This live webinar is the first in a three part series that covers the importance of binocular vision at near and the tests used to assess the function of accommodation and vergence. In addition to step-by-step instructions on how on preform binocular vision tests, lecture notes include normal findings, what each test result indicates and useful clinical pearls for preforming these tests.
DR GAISER: Hello, everyone. My name is Dr. Hilary Gaiser. I’m an optometrist and assistant professor of optometry at the New England College of Optometry, and I practice here in Boston at the Charles River Community Health Center. So today I’m going to be doing the first part in a series of three lectures on binocular vision testing. First, before I get started, I just want to say thank you to the Orbis team for the opportunity to present today and to Dr. Sarah Wassnig and Dr. Catherine Johnstone for assisting me with the lecture today. So I said today is part one in a series of three lectures. Today I’ll be covering introductions to tests used to assess the function of accommodation and vergence and analysis of normative data and the test results. Part two is going to be an introduction to common near binocular vision disorders, how to identify these disorders using common binocular vision testing, and I’ll also be discussing cases and giving examples of common binocular vision disorders. In part three of my lectures, I’m going to be doing an introduction to common techniques to manage common binocular vision disorders. So today’s lecture objectives: I’m gonna teach you how to do an introductory battery of binocular vision testing procedures, and we’re gonna gain an introductory understanding of the theory of each binocular vision test. At the end of this lecture, I want you to be able to confidently conduct a basic binocular vision exam. So I’m just going to ask the audience: How familiar are you as a provider with completing a basic binocular vision assessment? Do you perform these regularly? Have you learned them, but you’re not confident in applying them? Have you seen them but never actually learned them, or do you have no knowledge of binocular vision tests? So I see a large majority of you are fairly — use basic binocular vision testing quite frequently, with some not so familiar. So that’s great. I hope this lecture is very helpful for you today. So what is functional binocular vision? The whole goal of having a good functioning binocular vision system is to have clear, comfortable, single vision using both your eyes. This is determined by a balance between the patient’s refraction, position, vergence ability, and accommodation. Any imbalance in these systems can negatively impact a patient’s quality of life. If there is an imbalance — maybe convergent insufficiency, the patient may not be able to pursue higher education or may have trouble reading. Things like that. So what are indications for binocular vision testing? So any abnormalities may be noted on binocular vision screening procedures. During a standard comprehensive exam, for example, cover test or stereovision. Maybe the patient is symptomatic for visual fatigue, headache, they’re having symptoms such as fluctuating vision or difficulty focusing, maybe some intermittent double vision. All these are indications for binocular vision testing. Binocular vision abnormalities are very common, and can affect all ages. They’re considered non-pathological. They’re considered an anomaly, in that they’re non-sight threatening, but they can significantly impact patients’ quality of life. I touched on this briefly, just a few seconds ago, but quality of life concerns include school, work performance, hobbies, and general visual discomfort. So when I’m thinking about a core binocular vision exam, a very basic introductory binocular vision exam, what do we need to be looking at? So the very first step is to determine the need based on case history or possibly a previous diagnosis and we must always, always start out with an accurate and current max full plus refraction with binocular balance. We don’t want to do a binocular vision exam on someone who simply might need a pair of glasses and might be symptomatic because they need a pair of glasses. We should always measure the magnitude and direction of any phorias, rule out any tropias at distance and near, and look at the AC/A ratio, which I’ll cover in more depth later. We should also assess the positive and negative fusional vergence using both direct and we can also use indirect methods. I’m just going to be covering the direct methods today. We should also be able to assess the convergence and accommodative amplitudes. And ideally evaluate sensory status and any potential suppression. So today I’m going to be going through and teaching you how to do the cover test, to look at a phoria or a tropia. And doing vergence testing, using step vergence with prism bars, and also the near point of convergence. Also we’ll be looking at accommodative amplitude, testing accommodation. And looking at something called AC/A ratio, or the accommodative convergence to accommodation ratio. We’ll also be looking at sensory status and suppression and testing this with a stereo vision test. And again, I can’t stress this enough: You must always start out with an accurate and up to date refraction. So just a word of caution before you start doing your binocular vision workup. Just be careful to take a full patient history. To rule out any possible pathology from something that’s more functional in nature. So, for example, any headaches that don’t correlate with binocular vision anomalies. Maybe the patient’s waking up with intense headaches, having nausea or vomiting. These don’t make sense with the headaches that occur more as a result of reading all day. That might be more linked with, say, something called convergence insufficiency. Just always be careful to take a full patient history. Also I highly recommend you complete a dilated ocular health assessment first, just to be on the safe side. Usually we’ll do some more basic binocular vision tests. Maybe we’re thinking there’s an issue. They have a full comprehensive dilated eye exam, and then come back for more binocular vision testing if needed. And again, always an updated and accurate glasses prescription. So I’m gonna be going into our first topic of the day. Cover test. I’m gonna be teaching you the cover/uncover and alternating cover test, to rule out a phoria versus a tropia, and get a better understanding of the patient’s eye alignment. So what are phorias and tropias? A