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

Reduced Visual Acuity

The major causes of functional limitations from low vision or reduce visual acuity (slide 27). And looking at the distributions of acuity in the sample (slide 28), about 35 percent of the people who present to a low-vision clinic have acuity in the range of 20/20 to 20/60. So these people feel their vision’s bad enough that they’re seeking services. Close to 40 percent are the range of 20/60 to 20/200. About 20 percent are 20/200 to 20/500 and about 6 percent are worse than that. Somewhere in the neighbor of about 26 percent are legally blind.

But if you ask these people how’s your vision rate on a scale of zero being poor to four being excellent, the average rating is between poor and fair – no matter what your visual acuity when you come in (slide 29). And you’ll notice even those with the range of 20/20 to 20/60 are included. To be fair, some of these people have glaucoma. Glaucoma can shrink your visual fields way down and not necessarily have to do with central vision. A lot of these people also have dry forms of macular degeneration, which can produce what’s called foveal sparing. The center can still read the eye chart, but it’s like looking through a keyhole. And surrounding that would be a blind area so that they could still have very poor vision, even though they might be able to read quite far down on the eye chart.

Question by [Participant]: Are those corrected numbers – the visual acuity?

Response by Bob Massof: I’m sure that they’re not coming in for refract records. So these are people who have best-corrected visual acuity on presentation. I should say they’re wearing their individual correction. If they needed correction, they don’t get into the database. Now, if they get corrected and back to normal, they’re happy. You’ve cured their low vision. Same with [those who] come in with a cataract and you say, you came into the wrong department. You have to go over here and get the cataract done. They don’t come back. They not in these databases. So these are people (slide 29) who stayed in the database.

Visual acuity is a measure of blur. My daughter’s gotten over it, but I haven’t. And that the – now, I’m just simulating 20/200 visual acuity (slide 30). So if the only thing that was occurring was blur, the picture on the left would [represent] 20/20, the picture on the right is what 20/200 would look like. That’s the difference. And you can overcome that blur with magnification (slide 31). And that’s the main trick that’s used in a low vision clinic: to provide people with telescopes and magnifiers to compensate for the loss of acuity. You can read the bigger letters on the charts and make everything bigger and you can make the compensation.