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

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.