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

Interpreting the Interactions

Now, if we ask: What is the actual distribution of contrast sensitivity in people who have visual acuity loss? Here you can see a normal contrast sensitivity is about 1.3. That’s the lower limit of normal. You get above 1.3, we won’t get too concerned about, but below 1.3 or lower. People in the 20/20, 20/60 range, the average contrast sensitivity is in the range of 1.2 and you can see contrast sensitivity just declines with each of the acuity tabs (slide 45). That’s just a restatement of what we saw before.

However, within these groups, there is a distribution (slide 46). There are people who have in this range – 20/20 and 20/60 – that have contrast sensitivity that is in the pits. They can’t see anything; everything is just totally washed out, even though they have relatively good acuity. And acuity, by the way, is measured with the highest possible contrast you can get. On the visual acuity chart are close to 100 percent contrast. And you can see there are a lot of people – about 40 percent of the people in the range between 20/20 and 20/60 have contrast sensitivity that would be considered moderately impaired.

Those of you who do illumination engineering probably know that as you go to higher spatial frequencies in the images, contrast falls. People who do remote sensing and that type of thing tell us that there’s almost a linear relationship between the contrast in terms of power versus the spatial frequency level. So the more detail there is, the bark on the tree will show more contrast than the tree; what gets lost is the detailed information, the pattern, the herringbone. The things that you designers are paid so much to put into the environment – they can’t see it, so you’re wasting somebody’s money.

And again, if you ask about contrast sensitivity – whether the contrast sensitivity tests out to be in the normal range, or they all say of course, they all came to a low vision clinic, so we kind of expect them to (slide 47). But then there are – it’s kind of a combination of an appearance.

The third thing that occurs is glare (slide 48). And what we find – and most of the glare [does not] come from eye disease in the retina, [but from] the cataract that didn’t get taken out, because if you have low vision, finding a cataract surgeon to take out that cataract can be pretty difficult, because they’ve been burned a few times where they’ve taken out the cataract and the vision hasn’t changed, because the person had a macular degeneration or something and they’re very unhappy. So you become a poor candidate [for cataract surgery], in technical terms, if you have low vision. And so a lot of the glare is coming from the cataract.