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

Keynote Address: Definition of Low Vision and its Impact on Accessibility and Performance

Robert Massof, Ph.D.: Professor, Lions Low Vision Research and Rehabilitation Center, Johns Hopkins School of Medicine

Henry Green: Our next presentation is by Professor Massof. But before he does, Vijay was nice enough to – Vijay, a number of years ago, was a great photographer. He went out and he really enjoyed photography and he’s got a number of photographs that’s he’s exhibited. And he gave us one out here during the Dogwood Festival in Washington, D.C. This is the Jefferson Memorial. We’ve got lots of them out there. So if you’d like them, just pick one up. And it’s kind of a little memento from the Workshop. So we appreciate it, Vijay.

Introduction and Definition of Terms

Thank you very much. Well, I want to thank Vijay for inviting me to participate – exciting and stimulating. I’ve been in the field long enough to have to explain what low vision is each time I get up and talk. It’s just great progress not to have to do that – to actually have a meeting organized for people outside the small circle of those that work on this problem all the time. To organize a meeting devoted to the subject says a lot about how important it’s become.

Vijay asked me to talk about – kind of introduce your client to you, to talk about the low-vision population, what the characteristics of low vision are, and how we define it. So that’s most of what I’m going to talk about. So my apologies to Dr. Alibhai, Dr. Siemsen and Dr. Brabyn who would probably do a better job giving this talk, but too bad.

Low Vision and Blindness

So let’s start with a definition of low vision. And I’ve heard a lot of definitions. Before I read what’s on the slide, low vision’s a medical term. And when ophthalmologists measure your vision, they measure visual acuity. And visual acuity is expressed as a ratio of 20/20, 20/200. So the larger the number in the denominator, the worse your vision is. And of course, the smaller the fraction – 20/20, is one; 20/200, point-one.

Operational Definitions

So if your vision is low, you have low vision acuity. So low vision is kind of a shorthand notation for low visual acuity. However, the use of the term “low vision” has gone well beyond just talking about visual acuity. In fact, it refers to any chronic visual impairments that cause functional limitations or disability (slide 3).

We say it’s chronic – by definition, it can’t be corrected with medical or surgical interventions. If you can take out the cataract, we don’t call it low vision; if we can give you glasses, we don’t call it low vision. We correct that. So low vision is after everything has been done that can be done and you’re still left with a bit of impairment that interferes with daily activities.

Visual impairment can refer to loss of visual acuity – I’ll explain what that is; loss of contrast sensitivity – I’ll explain what that is; loss of peripheral vision; blind spots and a number of other types of visual bursts, color vision deficiencies and so on, which – and usually, visual impairment is defined in terms of some type of clinical test that gives us a score that we can compare to norms and say whether or not there’s an impairment there. Some impairments cause more problems with daily functioning than other types of impairments and we’ll emphasize those that are most –have the biggest effect on daily functioning.

Functional limitations is a term that refers to an increased difficulty in being able to do certain functions that require vision. Reading is one of the functions we single out; mobility; visual motor activities – this is eye-hand coordination type things, using your hands under visual control; and interpreting visual information. You know, if you’re watching a reality TV show, in order to know what’s going on, you have to be able to interpret what you’re seeing. So an awful lot of what we do every day involves visual information processing and interpreting visual information.

So functional limitations usually imply that you have an increased difficulty doing it, but it’s not impossible to do. Whereas disability usually refers to the activities themselves that are impacted. So if you’re unable to perform your usual customary activities because of your visual impairment, we say you’re suffering a disability. And especially with the new [term] –– International Classification Function, disability has come to be defined strictly in terms of activities. So the two more or less go hand in hand, but you’re not necessarily disabled if you have a functional limitation.

Official Definitions

Okay, the official definition of low vision usually goes hand-in-hand with blindness, and low vision and blindness are often in the same sentence. And there’s a kind of commonsense definition of blindness. We think we have no useful vision, that you can’t use your vision at all. But then the technical definition of blindness is usually defined in terms of some level of visual impairment and it’s usually even visual acuity or visual fields.