phoria is the position of the eyes when binocularity is dissociated. This is sometimes referred to as the eyes’ resting position. Dissociation eliminates fusional vergence for the patient. You can do this in a couple different ways. Either occlusion or prism. And this essentially dissociates the eyes by presenting images that are unfusible, and then the eyes go to that resting position. In contrast, a tropia is a misalignment of the eyes when a fusible image is presented. So a patient should be able to fuse this image, but for whatever reason, they are not. A word of caution or of note: Since binocularity is impaired in patients with strabismus or a tropia, you often cannot perform binocular vision testing, because the patients are not binocular. So just always remember that if you’re doing your cover/uncover tests. Finding a tropia — probably won’t be able to measure vergences or use the testing I’m going to present today. With that said, there’s a caveat. It’s important to remember that tropias can be variable by the time of day, length of testing, and near work. So with careful case history, if it’s a more intermittent tropia, you might be able to perform some binocular vision testing. You may not. So cover test procedure. The purpose of this test is to determine if a patient has a phoria or a tropia. And the characteristics of that tropia when present. It’s objective, can be performed quickly and easily on most patients, is done in most exams, and can be used to measure the AC/A ratio. And I’ll go into more depth on that later. So one of the crucial components of the cover test is controlling accommodation. We need to select a proper target. So accommodation affects vergence, which then affects eye alignment. So there’s that near triad of pupil size, convergence, and accommodation. So the eyes converge, accommodate, and our pupils become smaller. All those three things are linked. So to control accommodation during the cover test, we need to choose a properly sized target, have the patient attend to that target, and keep it clear. It’s just very important when you’re performing this test to stress that you keep it clear. You might have them keep reading the next letter, if they’re doing this test at near. For children, there’s often lots of little targets where they can see little animals, and you can ask a question like: What color is the chicken? What color is the alligator? And things like that. The reason we want to do this is because that can change — under or overaccommodation can change the phoria position. For example, underaccommodation will overestimate an exophoria, and overaccommodation will underestimate an exo. So it’s important to keep stressing: Can you see the target? And keep it clear. So what targets — what are our options for targets? So for distance and near target cover testing, we use that accommodative target. We’re gonna select a target around 20/30, for a patient that’s 20/20. That’s usually one to two lines above the best corrected visual acuity in the poorer seeing eye. So if your poorer seeing eye is, say, seeing 20/40, we’re gonna have to select a target that’s more 20/50, 20/60. It’s ideal to keep the fixation target isolated, particularly at distance. This is a great distance target here. We’re isolating the E. We, again, need to always stress that the patient keeps the target clear. Here are some near sticks here at the bottom. There’s more pictures that you can use in children. I also have an example here that you can use, with the different letters and the different target size. So you might have them focus on one letter there at the bottom, when you’re performing this. You can also have them read the rest of the letters, ensuring that they’re keeping the target clear. So how do we set up this test? The patient is going to wear their habitual correction for the distance testing. So their distance glasses — if they take those glasses off when they’re reading, that’s how you want to test them. Or if they wear glasses full-time, you want to have them wear their glasses all the time. You’re gonna be eye level with the patient and behind the target as much as possible for near testing. So it’s ideal if you’re doing this test or right behind that you’re watching the patient’s eyes. For the distance target, you don’t want to get in the way of the target, so you need to be off to the side. But still as straight as possible. And we always need to have good lighting to maximize contrast on the target. And to pick up any small ocular movements. So first step is the cover/uncover test. The whole purpose of this test is to determine which eye is fixating. So how do we perform this test? I’m having my patient look at a target. I’m gonna pretend they’re gonna look at a target in the distance. You’re gonna cover the right eye with the paddle, pausing for three seconds, one, two, three, you’re gonna uncover and watch the eye move to fixate. Again, one, two, three. We’re gonna repeat that procedure twice, before switching to the left eye. If neither eye moves on that cover/uncover test, we’re gonna proceed to the alternate uncover test. So some examples here on the diagram: So we have our patient here, just looking at the patient. They look like they might have an eye that’s a little in here on the left. An eye that’s a little out here on the right. On the left as well here at the bottom. And this is more of an esotropia. This is an exotropia. And we go to do cover test. So we’re covering the right eye. When we cover the right eye, we notice that there’s movement out. Of that left eye. So that eye was in. It’s moving out. So that means that eye was an esotropia. Here at the bottom, we’re covering the right eye. When we cover that right eye, this eye that was out previously is now moving in to fixate. So that means it was out, moving in to fixate, it’s an exotropia. Here at the bottom we have a patient that looks a little bit more ortho to start with. We’re covering the left eye here. And whenever we uncover that eye, the eye moves out, and so that means the eye was in. And here on the bottom is just the reverse. We’re covering the eye. When we uncover it, the eye is moving in. That means that eye was out, previously. This takes quite a bit of practice. Just watch which eye is moving out. If neither eye moves, that means both eyes are fixating on the cover/uncover test, and the patient does not have a tropia, and we’re going to move to the alternating cover test. So on the alternating cover test, what we’re going to do is we’re going to move the occluder quickly between the