Lecture: Assessment of Amblyopia – What to Look Out For?

More and more children are being diagnosed with Amblyopia earlier in life due to increased awareness, improved access to eye care, and school vision screening programs. This emphasizes the need for Optometrists as primary eye care practitioners to be equipped with the knowledge and skill set to be able to appropriately diagnose Amblyopia, manage and refer to Ophthalmologists in required cases.

This talk will focus on the clinical tests, interpretation, and systematic approach to assessing Amblyopia. The talk will also provide an outline to sequential management and vision therapy options.

Lecturer: Dr. Jameel Rizwana Hussaindeen, Sankara Nethralaya, Chennai, India


DR RIZWANA: Warm welcome. So over the next 45 minutes, I’m going to be speaking about assessment of amblyopia, what to look out for, so first I would begin with some warm acknowledgments to the team behind — not just this presentation, but the entire work that happens in the binocular vision clinic. So the first is to my entire team, and a specific mention to three people who helped in making this presentation and preparing the multimedia files. And Ms. Archayeeta Rakshit, who specifically helped a lot, when we were trying to establish the amblyopia clinic in Sankara Nethralaya. To the entire Cybersight team, Orbis India, a specific mention to Dr. Rishi, for really coordinating the entire show, and Mr. Ashweta. To all our patients and the pediatric ophthalmology department of SN. Because we work together with so much synergy that we are able to accomplish so much. And to all my mentors in the department. And especially a mention to my mentor Professor Mitchell Scheiman, who has taught so much in this area. And this is my beautiful team that is here. So this is the overview of today’s presentation. And this is the famous Hippocratic quote. I tried to find the authenticity of this quote, but unfortunately I couldn’t. But whatever it is, we all like this quote. So when the doctor sees nothing and the patient sees nothing, the diagnosis is amblyopia. So amblyopia still remains as a diagnosis of exclusion. And I would take time to really acknowledge these two people, who contributed a lot in the understanding of neurophysiology of amblyopia especially. In the very early years. In the 1960s, at the Harvard Medical School, that David Hubel and Torsten Wiesel, in the department of neurobiology. They tried to understand the development of ocular dominance columns, and how the vision develops in an immature brain, and what are the effects of occlusion or patching, and so they used kittens and single cell recordings were done, as early as the 1960s, to understand this. And they of course got a Nobel Prize for their expert opinion in this area. So a lot of our current understanding draws back from the work done by David Hubel and Torsten Wiesel. So amblyopia is derived from two Greek words, amblyo, meaning dull, and opia, meaning vision. So amblyopia, meaning dullness of vision. And the famous definition given by Professor Noorden that we keep studying from the very beginning in optometry and ophthalmology, is decrease of visual acuity caused by abnormal binocular interaction that can occur in one or both eyes, and there are some of — there are important components to this definition. Number one is: Any deprivation should happen within the critical period, and there should not be any specific cause that is detected during the eye examination. And when we detect this early, we should be able to reverse it by appropriate therapeutic measures. So basically any abnormal — any visual impairment due to abnormal visual development in early life is a potential risk factor for amblyopia. But there are also other risk factors that are mentioned here. Including preterm birth, low birth weight, ROP, cerebral palsy, any developmental delay, family history of amblyopia, any organic pathologies, and maternal factors such as smoking, antihistamine ingestion, and alcohol. But amblyopia can be present even in the absence of these risk factors. From a functional perspective, beyond visual acuity, if we want to characterize amblyopia, this is one of my favorite definitions that Dr. Lisa Asper has given in her paper, where she defines amblyopia as a visual cacophony of deficits, not just limited to visual acuity, but in contrast sensitivity, spatial localization, fixation, ocular motility, accommodation, crowding, attention, motion perception, and temporal processing. Now, why do we have to understand amblyopia in so much detail is because the testing that we would do when a patient with amblyopia comes to us and the appropriate therapy or treatment modalities that we want to cater to, depending upon the deficits that we identify in these areas, definitely we need to have an understanding of what really happens in amblyopia, beyond visual acuity. So the preferred practice pattern guidelines by the American Academy of Ophthalmology proposes these diagnostic criteria for amblyopia, as you would see here, which is: In case of