The World Health Organization defines blindness as corrected visual acuity (slide 4). By corrected I mean wearing your glasses, getting the best vision you can. The corrected visual acuity that’s less than or equal to 20/400 in your better-seeing eye – and I’ll explain what these numbers mean – or your maximum diameter of your visual field is under 10 degrees. Then you qualify for the term blindness, according to the World Health Organization criteria.

World Health Organization finds low vision and its corrected visual acuity that’s less than 20/60, but it’s greater than or equal to 20/200. So if you’re in that range, your vision’s impaired, but still is useful to you, then use the term “low vision”. And they also include a visual field definition that if the maximum diameter of the visual field is 10 degrees or greater, but less than 20 degrees, then you earn the term low vision from the World Health Organization.

In the United States, blindness is defined as part of the Social Security Act for purposes of defining disability for disability benefits (slide 5). And blindness is – today is defined as corrected visual acuity in the better-seeing eye that is less than 20/100. It used to be less-than or equal to 20/200. The reason for the change is that we got new eye charts. The eye charts used to be 20/100, 20/200 was the next line. We got new eye charts and added a 20/160 line in between. Subsequently, we had a lot of people who could read 20/160; they lost their blindness-related benefits, because of 20/160.

So people like Dr. Siemsen and Dr. Alibhai had the old Snellen charts in the other room. And if you had to come in for a disability test, they’d take out the old Snellen chart and checked to see if – and finally, commonsense prevailed and said what you really mean is they can’t read the 20/100 line, they can read the 20/200. So the cut really is 20/100. So that’s the new definition of blindness for the disability insurance.

The maximum visual field [diameter of] less than 20 degrees. Remember, that’s the low-vision range for the World Health Organization; it’s blindness for the U.S.

Low vision is not a term that is used in that way; however, it is defined by Medicare. And to be eligible for payment for services that are provided for rehabilitation of your vision – receiving rehabilitation related to your visual impairment, Medicare defines low vision using ICD-9-CM codes – these are diagnostic codes (slide 5). And mild low vision, which they don’t pay for, is in the range of less than 20/40, but greater-than or equal to 20/60. Moderate low vision – they’ll pay for that – is less than 20/60 and greater than 20/200 and/or if your visual acuity is better-than or equal to 20/60, you have blind spots in your central field that interfere with your functioning. So if you can document that, you’re still classified as moderate, even though your acuity might not reach those particular [limits]. And severe low vision is anything less-than or equal to 20/200 – same definition as legal blindness.

The ICD-9-CM codes go onto to break up severe low vision into severe, profound, near-total blindness, total blindness, but in Medicare’s, those don’t make a difference. And so we’ve tended to just stop at the severe to be all inclusive after that.

Visual Acuity

So what is visual acuity? When we’re defining low vision on a basis of [Snellen] test, what is it we’re talking about? Well, visual acuity is just a measure of the limit of your vision resolution (slide 7).

And this is what is called the ETDRS chart (slides 7 and 8). It’s a new design of the eye chart. And if you visit any low-vision clinic or you participate in any type NEI-funded clinical trial, you’re probably familiar with this chart. Okay, 20/20 visual acuity means that the smallest letter that a person can identify is five arc minutes – and I know there are [engineers] in this room, so you know what that means and I’ll explain for those who aren’t (slide 9).

Five arc minutes of visual angle and size and has a critical detail of one arc minute. Okay, if you drop a triangle from the eye to the letters – so the letters at the base of the triangle point to the triangle at the eye. That angle at the eye is what we’re talking about – the size of the angle.

There are 360 degrees in a circle; there are 60 minutes in a degree. So one minute is pretty small. If stars are separated by one minute apart, you can see them as two stars, if you have 20/20 vision acuity. So this is the definition of limited resolution. If they’re closer together than one minute apart, it looks like one star. They blur together.

Okay. The absolute limit to visual acuity, if the optics of the eye were perfect, would be about 20-over-eight. And that corresponds to the distance between pixels in your retina. Okay, these are the photoreceptors. They’re sort of like – think of those like pixels in your camera. We used to say [film] in your camera. But nobody knows what we’re talking about. So each photo receptor we thought of as a pixel. So the limited resolution induced by the pixelized nature of the retina is about – would give you about 20-over-eight, whereas 20/20 is a more practical definition of normal vision as the optics of our eye are anything but perfect (slide 9).