two eyes, while keeping each eye individually covered for three seconds. This is gonna keep the eyes dissociated, disrupt that fusional vergence, and allow the eyes to go to their phoria positions. So it’s gonna be one, two, three. One, two, three. One, two, three. And we’re gonna watch for any eye movement. So the eyelid is not occluded. It’s gonna fixate on the target, while the other eye will go to its phoria position. So we have two eyes straight ahead. Covering the left eye, you can see behind this little magic occluder here that the eye is a little bit in. And we move that occluder over to the right eye. This eye right here is moving out a little bit, so that means it’s in, it’s moving out, we’re covering this eye — we can see again behind my magic occluder that this is in. When we move it over to the left eye, that eye goes out again. This eye is in again. So essentially, when we’re covering it, the eye is in. That’s its resting position, because it’s dissociated. And the eye flicks out when it’s uncovered. So they’re flicking in, they’re working together, in phorias — both eyes are moving together — and this is an example of an esophoria. So thinking about cover analysis, if an eye moves to fixate during the cover/uncover test, then that patient has a tropia. For tropias, we need four different components. We need the laterality, left, right, or alternating. If it’s always on the right eye, always on the left eye, do you see the eye moving out on the left or the right? That’s more of an alternating laterality. We also need to know the frequency. Is the tropia always there, or is it intermittent? Also we need to know the magnitude, which you can do by two methods. You can neutralize with prism bars or loose prism lenses, and when you get more experience, you can also learn how to estimate the magnitude. We also need to know the direction. Is it hyper, hypo, is it exo, or is it eso? So if the eyes do not move during cover/uncover, but do with the alternating cover test, that means we’re dealing with a phoria, and we only need two components when we’re recording and looking at a phoria. We need the magnitude and the direction. So I’m going to show you a video on the cover test procedure. And I’m going to talk you through this. So again, your patient is wearing the habitual correction. A good accommodative target, one to two lines larger than the patient’s worst VA. You can also use your hand as an occluder if the patient’s a child. Here’s our target. We’re going to perform the cover/uncover test first. There’s our patient. We’re doing this test at distance first. So cover, uncover. No movement is noted. And again, we’re switching to the left eye. Cover, uncover. At distance, no movement is noted. So now, because we didn’t see any movement on the cover/uncover test, we’re going to go to the alternating cover test. So cover one, two, three. Cover, one, two, three. This is the alternating cover test at distance. Again, no movements noted. Oh, maybe a slight movement there. So very slight exophoria at distance. So we’re going to be doing similar procedure, but at near now. So again, we’re gonna use an accommodative target at 40 centimeters, with good illumination on the target. We’re gonna be doing the cover/uncover test first. And we see how the eye… Is moving in. That means it was out behind the occluder. We’re gonna do this on the left eye now. And also note how that eye is moving in, which means it was out behind the occluder. And this means that the patient has a tropia. So they have an exotropia. That is alternating, because you see it in both the left and the right eyes. Cover/uncover test again. That eye is moving in. Now going to be doing alternating. And each eye is moving in on alternating. That means the eye is out behind the occluder. So she has a moderate to large exophoria. No we’re going to be doing the test with the patient’s habitual correction. And if we note on the cover/uncover test, there is now no movement of that right eye. And again, we’re doing the cover/uncover test on the left eye. And there is no movement with habitual correction. And on alternating cover test… Again, there’s no movement with the patient’s habitual correction. So this patient has an alternating exotropia, uncorrected, which is corrected when they’re wearing their appropriate glasses prescription. So when we’re doing cover test, we want to know the magnitude of the phoria or tropia. And we’re going to neutralize this with prism. An easy way to think about this, how to measure it: The base is where the eye moves towards, and the apex points to where the eye is in a phoria position. And we’re no longer gonna see movement on the alternating cover test when the deviation is neutralized. So say I have an exo. I’m gonna hold my base in. I would alternate and keep moving up. Until I no longer saw any movement. We can also do this with the cover/uncover test. To neutralize the phoria or tropia. Prism bars have base in, or horizontal, and we also have prism bars with base up for vertical deviations. So I encourage you to practice. You can also use loose prism lenses. So amount of prism when there’s no longer movement is gonna equal the magnitude of the deviation. And just interpreting movement or thinking about movement, if the eye moves in to fixate, that means the eye was out, either phoria or tropia. That’s an exo. We’re gonna measure that with base in. If the eye moves out to fixate, that means the eye was in. We use base out. If the eye moves down to fixate, that means the eye was up or hyper. If, for example, this is in the right eye, we’re gonna use a base down in the right eye to measure. On the opposite side, if the eye is moving up to fixate, that means the eye was down. For right eye, we would measure with base up in the right eye. I just want to ask you a question: On cover test you note that on the cover/uncover portion of the test the patient’s left eye always moves in to fixate when the right eye is covered. When the cover/uncover test is performed on the left eye, the right eye does not move in to fixate. How would you describe the patient’s findings? Good. Majority got that it was a constant left exotropia. So it’s constant. It’s always there. But it’s a tropia, because we’re doing the cover/uncover portion. It’s not an exophoria. It’s an exotropia. Great job. So when we’re thinking about the normative data in recording of cover tests, what is normal? So a distance anywhere between 1 prism diopters esophoria to 3 prism diopters exophoria is normal. Near, orthophoria to 6 prism diopters