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Getting to 1M: Understanding Magnification and Print Size
[MARY ZATTA] Hello everyone this is Mary Zatta from Perkins. Welcome. We are just waiting a few more minutes for the rest of the attendees to join us. We will be starting at approximately 2 PM. So, hang on. We will be getting started in about one minute. I think we are ready to begin. Hello, my name is Mary Zatta and I am quite excited to welcome you to Perkins’ first webinar. This has been an initiative that we have been working toward for some time. We have a lot in the works for future online professional development activities. If you are interested in getting information about future webinars were teaching resources content which includes publications, newsletters, webcasts, etc., please go to www.perkins.org\resources.
Before we get started I would like to review a couple of things. First of all, if you do not see the welcome screen, click on the edge of the connect icon at the bottom of your screen. It looks like several people are attending this meeting. There will be time reserved at the end of the webinar for questions. Please feel free to post your questions in the Q&A box during the webinar and we will address them later on. All interactions for this webinar will be via the Q&A box. There will not be any questions via the phone line. You may see a pop-up screen asking you about how you will choose to receive audio for this webinar. If you do see that, just click on the cancel button on the screen.
If you're using your phone, you should mute your computer speakers so you don't experience feedback. Thank you for joining us for this event. Please know that we will do our best to ensure that you have a good experience as you attend this webinar. Also, one more thing I want to point out is that you will see that there is a handout that Darick has prepared for this webinar that you can download within the meeting room. And now, it is my pleasure to introduce Darick Wright, coordinator of the New England Eye Clinic at Perkins, as he shares his expertise with us on getting to 1M, understanding magnifications and print size. Welcome Derek.
[Recording starts here]
[DARICK WRIGHT] Thank you, Mary. It is good to be here. And thanks to the educational research program at Perkins and the team that has been assembled here to help us out with this daunting privilege that I have to be the first Perkins webinar. Selecting print size is really a complex process. I want to be really up front today and say that the kind of things that we will talk about today are not meant to replace, in fact they are meant to complement the assessment tools that are already out there. The things we are talking about are really meant to go along with a learning media assessment or a functional vision assessment. Therefore, I think this will be a review for many of you, but also maybe a new way of looking at the selection of print sizes for some others of you.
I've divided this presentation into three primary areas. The first section I will talk about how you can use a near visual acuity chart as an information tool to gather print size information. Next, I will talk about what are some considerations when determining appropriate print or symbol size. What are some characteristics of print that you need to be thinking about as a TVI, as an O&M specialist, and as a low vision therapist, in helping your student access the curriculum. And lastly, we will have a very brief overview of what are some basic methods of magnification. So, backup, we have to talk about anatomy just a little bit.
What you're seeing now is a picture of the back of the eye or the Fundus. You will notice there is a bull's-eye in that picture. The very center of that bull's-eye is the Macula and Fovea, the portion of the retina that gives us the greatest detail. That's what gives us the 20/20 visual acuity. It’s the densely packed photo receptors in that area that allow us to resolve detail. As we move further and further away from the Macula and Fovea area, we are still able to pick up details, but just not as well. So our visual acuity decreases the farther away we get from the Macula and Fovea.
All of the signals that are received in the retina then are sent to the optic nerve, and it’s the optic nerve’s responsibility to transmit that information to the brain via the visual pathway. Obviously, if there's any impairment, whether it's the refractive quality of the eye and focusing those images onto the Macula Fovea in the retina and then the optic nerve in the brain, any interruption of that will cause some sort of visual impairment.
Doctors are going to be looking at the health of the retina, the health of the Macula and the Fovea in several different ways. One of the ways they will look at that is by testing visual acuity; how well can someone resolve detail. And so, looking at it from a clinical perspective, they will give the person a chart to look at with letters, symbols or numbers. And they will usually use a defined distance, typically 40 centimeters, or about 16 inches. Or they may have that person hold the chart at a preferred distance.
There's always some sort of predetermined or set distance that the person will be looking at the near visual acuity chart. The next thing they will do is ask the person to read the smallest line possible, the very smallest letter or symbol or number that person can identify. That is what is called threshold acuity, and I think that is really critical for all of you to understand because I did not always get that when I was out in the field. When you see a clinical visual acuity written, it is a threshold. That’s how low can they go. That is the smallest a person can resolve or identify.
The next thing to know about a more formal clinical visual acuity testing is it is done under the optimal conditions. It’s done with the best correction possible – glasses or contact lenses. It is done with good contrast and under optimal illumination as well. It's not always the same kind of conditions that we find in real life and in the classroom.
Now, how is that noted? This should look pretty familiar to a lot of you if you are reading an eye report. Typically, it will be noted as what’s the size of the optotype or that letter, symbol, or number, and then the distance. So what you see here, it's 2.5M and tells us the size of that letter, symbol, or number, the size of that optotype in M notation, or an M-size. And obviously 40 centimeters tells us the testing distance that the person is holding that chart. Now, 2.5 M may or may not mean anything to you. That is something we will be talking about today. Certainly, 1M should mean something to those of you who are teachers of the visually impaired or orientation and mobility specialists, because we know that 1M sized print is the same as regular sized print. If I can read 1M size print, I should be able to read a newspaper.
So, we've got that. But the question is what is 2.5M? I know it’s bigger than 1M, but how big is it? Here’s where I might be able to help you out a little bit if you've not already figured this out. You've got to get a near visual acuity chart because there is a wealth of information on there that is going to be able to help you understand how big 2.5M is. How big is that smallest line that that person can read in the doctor’s office or that’s written in the doctor’s chart?