Now, conventionally, we specify visual acuity as the minimum angle of resolution, which abbreviated is M-A-R – MAR (slide 10). And it’s the ratio of the distance to the letters on the chart divided by the size of the letters. And when we’re talking about Snellen notation, which is the 20/20, it is the Snellen notation that dates back to the 1800s (slide 11). He was a Dutch ophthalmologist who invented the eye chart and visual acuity measurements.

The standardized distance is 20 feet. Those of you who develop offices know that nobody has a 20-foot exam room, but we still specify the distance, as if we’re testing at 20 feet. Sometimes people who are purists will use mirrors to optically get the 20 feet, but for the most part, 20 feet is just an idea. So you measure the distance.

Twenty, the bottom number, the other 20, that’s the size of the letter. And the size is specified also as a distance. And it’s the distance at which that letter [transcends] five minutes of arc. So if it’s a bigger letter, you have to put farther away in order for it to be five minutes. So 20/20 says you can resolve this 5-minute arc letter at 20 feet and the size of the letter is five minutes of arc at 20 feet. Twenty-two-hundred means the letter is five minutes of arc at 200 feet, which means it’s 10 times bigger (slide 12). So, if 20/20 the smallest detail you can resolve is one minute of arc, in 20/200 the smallest detail you could resolve is 10 minutes of arc, okay? One-sixth of a degree. That’s pretty good vision, but you’re legally blind if that’s the best you can do. There are a lot of animals that would die to have 20/200 vision.

Okay, and the reason we have some problem with a small amount of visual acuity loss – small, relatively speaking – is because our whole society is built around normal vision. Newspapers, magazines are printed with print size that’s only three times the resolution limit of the average person – 20/20. It’s the size of 20/60 so it can be read comfortably. For most people who would have 20/40 acuity, they would struggle with 20/60, because it’s like trying to read the – if you have 20/20 vision – trying to read the back of the [one dollar] bill because the print size is too small.

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.

Characteristics of Low Vision Patients

Okay. So what are the characteristics of this low-vision population? In order to find this out, we had a network put together, a collaborative network of low-vision centers throughout the country (slide 20). There are 28 of these centers or 30 of these centers that are pooling from the patients they’ve seen. And about 60 percent of the centers are associated with academic medical centers. The other 40 percent are parts of group practices or private practices. So all of these low-vision specialists are combining their data together into a single database and this is an ongoing project. So what I’m giving you is a snapshot based on close to 1,000 patients that have been selected by this network. And it’s just sequential – it’s a series of patients.

So there’s obviously a selection bias, because obviously, patients have to be willing to join. So it shouldn’t be treated as an epidemiological study, but this will give you a good picture of the kinds of people who are seeking services in low-vision clinics.

Age and Gender

Okay. With all due respect to the youngsters in this room who have low vision, most people with low vision are old. The median age is 75 [- 76] years (slides 21 and 22). So half the people with low vision are older than that.

And here is the – this is just a histogram showing the distribution of number of patients in the sample who – by age who are presenting to these low-vision clinics (slide 22). And it’s heavily skewed to the older age – it’s a long tail that goes off to age 18 being the lowest age, and the median, as mentioned, being 76. The mean is 72 – standard deviation is about 16.

So for the most part, 80 percent of the people with low vision who are visiting low-vision clinics – and it agrees with the epidemiologic studies as well – are over age 65. Most people with low vision are women – two-thirds of them are women (slides 23 and 24). Why? Women live longer. See what you have to look forward to, ladies?

Okay. The age distribution of low vision among women is very similar to the age distribution among men – except there are just more women out there. The percentages – the distribution percentages are the same.

Visual System Disorders

Most people who have low vision have a central vision loss (slide 25). And this is a pie chart showing the various diagnoses of patients who come into these clinics seeking low-vision services (slide 26). 

