Visual Acuity Testing, Part 2: Acuity Cards and Testing Procedures

Chapters:

1. Introduction
2. Modification of the Acuity Card Procedure
3. Testing People with Visual and/or Multiple Impairments

CHAPTER 1 — Introduction

MAYER: About in the '80s, people were really interested in using various techniques, electrophysiology but of course behavior, to measure visual functions in babies that had visual problems. And particularly to measure visual acuity, which is the most important, probably, most important visual function that you can measure in an individual with a visual impairment.

And there were a number of different researchers who were interested in this and in doing this, modifying procedures and so forth. And at that time, in the '80s, I had finished my dissertation, my OPL research, and came to Children's Hospital in Boston to work with Anne Fulton, who was the first ophthalmologist to bring FPL into a clinical setting. And she did that with Velma Dobson's collaboration.

They brought an apparatus, which I help set up at Children's Hospital in Boston in '79, I believe. And they did some feasibility studies and showed that you could actually use it to test babies using shortcut procedures. You couldn't do full psychometric functions with babies in a clinic because you can't spend days testing their vision. But you could do it with shortcut procedures.

Teller was having troubles about our using FPL and OPL. I brought OPL to Children's Hospital and we're able to test most kids with that. Not everybody, but a lot of kids. But she felt there were problems with bringing FPL and OPL into the clinic and using it to test babies. And she felt that there really needed to be a real clinical test of visual acuity that could be applied in all kinds of clinical settings.

And she did something quite shocking to those of us who worked with her because she went against her psychophysics and against the scientific basis of FPL and OPL. And she did away with it. And she said there's a lot of information that observer is getting from the baby that doesn't get conveyed, it doesn't get used in forced choice preferential looking.

For example, those very strong looks to big stripes and the subtler looks to smaller stripes and the subtle things that babies do, because sometimes they raise their eyebrows when they see stripes, and maybe that's a strong cue that, yeah, they really saw and were interested in the stripes. She felt that subtle, more subjective information could be translated into a test where the observer now controlled the testing.

And how did they do that? She had the stripes mounted on gray cardboard where the stripes were in one position and that gray stimulus was still over there and it was a gray surround and a gray card. So the stimulus was the same, but the stripes were on individual cards. Every card had a different sized stripe. And the observer was to use those cards in whatever way they needed to, to find out if the baby detected the stripes. No longer was she saying the stripes were on the right or the left.

NARRATOR: A photograph shows Davida Teller with a number of rectangular cards fanned out in front of her. The width of the stripe stimulus varies from card to card.

MAYER: Well, we were really upset because we felt that put too much control into the hands of the observer, who could be biased. We were observers, after all. And as somebody looking at a little baby, you want them to have 20/20 vision.

So you're going to say we felt that baby sees that card, of course. And Teller said, "Well, yes, there is the problem of bias, "but the procedure can be designed so that you minimize bias."

And how do you do that? You keep the person showing the stripes ignorant or unaware of where the stripes are until the person finishes testing. Test this stripe multiple times showing it to the right and the left, making sure that they think the baby sees it because the baby looks strongly that way, flip the card, the baby looks strongly this way, flip it again. The baby looks strongly that way.

"I really think the stripes are there." Check, "Oh, I was right." And that kind of information the observer could keep themselves objective to a certain point, then confirm their judgment, so give themselves feedback about it. The corollary of that is that if you didn't think the baby saw the stripes or you weren't sure, you didn't check the front because you could really be biased by that.

There are only two choices, after all. So 50% of the time you could guess it correctly and the baby's not seeing it. So those two controls really, really answered the question about controlling for observer bias, at least to some degree.

The first iteration of this was to present these cards in an apparatus very much like the forced choice preferential looking apparatus, but a portable one that could be put on a table. And we called it a stage because it turns out it looked sort of like a puppet stage. And it had a rectangular window in the middle, behind which the cards could be presented and moved away and then flipped and presented again.

And so that made it very convenient and made it pretty easy, easy to fit on a table in some room. You could close it up, it was portable, you could put it away.

One really wonderful thing that happened was that window. Because now that window opened the observer's view and the baby's view of the observer and also to a puppet show. So often we would hold up a little puppet to keep the baby's interest or sometimes our face looking at them was enough to look through that window. And then the card would go up and the baby would still be looking, sometimes waiting for you to show up again, so you had to be a little careful about how animated you were.

That's one of my problems is I would sit there and play with the babies, but not do my test.

