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“If you’ve got the money to spare, and it’s a lot… so I get that. So it’s not highly accessible to anybody, but the beauty of the computerized test is the specificity because the person is wearing an IMU. So the first thing that’s going to happen is you’re going to establish their static visual acuity relative to the computer. And even though you’re looking at a computer, it is calibrated to be far vision, when they’re in the tests piece. And so you’re going to get static visual acuity and the person is telling you about a target that’s flashing. It happens to be the capital letter E. So now the computer says, well, this is what your static visual acuity is. Now we’re going to take that and make it a little bigger and see how long it takes your brain to see something, to know what it is, and it will be relevant in the next piece.
But that visual perception time is measured in milliseconds, because when you get to the dynamic visual acuity, it is a set velocity, and in the computerized world, that happens to be the minimum. The target velocity is 100 degrees per second. You will get the target and I’ll explain what that means in a moment, anywhere from 85 degrees per second, to 120 degrees per second. So it gives you an error window. It says, this is an okay amount of a variation. But what happens in the computerized is, I’m looking at a blank screen or a target area. And until I’m in the target range, that E will not flash. So I know my head is in motion when the E flashes… or my athletes head is in motion and they’re going to tell me which way it was pointing. And then from that, it will give me the dynamic visual acuity when my head is moving to the left or when my head is moving to the right, when my head is moving upward or when my head is moving downward, that’s the specificity of the computerized world.
Now the dynamic visual acuity on an eye chart, low-tech is fine, and it’s great… if that’s what you have accessible, that is the thing to use. The difference is, it’s a fixed target and they can see it the whole time, right? The only issue would be is if I’m turning my head and I’m reading it at X, Y, Z, I’m reading it in the decelerated before I’ve accelerated. So it’s almost a pause. So you can’t always… even if a person’s not trying to get through a test and lie to you about how well they’re doing… they may. It’s just the brain’s natural ability… wants to perform. It wants to do what you want it to do, and so it’s going to try to read the letter when it can. And so that’s the beauty of the dynamic visual acuity. Now, the different… that’s the upside on the computer side, but that fixed. So it’s a fixed velocity and a changing letter. And from 3 to 85… we know that ages 3 to 85, 2 lines or less is within normal limits. So that’s the rule we take.
So if you have 20/20 vision, you should be able to move your head 100 to 120 degrees per second, and read up to 20/32 and still be normal. Now the gaze stability test flips that. It takes the E that… it takes your static visual acuity… it automatically raises it two lines. So it would take my 20/20 E and make it 20/32. Then it says, how fast can you move your head and still know what you’re seeing? And that, for me… I’ve evolved to find that to be more functionally applicable, because it will start really slow. We know that basic activities of daily living start… you can get through a whole day and never do better than around 120, 130. However, there have been people come along with that test and establish norms by age. Well, this is non-athlete normed under the age of 60. I use the Brian Ward Study and I target that at about 155 to 160 degrees per second. Well, if I’m only testing at 120 degrees per second, I could miss a functional deficit.
Okay. And he goes under 60, over 60. It is simple for me. There are other studies that do it by decade. Anyway, that’s my simple… the other thing. So then when you turn it, now you know what the norm does, not what our athletes do, because that’s the even trickier part. I think dealing with athletes around gaze stability, you really have to be… you can miss a lot if you’re only testing at 120. And I say that because we tested 137 minor league baseball players, age 17 to 31, their average was 220 degrees per second.
It is. And some Of them performed as… I mean, the range was quite low. I can tell you that those people probably didn’t get stay in camp, but they were quite low up to 365 degrees per second… was our fastest guy. Amazing and very fatiguing on your arms if you’re the tester. So, you could easily miss an issue if you’re testing way down at 120 degrees per second. We also happen… in writing almost for submission, the under-18 athlete. Well, they come in-
I know. They come in at 186 to 196 degrees per second. That’s, again, not far off their adult counterparts. That’s one of the things I like about that test. As I mentioned earlier, you can go down to kid… really young kid. It’s one of the few objective tests I have for little bitty kids that are neuro-typical and active. What can they do? But anyway the youngest athlete I’ve ever tested is seven. But anyway… whether you call them an athlete or active playground user, I don’t know, but this kid was better than [inaudible 00:06:29]sport, let him go. So again, the value of gaze stability is that it’s looking at how fast your head can move and it’s going to come out very different.”
RESOURCES & LINKS:
Amy Alexander, PT
Amy is the primary vestibular physical therapist for Banner Sports Medicine and Concussion Specialists Clinic, a physician led multiple discipline clinic in Phoenix, AZ. Amy has been practicing physical therapy since 1988. She chose to specialize in vestibular physical therapy in 2003, completing the APTA competency course in 2006. She started working at the Banner Health concussion specialty clinic in August 2014, managing vestibular and balance disorders in the post injury population. In vestibular physical therapy, Amy’s interest is in assessing athletes in ways that more closely approximate sport related activity. Through her work with MMA fighters, Amy was part of a multiple discipline team that developed a sport specific return to play protocol for combat sports. She was also a part of the clinical research project assessing normative gaze stability in elite baseball players. Sport specific exertion and gaze stability is a current project that has evolved from working with athletes experiencing post-concussion syndrome.
Bridgett Wallace, PT, DPT
Bridgett Wallace, PT, DPT, has a doctorate of physical therapy and holds competency-based certifications in vestibular rehabilitation and concussion management. Dr. Wallace has been treating patients with dizziness and balance disorders for more than 20 years and is the founder and President of 360 Balance & Dizziness – a specialty clinic for the evaluation and treatment of dizziness and balance disorders that includes both audiology and therapy services. She is also the co-founder and Director of Clinical Education for 360 Neuro Health Institute, which provides online, mobile and live educational offerings for health care providers.
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