Macular Disease

More than half – the ones that have some shade of yellow – are due to a macular disease. That’s a disease of your central vision, which is your acuity. Around 10 percent have glaucoma coming in seeking services. Diabetic retinopathy, which represents somewhere in the neighborhood of around 10-12 percent of the retinal vascular diseases is included in here. And stroke is about 2 percent. So by far, most of the people who are seeking services have some type of macular disease. The dry form of macular degeneration is most common, followed by the wet form – inherited forms.

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.

Reduced Contrast Sensitivity

But the other major cause of functional limitations is reduction in contrast sensitivity (slide 32). We don’t hear about that as much. And information in the image is defined by contrast (slide 33). Whereas, if visual acuity is lost, it looks blurred. When contrast sensitivity is lost, it goes away. You don’t see at all.

And when patients experience the loss of contrast sensitivity, the way they will describe it is glare. Okay, and here’s a simulation of what it looks if you lose contrast sensitivity (slide 34). The only difference between these two images – well, the two differences – one is this is blurred to 20/200, the same as the other one was. But in addition, the contrast of the image is uniformly reduced, as if you lost contrast sensitivity by about – I guess it would be on the order of about 28 log units.

The way contrast sensitivity is measured is with an eye chart, but the letters are all the same size. It’s called the Pelli-Robson Chart (slide 35). All the letters, [which] are set up between the viewing distance and the size of the letter, [are] the equivalent of about 20/400 or 20/800 letters, they try to make them as big as possible. But what varies as you move around the chart is the contrast of the letters.

If you have perfectly normal contrast sensitivity, you should have no trouble reading the letters right here [pointing to bottom of chart]. What you do is just see how far down the track you can read. And each contrast varies in a tenth of a log for each triplet of letters (slides 36 - 42). So you specify contrast sensitivity really as a ratio of the light-to-dark. If the letter’s absolutely black, there’s no light coming off of it, the contrast will be 100 percent, no matter what the background is, as long as it’s not black too.

Contrast is not the same thing as brightness. You can’t improve contrast simply by turning up the intensity of the light. It’s the ratio of the light to the dark. If you turn up the intensity of the room lights, you’re going to reflect the same ratio from the two things. What improves as you turn up the light is your sensitivity to contrast. At low light levels, contrast sensitivity is worse for everybody, whether you have low vision or not; at higher light levels, your contrast sensitivity is better. There are many ways to specify that ratio (slide 43). We won’t go into it. It’s just a light-to-dark ratio which formally you want to use. And it’s important to remember that it’s – those of you who are illuminating engineers – reflectance determines the contrast not the overhead light.

Contrast Correlates to Visual Acuity

In this population [i.e., patients], contrast correlates with visual acuity. If you lose your central vision and you’re forced to use your peripheral vision to do everything you used to do with your central vision – everybody’s contrast sensitivity is worse in the periphery than it is in the center; everybody’s visual acuity is worse in the periphery than it is in the center, so the two tend to go down together more or less (slide 44). But there are people who can lose more contrast sensitivity way out of proportion to the visual acuity loss and vice versa. So even though they correlate, they do have independent effects. I’ll show you those.

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.

Effects of Lighting and Daylighting on Performance

Most patients self-report their vision quality is quite poor – in poor ranges, over 90 percent (slide 49). And important to you is when we ask them, what kind of affect does lighting have on your performance activities? Close to 70 percent say it has a major effect. Lighting is one of the biggest problems. Over 20 percent say moderate effect and only 11 percent say it has no effect. So lighting is a very important consideration.

Question by [Participant]: Day lighting?

Response by Bob Massof: Yeah, daylight – both too much and too little. Too much light and they tend to wash out from this glare. Too little light their sensitivity is reduced and what might look like mood lighting to the average person can be a funhouse.

Other Health Problems with Low Vision Patients

Okay, the other thing to keep in mind is these people are old and they have other health problems. More than half or two-thirds will report they’re in good to excellent health when they come to the clinic (slide 51). Of course, we don’t see the ones that can’t get to the clinic to go to get help, so there is a bit of a sample bias here – and that’s true for all ages.

Frequency Distribution of Health Problems

But when you ask them about their health, they have all the same diseases that anybody in that age group would have (slide 52). They report diabetes, heart problems, heart attacks, high blood pressure, neurological problems. Back pain is a real common one. Thirty-percent said they have back pain.