unilateral amblyopia, if there is an objection to monocular occlusion, or if there is a specific fixation preference, and if there is an interocular difference of two or more octaves, so basically if we are dealing with preverbal kids, we would be using preferential looking, just like the Teller acuity cards, or the Cardiff test. And if a child shows a difference of more than four card difference between the two eyes, then that means, you know, there’s a two octave difference. So if we see an interocular difference of two or more octaves, or an interocular acuity difference of two or more lines, best corrected visual acuity, then that is suggestive of unilateral amblyopia. When it comes to best corrected visual acuity, of course we need to have age-corrected norms. So as you would see here, there are different norms that are proposed for different age groups, beginning from 3 to more than 5. So you would use the criteria of 6 by 9 or 20 by 30, only when the child crosses the age of 5. And depending on etiology, you can classify amblyopia as follows. The first being strabismic, which is of course when the strabismus is constant and it’s not alternating. The second being refractive, so the three classifications to this: Number one being the difference in refractive error between the two eyes, by more than 1.5 diopters, or an astigmatic component, which is represented by meridional amblyopia, or a bilateral high refractive error, which is termed as isoametropic amblyopia. The third is visual deprivation due to any kind of organic pathologies, including media opacity, such as congenital cataract, or lenticular opacities, or even a congenital ptosis. The last one is occlusion amblyopia, where in the process of occlusion for amblyopia treatment, the good eye or the better eye develops amblyopia. And if there are more than one etiology to amblyopia, then we would call it a combined mechanism amblyopia. So that is based on etiology. So far, we did see the visual acuity criteria. We did see about the etiology-based classification. Now, based on severity of visual acuity, PEDIG has proposed this particular classification. So earlier we used to call this as shallow, moderate, or deep amblyopia. But then it is preferred to be called as mild, moderate, and severe. So the 20 by 25 — the 20 cutoffs have been converted to 6 by, because of the systems that we follow here. So as you would see here, these are the different visual acuity levels that you need to be using, when you want to classify amblyopia based on the visual acuity. Now, when we want to prescribe for amblyopia especially, definitely we need to be aware of the refractive correction guidelines. This is, again, the guidelines given by the American Academy of Ophthalmology, based on the consensus that they arrived at. And as you would see here, again, these are age-based guidelines for myopia, hyperopia, hyperopia with esotropia, and astigmatism, and whenever there is an anisometropia, definitely the thresholds are much more lower, which means that even if the refractive error is lesser, you would go ahead and prescribe, because the child has an added risk of now anisometropia coming into the picture. Now, when there is an additional strabismic component, especially when there is hyperopia, there is generally no — you don’t look at cutoffs. You would go ahead and prescribe the full cycloplegic correction in such cases. So these can serve as useful references to optometrists, when you want to deal with — look at refractive error and find if they are potentially amblyogenic or not. But again, you have to look at the holistic picture. Not just one at a time. So I will just — as we go through the presentation — tell you what I mean by that. Now let’s look at an example here. As you see in this picture, a one-year-old child comes to us with complaints of constant inward deviation. Since four months of age. And this is the cycloplegic refraction value, which is about +2 diopters. And the fixation assessment shows that the child you resists occlusion of the right eye. This child does not want you to occlude the right eye. So in this particular case, if I have to ask you, what type of amblyopia is this? So I request Shweta to launch the poll. So in this particular case scenario, what is the potential amblyogenic risk factor that you are able to identify, and how would you classify amblyopia? So most of you have given the right answer. So as you see here, we are talking about a one-year-old child for whom the +2 diopter cycloplegic refraction value that we showed here is potentially considered normal for the age. And so in this case, the amblyogenic risk factor is supposed to be strabismic. And so strabismic amblyopia would be the more appropriate answer in this case. And most of you have got it right. So that’s good. And let’s move on to the next scenario. Let’s see how many of you are able to get this, based on the etiology. So now this is a 4-year-old child who is referred from a school vision screening program for further management. And as you would see here, the visual