NARRATOR: We see a video clip of Luisa Mayer administering an acuity card test to a young boy. The boy sits on his mother's lap in front of the stage as the cards are presented to him in the window. When the cards are removed from the window and rotated, the observer is able to engage the child's attention before presenting the card again in a new orientation. The child is observed through a peephole in the middle of each acuity card.

MAYER: But that was a great, really clinically important thing that happened just by chance, essentially. It wasn't planned, so it was really, really nice. So essentially the acuity card procedure — which is what it was called — wasn't very much different in terms of the stimulus and the presentation mode and the observer's task, in a sense, from FPL, except that all of the psychophysics and all of the counting and percent correct and statistics that were done didn't need to be done.

In the '80s, Teller and Dobson and their colleagues in Seattle did a number of studies of the ACP, the acuity card procedure, essentially to show how or to find out how did it compare with FPL and OPL, and it turns out the norms are very close. They agree rather well. And in a direct comparison between FPL and the acuity card procedure in babies with visual problems, it turned out they agreed remarkably well.

These were monocular tests, you know, babies being tested one eye at a time. They also discovered that test re-test reliability was pretty good, which is very important. You need to know you're going to get about the same answer. Well, it isn't about the same, it can vary over a range, but they found that out.

The other thing that was very useful was they did a study of feasibility, that is how does this work? How does the acuity card procedure work in clinical settings?

And they went to ten diverse clinical settings, one of them being Children's Hospital, where I was, struggling away doing OPL with babies. And so we started using it at Children's Hospital, and a number of other people did. And we found it was a great test. It was a fabulous clinical test. We could test really rapidly, we could get a measure in each eye of a baby in ten minutes or less. Whereas it would take 30 to 40 minutes — well, sometimes 20 minutes in a really good baby — to do OPL thresholds with them.

The equipment was easier to handle, there wasn't all that calibration of stripes that I had to do. It was just altogether good. There were a lot of babies we could test now that we hadn't been able to, so it was wonderful. We loved it. And we weren't the only ones.

CHAPTER 2: Modification of the Acuity Card Procedure

MAYER: The thing that we discovered at Children's Hospital when we started using acuity cards was that we didn't, we could test more easily without the stage. We could present the cards now in the baby's position, in wherever we needed to present it for them to see them as easy as possible. And for us to make their observations as easy as possible too.

NARRATOR: In this photo, Davida Teller is on the left holding her grandson while the baby is being shown a Teller acuity card by his father, Davida's son, on the right. He holds the card horizontally, the standard way of presenting acuity cards. Note how strongly the baby gazes at the grating.

In a series of two photos, we see a young boy being held in his mother's lap while an acuity card is presented to him. The card is being presented in a vertical rather than the usual horizontal orientation.

MAYER: For children who have very low vision, who if you hold something at too far a distance they can't see it very well, we can get quite close and we can show the stripes right to their face, very close. And we can observe their behavior. So taking the cards out of the apparatus was another revelation.

So the first revelation was that operant preferential looking apparatus could be put in the closet, and the second was the stage could be put in the closet. And that freed up really precious clinical space, which has gotten even worse as years go on and as more things are being done in clinical spaces. So now the cards are just set on a table, they're available to me whenever I want to pick them up and show them to a baby. I don't have to do anything fancy, I just store them carefully with a cloth over them and so forth.

NARRATOR: In a video clip, we see a demonstration of an acuity card test being administered to a very young boy. The boy is in his mother's lap as she sits in a chair across from the observer, Luisa Mayer. The cards are quickly presented, and then reoriented. Sometimes the observer looks through the peephole, sometimes she looks over the top of the card. When she feels that she can determine which side of the card the stimulus is on based on the child's cues, she checks to see if she is correct before moving on to the next card.

MAYER: And all patients that I see now with my colleague Barry Kran in the New England Eye Clinic at Perkins, we always test babies' and young children's and older patients' acuity using these acuity cards unless they can do recognition acuity. And recognition acuity means acuity for symbols or letters. If they can name or match those, then we always do that test.

NARRATOR: We see a logarithmic visual acuity chart, a chart with 14 lines of five letters each. The size of the letters diminishes in a consistent progression from the line of large letters at the top of the page to very small letters at the bottom.

MAYER: The reason for that is — why is it important to always do letter or symbol acuity rather than acuity for stripes — is there are some conditions that stripes are not very good at detecting the basic underlying problem. We know that, we've known that for years. We've known it actually back when we did operant preferential looking acuity testing. And there are some that it's very good with. So we always want to test recognition acuity because it may not get the same answer.