These co-morbidities that you have to consider [as part of] the overall health burden that this population has. And you’re adding a visual impairment on top of all the bricks they’re carrying. So the effects of visual impairment in this population can be magnified compared to the effects in a younger population. A lot of times compensation is more difficult, because of the other things they’re dealing with.

Cognition and Emotional States

I think given the time limit, you can scroll ahead, because I want to make a particular point about – let me just say one thing is that depression is also a problem with this group (slide 53). Thirty percent of people with low vision have clinically significant depression and they become isolated and don’t go out. A lot of this is related to fear of falling (slide 55), not getting outside the home. Life space shrinks down to very few social interactions.

Falls and Injuries

So talking about falls: Just in general, if you look at the epidemiology literature, there was actually a Safety and Seniors Act that was passed in 2007 or 2008. It was called the Act of 2007 of Putting Emphasis on Preventing Falls and Injuries in the Older Population. But a third of the people who reach 65 have fallen at least once in the preceding year (slide 64). About a third of the people over 65 have a strong fear of falling and that limits their activities. And this prevalence of both falls and fear of falling increases with age.

Well, in terms of hip fractures, 90 percent of the hip fractures occur in this population because of falls (slide 65). Visual acuity loss turns out to be a major independent risk factor for hip fractures. I’ll give you those numbers in a minute. Relative to people who have 20/20 visual acuity – if you test for all the other variables – hip fractures double in the acuity range of 20/30 to 20/40. They triple in the range of 20/50 to 20/70. We’re not even up to Medicare paying for it. And then once you get up into Medicare’s definition of low vision, it quadruples. So you have four times the risk of hip fracture if you have low vision by Medicare definition than you if you don’t – all else being equal.

Accidents [are] the leading cause of death in seniors; falls account for about 50 percent of accident of deaths, car accidents account for the other 50 percent (slide 66). The death rate from all causes increases 20 percent for people who are 20/25 relative to 20/20 (slides 67 and 68). It goes up to 25 percent more for people who are 20/32 – it’s just a small change, one line. And less than 20/30 – that’s not even into what we conventionally considered a low vision category – 20/40s kind of important. They take your driver’s license – put restrictions on your driver’s license. The death rate is 60 percent higher. So the 30 million figure might not be too far off if we’re thinking in terms of the impact it could have on safety.

So probably the reason for this is that as you age, you get nerve degeneration occurring in the vestibular apparatus. That’s the inner ear that controls your balance (slide 71). And you also get nerve degeneration occurring in the stretch receptors and appropriate receptive feedback that you’re getting from your muscles and joints (slide 70). And making your balance – three systems are involved: your vestibular system, which senses accelerations; your receptive feedback from your muscles and joints and your vision (slide 69). [These] are called flow fields that tell you that you’re moving relative to your environment. If you have two of those three systems intact, you can control your balance. If you drink a lot, that screws up the vestibular system, okay? But it also, in doing that – because of dehydration – it also induces what we call vestibular-ocular reflex that, for kind of a nice name, we call it getting dizzy. And balance tests tend to be good diagnoses that you are having too much to drink.

If you lose two of these systems, you cannot maintain your balance. If we have just neurodegeneration going on, we’re probably increasing the load on vision to maintain balance as we grow older. Added to that, neural-degenerative diseases like peripheral artery disease and things like that in this composite, and so [there is] more reliance on vision. And even so, small changes in vision seem to have a big impact on both.

Mobility

So we can get more or less back on schedule, I’ll not go through the details of these other slides, except to show you that for all functions, they decrease pretty systematically with visual acuity and with contrast sensitivity (slides 72 – 77). But notice that mobility is very poor to begin with. Normal here would be about five. So even for people with very good contrast sensitivity and going back even for people with very good visual acuity, mobility is the worst affected and it stays bad. And as the vision gets worse, the other functions come down, but mobility gets clobbered early and stays clobbered. And blind spots do the same kind of thing. Mobility gets clobbered early and stays clobbered. These are all independent effects.

