanced by the number of deaths in those age groups. And so the death rate almost matches. In fact, the difference is about 38,000 cases per year. And so – the growth. So prevalence can be misleading. If we’re looking at prevalence numbers, we’re underestimating the magnitude of the problem of the age of the population. New cases are coming in at about the same rate as existing cases are dying.

So based on the estimates for 2010, which I can safely make before the census results are out, vision in the range of less than 20/40 to greater-than or equal-to 20/60 in the better eye with best correction has a prevalence in the neighborhood of 2.5 million (slide 18).

Mild low vision, using Medicare’s definition – less than 20/60, but greater than 20/200 in the better eye with best correction – has a prevalence of about 750,000. And severe low vision, which is legal blindness, has a prevalence of about 1.25 million.

In the severe low vision group, the legally blind group, only 10 percent of that group have no useful vision. The rest have some degree of low vision. So the number of people who are totally blind runs in the neighborhood of about 120,000. They all belong to either the NFB or the ACB.

Comment by [Participant]: No, they don’t.

So the number that probably you should work with in terms of right now is something that’s in the neighborhood of about 4.5 million. Those are the numbers we’re using for our planning in terms of needs for service provision.

Question by [Participant]: I thought on the NEI website there were 30 million.

Response by Bob Massof: That’s how many people read the NEI website.

Response by Cheri Wiggs: More, now that I’ve posted up there.

As I said, there are numbers from all over the place. And depending on which study you quote and who you’re trying to impress, the criterion for how you [define] low vision will vary.

This is defined technically and this is defined for the purpose of who reads these technical definitions of low vision, not are you dissatisfied with your vision? And not that I’ve got visual impairment in one eye, but not the other eye. Macular degeneration doesn’t affect the two eyes equally. And so you could have 20/20 vision in one eye and 20/200 in the other eye. That person does not have low vision.

Comment by [Participant]: But that’s a matter of analysis. That’s a composite of all the studies.

Response by Bob Massof: Yeah.