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

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.