exophoria. Tropias are never normal. SC is an abbreviation for with prescription and CC is with prescription. And you also need to know with which prescription you’re testing. Are you testing with habitual or a new updated prescription for today? You need the test distance, whether it’s at distance or near, the direction and magnitude, if it’s a phoria. For tropias, we’re going to add in laterality and frequency. So for example, we have here a cover test with glasses at 40 centimeters, and we found approximately a 4 prism diopter of esophoria. This is just an abbreviation for esophoria. It’s perfectly fine to write it out as well. For a second example, cover test without correction at distance. We have a 5 prism diopter exotropia, abbreviated XT. Just to note: Usually the little tilde here is used for approximate. That means we just observed it and estimated it. Where the little delta stands for being measured. You can also write estimated or measured. That’s also correct. What are some troubleshooting? If we’re running into problems with cover tests? Sometimes we have to repeat, if the patient is symptomatic, but we’re not really seeing anything, say. They have the complaint: Oh, little Johnny — their eye turns in the evening. You’re doing the exam, but you’re not really seeing anything. You might have to repeat that multiple times. You might even have the patient come back at the end of the day, or we might repeat it at the end of the exam, if the large phoria is noted at the beginning, because it might break down into a tropia. Maybe it’s more intermittent in nature. If the patient has good control most of the time, but upon fatigue, that phoria breaks down into a tropia. And again, I mentioned this before: But you can also have the patient read letters to ensure that they are indeed keeping the target clear. We’re gonna move into vergence testing. And cover two techniques. Near point of convergence, or NPC, and step vergences. What is vergence? Eye alignment that depends on the balance between fusional vergence and the patient’s phoria — essentially we’re thinking of supply and demand. We have a phoria, that’s the demand. We have vergence, which is the supply. Vergence is the movement of the visual axis towards or away from each other, in order to keep images single. So convergence is towards each other. Divergence is away from each other. Hypervergence of one eye, and hypovergence of the other eye. The eyes work like this and they work like this. There are two types of vergence that I’m going to discuss today. Fusional is stimulated by retinal disparity. And accommodative is stimulated by that accommodation reflex. And remember, our near triad or synkinetic triad of convergence, accommodation, and pupillary response. Here’s an example of convergence. Here’s an example of divergence. So what do I mean when I’m talking about vergence supply and demand? Again, demand is exo. My eyes are out. I’m gonna have to use compensating convergence or positive fusional vergence to bring my eyes in, to keep them aligned. What about if my natural position of my eye is eso? Esophoria, for example? I’m gonna need compensating divergence or negative fusional vergence to keep my eyes aligned. In right hyper, I’m gonna need right hypovergence, and if I have a right hypo, I’m gonna need right hypervergence to keep my eyes aligned. So in context, what can happen? So a patient has no motor fusion, not able to use their vergence. They’re gonna have a constant strabismus. My patient has intermittent motor fusion. They’re gonna have more of an intermittent strabismus. Or potentially a decompensating phoria. Maybe my patient has motor fusion, but there’s difficulty or discomfort maintaining it. So they can compensate for that phoria, but it’s difficult and they’re symptomatic. I’ll call this a symptomatic phoria. What if the patient has comfortable motor fusion, and if the patient has comfortable motor fusion, we typically assume that they’re gonna have a normal phoria. So the first test I’m going to cover, with the vergence testing, is near point of convergence, or NPC. The purpose of this test is to assess the absolute convergence limit. This is important in diagnosing a very common binocular vision disorder called convergence insufficiency. This is both an objective and subjective test. So the setup for NPC is shown in this picture below. The patient needs to use their habitual correction, or the prescription through which you would like more information about the absolute convergence limit. So you found a large change in prescription. Maybe 1 to 2 diopters. You want to make sure that patient’s going to be comfortable. So maybe you put that in a trial frame and test your NPC again through it. We have different targets we can use. We can use our accommodative target, like we did in cover test. We can use a light or non-accommodative target. This is good for presbyopes. We can also use a red lens to add an additional barrier to fusion, and use the light as well to perform this test. All three are perfectly fine methods to use. So the NPC procedure — so you’re going to move the target towards the bridge of the patient’s nose, and ask the patient to tell you when the target appears double. You’re gonna observe the patient’s eyes for any loss of binocular fixation. This is known as the break point. If the patient reports double vision or diplopia at any time, this is known as the break point. And we should observe and record the eye that loses fixation in either case. So once the target becomes double, or an eye loses fixation, then you’re going to move the target away from the patient again, and ask them to tell you when the target becomes single again. You’re gonna record this as the recovery point. If the patient does not report diplopia at any point, but you as the provider note that an eye loses fixation, then they are likely suppressing, and you’re gonna have to record the eye that’s out, and that they’re suppressing. So make sure you measure the break and recovery point with a ruler. You can estimate as you gain experience, but it’s good to use — a lot of the near cards have a little ruler on them that you can use. So I’m gonna show you a video of just the NPC procedure. So bringing the light target in. At some point, we’re gonna note that that left eye is gonna — oop, there it is. It broke. And then bring it back until she recovers. And you would record — measure and record the distance, and which eye went out. So when we’re recording, we need to record the tests used. So NPC. And the type of stimulus used. Did we use an