The stripe acuity will not necessarily be the same as the recognition acuity. I'm going to test your acuity with acuity cards. And I'm going to start with big stripes and show them. And I'm looking to see whether you look at the stripes.

Yeah, you looked at them really strongly over there. Let's see if I can see. Oh, yes, and now he's looked to his right, to the left. I think he probably sees that stripe because he looked so strongly in two trials.

Oh, I was right, the stripes are there. Great. Now let's make the stripes a little bit smaller and see if you still are going to see them. Oh, he looked to this side. Very good. And now I'm going to flip it. And he looked to that side.

Okay, pretty clear, but just in case. Yes, all right, I think the stripes are on his left. And I was right, ah, great. So now I'm going to show you a much smaller stripe and let's see whether you see this one.

Okay. Oh. I think maybe you don't see it because you're looking back and forth between stripes. Maybe holding a little bit longer on one side. Okay, that's pretty subtle. Let's flip it and see what happens when I put it on the other side. And going back and forth again, back and forth.

I can't tell where the stripes are based on what he's doing. Because now he looked to the same side again. And the stripes were flipped, so I'm not going to look at that card. I'm going to say he doesn't see the stripes on that card. I might go back up and test the next higher level, the next size up, make sure that's your threshold, come back to this one again.

So in the acuity card procedure we may go back and forth around threshold many times to be quite sure that we've got the smallest stripe the baby sees, or the person sees.

CHAPTER 3: Testing People With Visual and/or Multiple Impairments

MAYER: At Children's Hospital we got a grant from NIH to develop monocular norms — that is, right eye and left eye norms in children.

NARRATOR: In a video clip, we see a young boy whose monocular acuity is being tested using the acuity card procedure. He wears a patch over his right eye and sits in his mother's lap as the observer presents the acuity cards into his field of vision.

MAYER: Those norms we use now to interpret babies' acuities. The other part of testing that's really important is do we get the same answer time after time? Is there a change in acuity if there's been a disease or a progression of a child's lazy eye, is that showing up as a reduction in acuity? So it's important to have normative values for that too. And that was one of the things that we got in this norm study was that information.

NARRATOR: We see the results of an acuity exam given to a 12-month-old child with a diagnosis of a cataract in the left eye. When the child's monocular acuity was plotted on a graph that displays established norms, we can see that acuity for the right eye is within the normal range, while the acuity for the left eye with the cataract was well below normal.

MAYER: So I'm now at New England Eye Institute Clinic at Perkins. And with my colleagues we test babies and babies and babies and children of all ages, and handicapped people and all kinds of people who cannot cooperate with, or who can't do symbol or letter acuity tests. And we compare their acuities to normal acuity for age.

If we can test their letter acuity or their symbol acuity, of course we do. It's really important. But many of the children we see we cannot. When you're testing a child that has cerebral palsy, for example, that has a neuromuscular disorder, and they're sitting in their wheelchair and they're positioned in such a way it's very hard to get them to position properly with the stripes, with a test of their acuity.

So having the cards, in fact, having the cards where we can take it out of the apparatus and present it to them in a comfortable way in their space where they can see it easily was really a revelation.

NARRATOR: In this photo, an infant with cerebral palsy is supported by his mother on a bean bag chair on the floor. Dr. Barry Kran, seated on the floor to the left of the photo, shows the infant a grating on a Teller acuity card.

In the next photo on the right, Dr. Kran presents a Teller acuity card to a multiply-impaired adult patient who is seated in her wheelchair on the left of the photo.

In this video, the boy's acuity is being tested by Dr. Kran using Teller acuity cards. The boy shows that he detects the grating by looking and pointing to it. Dr. Kran judges when he is unable to detect the grating by his looking and pointing to both sides of the card. He has to come very close to the card to see the grating.

MAYER: Now, using those pieces of information about normal development, about the normal variability of testing across time, normal variability between eyes, then we can go and interpret acuities in patients who have ocular disorder. So we have a baby that has a cataract in one eye, normal other eye.

We can say, is the acuity in that eye poorer than this eye, significantly poorer? And then does that have implications for treatment? So the test is really useful for diagnosing and managing ocular disorders and visual impairments in young patients. And older patients as well.

In fact, the acuity card procedure is being used all over the world in research settings and in clinical settings as, I would say, now the standard test of visual acuity for babies — behavioral visual acuity.