This example that I've given you here happens to be a Patti Pics™ chart. It can be any other near visual acuity chart; I am just using this one as an example. What I want to point out on this chart is the information that is there. On this example, on the left column, there is the M-size of the corresponding lines of symbols. If I look at the very top; circle, square, heart, Apple, circle, then I have a corresponding size to that in M-size. I have on the right-hand side the distance equivalent to that. We will use that a little bit later. But just note for right now, looking at a good near visual acuity chart, not only do you have the symbols, but you also have various sizes, or various equivalent sizes.
Back your question, how big is 2.5M? Now we have some tools to do that. Grab a ruler, find the corresponding line on that chart, the 2.5M sized line on the near acuity chart, and measure it with your ruler. I like to use millimeters. I've never been great with fractions, so millimeters are a little bit easier. Also, millimeters will be a little more accurate, particularly as you get to measuring very small things. In the example here, a 2.5M sized symbol is equivalent to about 3 millimeters in height. So now we ‘ve got a unit of measurement that certainly I can understand better and I can certainly measure better than 2.5M. Sometimes, if you're looking at the doctor’s chart, it's not going to be written in M-size. Instead, it’s going to say, “Darick can read 20/125 at 40 centimeters.” That is my near visual acuity. What does that mean? How does that translate into a print size? I'm going to say, let's go back to that chart again and find the column that gives you the distance equivalent, and find the 20/125 line. I have done that for you in this example.
The next thing you're going to do, once you find the line, the 20/125 line, you're going to find the M-size. The chart should tell you what that is. If all of you were here, I could ask you the question and you could tell me, but I'm going to tell you, 2.5M. We already know how big that is, 3 millimeters in height. This is another way to use a near visual acuity chart as a tool to help you decode formal visual acuity and help you understand more about approximate print size.
We are not done just yet. What we have done so far is we’ve taken that formal notation and figured out how big it is in millimeters. But remember, I said that is threshold acuity; that's how low someone can go. Most of us are not going to be able to read very tiny print for a sustained period of time. So as vision educators, what we've also got to determine is: what is the appropriate print size for a student that they can sustain for any period of time? Here is another way that you can use that same chart to help you out. In our earlier example, we said that 2.5M was the threshold, the lowest or the smallest that a person can identify at that testing distance, 40 centimeters. Visual reserve is something, then, that says, probably a person is going to function better if that print size is two to three times bigger.
So I will use my chart here to find the 2.5M line, and then count up two to three lines higher on that chart, and that will give me an estimated functional size. In my example here, that estimated functional size is going to be either 5M or 4M. So the threshold is at 2.5M, but I'm going to estimate or predict that maybe my student will be able to function better at 4M or 5M from that reading distance of 40 centimeters. Hopefully this is making sense to you. If not, I'm going to encourage you to write in on the Q&A section and the team here will help get your question answered.
Now that we've got this information, we’ve got the threshold, we know what size it is using millimeters, and that’s the unit of measurement that we can all understand, and we have estimated what the functional size might be, we’re going to take that information and combine it with the data that you are getting from your learning media assessment, which could include their reading efficiency skills and information from the functional visual assessment.
Moving on here, we might end this a little bit early and have plenty of time for Q&A. The next session I want to talk about is going to be what are some characteristics and considerations that you need to be thinking about as you select an appropriate print size or print style? I put this slide here and we’re going to be talking about typography, meaning that in this part we are talking about the units of measurement of print, what about serif versus sans serif, and what about leading and kerning. You may or may not be familiar with that term as well. This next slide, the only reason I put that up there is to say that point size is that one unit of measurement. We are certainly all very familiar with that, particularly on the computer. What size point can a person read? What do they prefer? 24 point, 12 point. That is great, but I am here to tell you that it is not a standard unit of measure. It really started within the printing industry. This slide is showing you that, as a printer, they developed a unit of measurement called point which also correlated into another unit of measure called picas.
Personally, I don't find the point system particularly useful because it varies. Point sizes are going to be slightly different with one font style, such as Times, versus another font style, such as Ariel. So as a consistent unit of measurement for me as a vision educator, it doesn't really help. The other thing that I struggle with is the same thing I did with M-size. I kind of have a concept of how big 24 point is, but I don't think I could pick it out on a piece of paper very well. Personally, as a unit of measurement, I have a hard time with it.
Serif versus sans serif - what are we talking about here? A serif typeface, or another word for typeface is font, means that it has a tiny strokes or feet attached to the edges of the letters. Other than just looking pretty, it is also designed by type creators to help guide the word from one letter to the other. Some examples I have given you on my slide here are Times, Script, and Bookman are all different typefaces or type styles or fonts that are serif and have those little feet attached to it.
Conversely, a sans-serif type, means the absence or without serifs. These are often used in headlines for visual impact. You will notice in my examples here; Arial, Century Gothic, Helvetica. You don't have the little curly q’s; you don’t have the little feet. It is not guiding the eye from one letter to the next like the serifs do, but it really simplifies that letter. Here is a simulation to give you the difference between a serif and sans-serif. At the top is a serif font style in 14 point. The bottom is a sans-serif font style in the same point size, 14 point. And I have blurred them equally. For many, the sans-serif font on the bottom appears easier to read and may be brighter than the serif example at the top. It doesn't have all the extra little lines that the serifs do that make it appear a little bit darker, or some people find it slightly more difficult to read. So leaving serif and sans-serif; let’s talk about leading.