accommodative target, a light target, or red lens? We need to know with or without correction. And with correction, which prescription. And we need to record the break and recovery. You can use centimeters or inches. Diplopia per patient report — that’s the more subjective portion of the exam. Or suppression, if the patient lost binocular fixation, but did not report diplopia. We also need to know which eye lost fixation. So here are some examples of recording. Near cover, near point of convergence, with correction, accommodative target, break was 6, recovery was 10, diplopia was noted, and the right eye was out. Again, on the bottom here, second example: Near point of convergence, corrected, with a light target, break was 8, recovery was 12, suppression was noted in this case. And the left eye was out. So thinking about near point of convergence in context, what can happen? What are our different outcomes? So first case: The patient maintains binocular fixation. Never reports diplopia. You don’t see the eye out. The patient can follow the target to the bridge of the nose. We record this as TTN or to the nose. No break point is noted. Second scenario is: The patient reports diplopia, and you observe the eyes lose binocular fixation, so your observation should match the patient’s report. And again, that break point is when the patient reported double, and you saw them lose fixation. And then the recovery point would be when they would report single, and you would observe that they have gained fixation. What happens in our third scenario here? You observe that the eyes lose binocular fixation, but the patient does not report diplopia. This means that the patient is potentially suppressing the deviated eye, or they might not understand the test. This is very common in younger children. Again, we need to record the break point or when the patient lost binocular fixation. Sometimes we’re gonna use this test in more of an objective method. We’re just gonna record the eye is out. This is often all that we have for children. So what of our norms? So for an accommodative target, break and recovery. Break is around 5 centimeters and recovery is 7. This is the least receded near point of convergence, because it engages both accommodative and fusional vergence. For pen light target or light target, a little bit more receded, because we’re not using — it’s a non-accommodative target. We’re not using our accommodative system to help us with our convergence. Break is under 7 centimeters, recovery under 10. If we repeat this test with a red lens, this might suggest an even more significant convergence problem. And we see more recession. Any failure of the patient to report diplopia as the eye turns out indicates suppression. Some troubleshooting that we can do. If NPC is more receded, we’re gonna think the patient potentially has convergence insufficiency, and we would need to evaluate more. What happens if the patient has symptoms, they’re coming in with complaints like fluctuating, blurry vision at near, maybe eye turn, things like that, but you’re finding a normal initial near point of convergence, and you’re like… What’s going on? So we might have to repeat this test multiple times. Five times is recommended to assess for any fatigue. We can also repeat this test at maybe the end of the exam as well. Or we can repeat again with that red lens. Red lens on the right eye, using that light source. To add another barrier, and you might find that NPC is more receded. So I’m going to ask you another question. So you were performing near point of convergence on a 6-year-old child. And you know that the right eye loses fixation around 4 centimeters, and recovers at 7. The child does not report that the target has doubled, however. What is the most likely assessment of the patient’s findings? So I tricked you a little bit on this. Number one, totally correct. But number four is also really likely. It’s a 6-year-old child, so maybe they don’t understand the test. So we’re not able to 100% definitively determine suppression or diplopia. So we’re gonna rely on objective findings. However, if this 6-year-old child was now a 16-year-old, 100% number one would be the correct answer. Not necessarily wrong, but just think about the patient you’re working with, and when this test might be — you might need to use this test a little bit more objectively. So I’m now gonna go into vergence testing, using the step method with your prism bars. So this technique measures your fusional vergence. We’re gonna introduce prism under binocular conditions to test the patient’s fusional vergence ability. The prism is gonna create retinal image disparity. It’s gonna move those images away from the fovea of each eye and is gonna stimulate our fusional vergence. So your patient is going to… We’re gonna introduce prism. And the patient is gonna move their eyes until their supply of vergence innervation is depleted. Because accommodation and vergence are linked, the patient is first gonna use up their supply of accommodation convergence. They’re gonna report blur, and then they’ll use up the rest of their fusional vergence and report double. So we do both base in and base out. You can use base up and base down as well. I’m just gonna cover lateral vergence testing in this lecture today. So we’re using base in. Base in, light is gonna deviate to the base, the prism images are gonna move nasally on the retinas, and the patient is going to need to diverge to keep the image on the fovea. When the patient’s diverging, this is going to test negative fusional vergence. In base out, exactly the opposite. Base out, the image is gonna move temporally on the retinas. The patient is going to converge to keep the image on the fovea. And this tests your positive fusional vergence ability. So when testing vergences, an easy way to think about it is that the corneas are gonna move towards the apex of the prism. So the purpose of step vergences is to measure a patient’s ability to maintain clear and single binocular vision, while changing vergence and holding accommodation constant. Again, I can’t stress the importance of this enough: We’re going to use an accommodative target at a constant viewing distance. This is a free space technique, so we’re only going to be using prism over one eye. There is a technique that you can do in the phoropter called smooth vergences, where you put in prism equally before each eye and add the two prism distances together, but we’re just gonna do the free space technique today. This is an objective and a subjective test. It’s subjective