So the focus really has to be – the biggest bang really has to be on mobility (slide 78). And what can be done – I’ve already heard people talk about; I don’t think I’m going to tell you anything new – but increase contrast. Glass doors are not good for people who have visual impairments; reduce camouflaging clutter. Increase the light, but not too much; you want to reduce glare. What that means is get the light sources out of the line of sight, okay?

Increase safety is a big part and we saw pictures of stairs and other things. And the emphasis here really has to be on steps, stairs and drop-offs. That’s where the falls occur, either on the top of the steps or the bottom of the steps or off a curb. And the changes in surface elevation – ramps on sidewalks – these types of things. Even on a small ramp to go up to change a level can be a deadly hazard for someone who can’t see that transition. And transitions from surface texture – going from carpet to tile – can be a tripping hazard. To people who can’t see that texture change, that could increase the risk.

Discussion

Question by [Participant]: The concept of glaucoma affects glare. Is that correct? Is that because it diffuses the light in the fluid of the eye?

Response by Bob Massof: No. Two things seem to affect glare. One – and you guys will correct me – one is optical. So if a glare source is off axis for anybody – it doesn’t have to be somebody with low vision – it’s called disability glare. That’s just scattered light inside your eye. Okay, the light hits the back of the eye and bounces around inside the eye and it causes what’s called veiling luminance and that washes out the contrast of the image. Okay, so that’s a form of disability glare. For anyone who has something wrong with the optics, whether you have dirty glasses or your tear film is too full of mucus, or there’s something that is having optical affects, that scatter gets even greater. If you have a cataract, especially nuclear sclerosis, you get even more scatter. So those types of things just wipe out the contrast. It will wash things out just from having that glare source there. That’s from having just a bright light that’s in the line of sight – even if you’re not looking right at it, it’s off to the side – if it’s visible, the light is getting in through the pupil and it’s going to have an effect. Now, people with glaucoma do get cataracts. But also, there’s some neural adjustment that occurs – being able to compensate for the scattered light neurally in the retina. Glaucoma is one of the conditions that can [cause patients to] become more sensitive to glare, as well as macular degeneration.

Question from Fred Krimgold: I noticed that the tests you referred to are all static. And one thing that I was concerned about is that vision in a dynamic situation, like traffic or mobility, is very different from simply accumulating cues and being able to read a chart. Are there measures that give you a sense of that dynamic function in vision?

Response by Bob Massof: Well, there are measures. Certainly, a number of measures that are used in research studies, used in a laboratory to study the dynamics of vision. There are not very many clinical measures. But in many cases, you’re really not trying to answer that question. It’s more you’re trying to deal with identifying the stage of the disease or the impact of the disease on the vision. So these are used as indicators of where –

Comment by Fred Krimgold: Well, the particular case is that the driving test is a static test. Driving is not static. And also, as you mentioned, mobility. When we look at wayfinding and other situations in which low-vision people find themselves, they’re adequacy or their functionality is dependent on being able to function in a dynamic situation, which is quite different from the measured static situation.

Response by Bob Massof: Right.

Comment by Vijay Gupta: Over the years when I [have had] – according to what I heard – my low vision for 30 years. And I’ve been through John Hopkins, through NIH and many other places, but what I’ve found [is] a big disconnect between the medical profession and the design community of buildings. That’s the basic comment that I have, because I will get into more a little bit later.

Performance and Productivity

Comment by Tom Williams: It’s interesting to me that there doesn’t seem to be any more research out there on the connection of daylight to productivity. That’s almost amazing, that scientifically there isn’t any kind of support for that.

Response by Mariana Figueiro: Measuring productivity is really hard.

Comment by Jeanne Halloin: The Heschong-Mahone Group out of California has other daylighting research on productivity, both in schools, and then they also did one in Wal-Mart where in the daylit areas, no matter what was being sold there, they sold like 50 percent more in the stores. So I think there are two other studies that -- if we want to start talking about daylight -- that we could look at.

Response by Mariana Figueiro: Actually, that study was the one with the schools that the National Academy questioned. So there’s still some debate about the Heschong study. Some people agree with it; other people still have some questions about the data, how the variance explains the data and so on. In [the Heschong study] with performance in offices, they weren’t able to replicate with daylight. Measuring productivity is really hard, especially measuring productivity in the field.