because you’re asking the patient to report when the target becomes double, and you’re also observing for the patient to lose fixation. Just a caveat: A patient must be able to fuse in order to measure fusional vergences, so you can’t do this on any patients that are exhibiting a tropia. So how do we perform this technique? Again, we need habitual correction, or the correction through which you want vergence information. We can test both at distance and near. We need to use an appropriate near and distance target, an isolated line or letter, one to two lines above the best corrected in the worst seeing eye. We’re gonna place the prism bar base in before the one eye, and move it step by step as the patient looks to the target. And you’re going to ask the patient to report when the target becomes blurry, breaks into two, and comes back into one. So if the patient — maybe you’re working with a young child, for example — if the patient fails to report blur, break, or recovery, you’re gonna watch for the patient’s eye to flick off the target and you’re gonna record that as your break point. When the eyes return to their initial position, that’s going to be recovery. So we’re going to repeat. We’ve done base in first. We’re gonna repeat doing base out prism. We always report base in before base out, because we want to avoid any potential prism adaptation. So I’m gonna show you a video. Of the step vergence technique. So she’s moving the prism. She’s attending to the target. At some point, that eye is going to flick. Oh, so it’s flicked there. One more. Yeah, not maintaining fixation. So she’s gonna go back. And then she has maintained — resumed fixation. So you would record the amount of base in prism, for example, when you note the break, and then the prism number when they resume fixation. What are our values? We don’t have normative values for blur. This is adapted from Scheiman and Wick. But we have normative values for break and recovery. Something I will touch on today, but I’ll cover more in depth on in part two of my binocular vision lecture is Sheard’s criteria. So Sheard’s criteria says the patient is likely to not be symptomatic if they have at least twice the compensating fusional vergence, twice their phoria’s worth of compensating fusional vergence. So say I have a phoria of 10XO. As long as I have at least — 6XO — as long as I have enough compensating fusional vergence of 12, I should be okay. Again, I just want to introduce this topic now. I cover this more in depth in part two of my lecture. So just a little bit more advanced question. But I still wanted to ask it. On positive vergence testing, base out, you record the following findings: So you find on base out that there’s no blur. There’s a break at 15 and recovery on 7. On cover test, you find the patient has a 5 prism diopter exophoria. Do you expect this patient to be symptomatic? Excellent. So no, we don’t expect them to be symptomatic. Number two, because they have 5, they have 15 positive fusional vergence. I’m gonna go next into a clinical test of accommodation. I’m only gonna be covering amps today. What are our indications for testing accommodation? Any reduced near visual acuity, especially in a non-presbyope, or any symptoms that suggest a potential accommodative anomaly. Such as blurred vision, fluctuating near vision, increased distance blur after reading, headache or eye strain after near work, any fluctuating vision not associated with a health risk factor such as dry eye. This is why I can’t stress the importance enough of doing a full complete dilated ocular exam before we do a binocular vision workup. Also I just want to touch base on pseudomyopia. Again, I cover more binocular vision anomalies in part two of my lectures, but I’m introducing this topic now. Pseudomyopia is any visual acuity that suggests more minus than ret refraction. Say they’re reading 20/20, but you’re noticing -1 or -2. It doesn’t really correlate those two findings. We think there might be pseudomyopia, might be an accommodative issue, and we would need to follow up with that. So there’s lots of different categories of accommodation testing. I’m gonna cover amplitude of accommodation, because it’s really quick, easy to do, more screening, doesn’t require any specialized equipment, other than the target that you’re also using for near point of convergence and cover test. So that’s the entire amplitude of accommodation. We can also look at relative accommodation using a technique called NRA/PRA. This is done in the phoropter. And there’s also using MEM, which is with the retinoscope, and binocular cross cylinder in the phoropter, and also can look at accommodative facility and the speed of accommodation. I will cover the one that’s underlined, and I will also be looking at the link between accommodation and vergence. This is really more of a vergence test. I’m just listing it here. So amplitude of accommodation testing. We’re gonna be using the push-up method. The purpose is to measure, in diopters, the patient’s ability to change focus and respond to near stimulus. This is subjective and a monocular technique. The patient is gonna wear their habitual near prescription or the prescription through which you want more information. You must always record through which prescription we’re testing. The target needs to be well illuminated row of letters, one or two lines larger than the near visual acuity. We’re going to test each eye separately. We’re going to ask the patient to report when the letters first become and stay blurry. This is very, very important. It first needs to become blurry and stay blurry. We need to measure the distance from the card to the spectacle plane in centimeters, and convert to diopters. So say we measure 10 centimeters. That converts to 10 diopters. This is just the recording we’re gonna use. We need the test used, with or without correction, and which prescription through which we’re testing. We’re going to record AMPS in diopters. We do not record AMPS in centimeters. We need the right eye and left eye separately. So, for example, Amp, push-up method. With correction, we found 7 in both the left and the right eyes. What are the norms and what are we thinking about when we’re analyzing this information? A good rule to follow is something called the one half amp in reserve. This means we expect sustained clear and comfortable single vision when a patient is only using half of their amps during near work. Before we measure amps, just a word of caution, we need to evaluate and correct for any undercorrected hyperopia, overcorrected myopia or presbyopia. That can always affect our amplitude findings, and after we’ve ruled out these things, then we can consider evaluating for an accommodative anomaly. Hofstetter’s formula is a good rule to follow. It gives us average amps to expect and minimum to expect, based on the patient’s age. We typically use minimum when comparing the findings to the expected amps. This is 15 minus a quarter of the patient’s age in years, and we’re gonna expect the patient is going to be comfortable when they have at least twice that… Or half that amp in reserve. So they need to have at least 5 diopters of accommodative amplitude in order to likely function comfortably. I’m just gonna show you — this doesn’t have any audio. I’m going to speak through it. So they’re measuring near visual acuity. They’ve measured the target. She’s gonna have the patient focus on a line of letters that’s one to two lines above her best corrected VA. Going to bring the card slowly towards the patient’s eyes, and the patient is going to report their first sustained blur. Patient reported blur. Going to measure from the spectacle plane to the card and convert that to diopters. So that was for the right eye. The procedure gets repeated the same way for the left eye. So now we’ve measured, we’ve looked at our vergences. We’ve looked at our accommodation. One technique to measure accommodation. Now we’re gonna look at the AC/A ratio linking accommodation and vergence. What is the AC/A ratio? It uses the concepts of blur and convergence accommodation. Blur reflex is gonna be small changes in accommodation in response to detection of blur, and blur is stimulated by changes in fusional vergence. So increasing accommodation is gonna increase your positive fusional vergence and decreasing accommodation is gonna decrease your positive fusional vergence. So the purpose of this is to determine the change in accommodative convergence when the patient increases accommodation by a given amount, so the fusional vergence stimulus stays constant. Plus lenses are gonna relax the accommodation, and reflexively, convergence is gonna decrease. Minus lenses is gonna stimulate accommodation and we expect convergence to increase. This is gonna make exos smaller and esos larger. What’s the procedure? We’re gonna remeasure the patient’s near lateral phoria, using +1 or -2 lenses. We can just use flippers. Over the patient’s habitual prescription. And we’re gonna use cover tests to do so. We can also do this test in the phoropter. We can measure this several different ways. The cover test is quick, easy, and portable. So when we’re doing this, with plus and minus 1, this is gonna force accommodation to change by 1 diopter. This is the A portion of the AC/A ratio. We’re gonna look at the differences between the two phoria measurements. This is gonna give the AC part of the AC/A ratio. You can also use plus and minus 2 flippers. You just need to convert this ratio to whatever you find out of 1. So say you come 8/2. Difference — that’s gonna be a 4/1. 4 to 1. So let’s look at an example. So in refraction, we found -2 in both the right and the left eyes. The phoria through the habitual, they found a 4 prism diopter exophoria. We remeasure the phoria through +1 flippers. Remember, this is gonna relax accommodation. Make exos larger. Found an 8 exophoria. We’re gonna remeasure the phoria through -1, and we find ortho. So again, we stimulated accommodation, stimulated convergence, and now we’re moving more eso. So this gives us an AC/A ratio of 4 to 1. So what are the norms for AC/A ratio? Normal is 4 to 1 to 6 to 1. Low is anything under 4 to 1, and high is anything greater than 6 to 1. Really consider, depending who you read, some people recommend using +1 all the time. I’ve read others. Some recommend using -1. But I think it’s really important to do both plus and minus 1, because you can get an understanding if there are issues noted in either direction. The ratio should be the same regardless, but maybe the patient has more difficulty relaxing accommodation, more difficulty with the plus side of things, or maybe they have problems stimulating accommodation, and then an unequal ratio in either direction can give you clues to what’s going on with the patient’s accommodative convergence system. So I’m gonna ask you a question here: So when measuring a patient’s near phoria using a cover test, you find a 6 prism diopter esophoria. And when we repeat the test using +2 flippers, we are now finding a 6 prism diopter exophoria. What is the patient’s AC/A ratio, and is it within norms? Great, so the answer is 6 to 1, because we need to reduce that ratio down. So 6 eso, 6 exo. Total difference of 12, we use +2, so that’s 12/2, but we write that as 6 to 1, and that is not within norms. That would represent a high AC/A ratio. So the last technique I’m gonna cover today is sensory status. There’s lots of different stereovision tests that we can use to measure sensory status. What is sensory fusion? It’s testing the ability of the eyes to combine sensory information such as form, color, illumination, location in space, from both the left and the right eyes into a single perception. So different information is being presented to each eye, following our eyes combining this information. So stereopsis is the true depth perception, true binocular perception of depth. Our eyes can also use monocular clues, but that’s not a true depth perception. Just gonna cover quickly monocular depth cues, so you have a better understanding of that. These are learned as a result of our interaction with the visual world. It’s used by everyone for distance over 200 meters. We use such things as internal cues, such as accommodation convergence, geometric perspective, light, and shadow, to help clue us into the depth. We’re gonna contrast that to normal stereopsis. So normal stereopsis is when we have two eyes that function normally and equally. There are similar retinal images in both the left and the right eye, and we’re gonna look at the motor fusion ability and how it interacts with sensory fusion to maintain bifoveal fixation on the eyes to turn both those images into a single image. So motor fusion and sensory fusion are linked. We need both, and any imbalance can lead to reduced stereopsis and binocularity. So I’ve gotten questions about the development of stereopsis. I wanted to touch base on this. So… Any patient — children that might have strabismus around this so-called critical period, around 7 years, give or take, they’re likely not to develop stereopsis normally, unless they’re caught and corrected. That’s why it’s really important that we’re doing this tests on younger individuals, all this binocular vision testing, because we want to pick it up and get them corrected so they can develop stereo normally. So in adults, once stereopsis has set in, if they’ve had previous normal stereo and they lose that stereo because of any strabismus, say, once that strabismus is corrected, because they had it previously, stereopsis is normally going to be restored. There is some new research related to neuroplasticity suggesting that the critical period may not fully be set in stone, and adults may lose stereopsis if strabismus lasts for two to three months, so keep up to date with research coming up, but this is generally the case. There are a variety of methods for testing. Polaroid filters are the most common, but there are also color filters. Some of the most common tests are Random Dot 2, Random Dot 3. Any of these are fine to use, as long as you look at the testing distance and the norms to use. So level of stereopsis is measured in the angular separation and the target in sections of arc. We also need to test with a habitual correction for near. We might need to use some testing glasses, such as Polaroid glasses over the patient’s glasses, and we need good overhead illumination with no glare. it’s recommended that the practitioner hold the book at eye level without moving so they can’t get any clues to stereo vision. We need to use the correct distance that the test is calibrated for. A longer distance can artificially mean finer levels of stereo. How to record stereopsis. We need the test used, with or without correction, type of stereo if applicable. Some tests have local and global, so you just need to record which one. The testing distance, and we record the measurement in seconds of arcs. Stereopsis norms are variable for patients’ age and type of test, but generally around 25 seconds of arc is considered good or normal. So just to summarize, we’ve learned a lot of different techniques today. I want you to be able to confidently complete testing for binocular vision exam. With cover test at both distance and near, to determine phorias versus tropias. Near point of convergence, so your vergence amplitude, and step prism bar is your vergences. Test of accommodation we covered at amplitude. And then we looked at the accommodative convergence, so accommodation ratio, or AC/A ratio. We also briefly touched base on sensory status using stereovision. So my next lecture is going to cover common binocular vision anomalies in patient cases, and my third lecture is gonna cover some treatment options for these conditions. Thank you! It was great speaking with you today. Some references. And do you have any questions for me today?>> Thank you, Dr. Gaiser. We have about six questions, if you want to stop your screen share and open it up. It should be up top.
DR GAISER: I’m not seeing it. Oh, there it is. So first question is: If the near target has a few lines of different size, how are you going to choose the target? So you’re gonna measure the near visual acuity, and you’re gonna select a target that’s 1 to 2 lines larger than the patient’s best corrected VA. So if they’re 20/20, you’re gonna choose maybe around 20/30, if they’re 20/30, you might choose a 20/40 target to 20/50. So you want to measure the near visual acuity first, and that’s gonna allow you to select proper targets. Okay. Then we had a question about monocular clues. I briefly touched on this in the stereopsis section. We don’t really test monocular cues. We’re gonna use the stereovision booklets to test true depth perception, rather than monocular clues. Good question. Next question. If the patient is presbyopic, how do we check phorias or tropias at near? Again, I can’t stress this enough: This is why we need a full, accurate maximum plus prescription, and the patient needs to be adequately corrected for near. So you would do this with their habitual near glasses on. So they should be wearing glasses that fully correct them for near. And then you are gonna retest the phoria. You’re gonna check the phoria when they’re fully corrected, so they should be able to see the target. And you’re gonna measure near visual acuity before you do the cover test findings. I had a question about tropias in adults, versus children. I’m gonna cover this more in lecture 3, when I talk about management. This is a good question. Next question is: Which eye should we present the prism in front of? I’m assuming we’re talking about measuring our vergences with the step prism. Because the eyes are yoked and work together, we can do either eye. We just always need to measure base in before base out. So we can do either eye. You’ll notice if you just want to do it in both, just to kind of learn, that the answer will be the same in both eyes. So we only put it in front of — it doesn’t matter which eye. By convention, I typically just use the right eye. Another good question: Is there any difference between measuring accommodation with letters and picture targets? Great question. So if we’re using picture targets, that’s not necessarily a great control of accommodation, but it’s appropriate usually for children. So you wouldn’t want to use picture targets, necessarily, for adults. You might want to use more of a tumbling E or a letter target. Picture targets — with children, we just need to get them to attend to the target and pay attention, so those are more appropriate, but it’s ideal to use letters. I’ve got a question using step fusional vergence or smooth fusional vergence. Step fusional vergence is with the prism bars in free space. Smooth fusional vergence is in the phoropter. I do prefer step fusional vergence, because it’s an objective and subjective test. Where smooth fusional vergence in the phoropter is only subjective. We’re relying only on the patient’s response. But with the prism, I’m able to see when my patient’s eyes lose fixation. So in a child, it’s particularly helpful — or someone that might not understand the explanation of the test or able to follow directions — I do prefer step fusional vergence, because I can see as the provider what is going on, and I’m not able to do so if the patient is behind the phoropter. I’m also getting a lot of questions about stereopsis and glaucoma. That’s a little outside of the scope of this lecture. I will try to cover this briefly in the management of binocular vision conditions. But a little outside of the lecture for today. Speaking about glaucoma. Are there any more questions?