acuity in the right eye is 6/18, left eye is 6/9, the near visual acuities are normal, there is no strabismus that you’re able to identify, and this is the cycloplegic refraction value. So a +1.5 diopters, with 4 diopter cylinder. Axis 180 in the right eye. And left eye is +1.5 diopters here with 0.5 diopter cylinder, axis 180 in the left eye. So take a look at this. Now, if I want you to classify this amblyopia, what could potentially be the type of amblyopia for this particular case scenario? Okay. Okay. So some of you have answered meridional. Some of you have answered anisometropic. Anisometropic is definitely not a wrong answer, though. So meridional amblyopia is a more appropriate answer, because you are looking at anisometropia due to astigmatism in this particular case. So meridional amblyopia is the more appropriate answer. So you can still classify it as anisometropic, but prefer to use the word “meridional”. And I just got a look at one of the questions in the question and answer section. Though I would like to answer it towards the end, I thought that it’s more relevant at this point. So some of you wanted me to simplify the definition for amblyopia more. So what I wanted to tell you is that amblyopia is — you cannot define amblyopia like when there is a visual deprivation, or when there is a visual impairment, for which you are not able to identify the cause. So that’s what used to be the older definition. Or some people would say that any visual acuity of less than 6/9, you can call it amblyopia if there are no physical causes that can be detected during an eye examination. So that was what used to be earlier definitions. But now we are relooking at the definitions, and we are saying that you cannot define amblyopia just based on one visual acuity cutoff, or based on an interocular difference in acuity by more than two lines. Okay? So you can still use the definition of less than 6/9 or greater than two lines of interocular acuity difference. These two are standard definitions. But beyond that, amblyopia also has many other pathophysiological aspects involved into the definition. That’s what I wanted to tell you. Okay. So with that, let’s move on to the clinical investigations, which are more relevant for optometrists, basically. When a child or an adult with amblyopia comes to you, what should you be assessing, or what should you be looking for? So I have categorized the whole assessment into three areas. The number one is basic testing, which is done as part of a routine ophthalmic investigation. For every person. Not just for amblyopes, but for every person. And then comes specific tests, which I have categorized into binocular and monocular components. Let’s first look at the basic testing, before we jump onto the rest too. So in the basic testing, as usual, history taking is the most important aspect. I’ll just highlight some of the key questions that you might have to focus upon, when you are taking history for a child with amblyopia. And then of course your visual acuity, which is basically — I’ve mentioned it as high contrast, because when we measure our Snellen visual acuity or LogMAR visual acuity, we are only measuring the 100% contrast at the highest spatial frequency cutoff. We are not really looking at any other contrast levels. And the next thing is cycloplegic refraction. Very, very important. So before we really diagnose amblyopia, before we want to decide about the refractive prescription, a cycloplegic refraction is mandatory. And of course, a dilated fundus examination. I would also want to emphasize upon keratometry, or measurement of corneal curvature, that you can do either manual keratometry or now autorefractors do come with an inbuilt keratometry, so you can use that to document corneal curvature. In amblyopes, especially as you saw in case two, that was a meridional amblyope. You want to really correlate your refraction with the corneal curvature values that come up. So it’s important to document keratometry. The second thing is keratometry also helps you to determine the accurate axis. Because in children, many times when you do a refraction, you may not be able to refine your RJSCC, and enable the appropriate axis. But prescription of the cylindrical correction at the right axis is very important in the treatment of amblyopia. Even if you’re going to make a 5 degrees error when you’re prescribing high cylinders, that’s going to impact the visual acuity of the child. So it’s very important to be accurate when it comes to documenting the cylindrical axis and the magnitude. Then some of the monocular tests I have mentioned here are the standard assessment of fixation. I will anyway talk about it in detail. Then the contrast sensitivity measurements and ocular accommodation. And the binocular tests — your sensory and motile assessments. And some additional tests I have mentioned here, which some of you might be familiar with, and some of you may not, so I’ll talk about that in detail as well. And then there is an ancillary testing component that I have put here, which I feel is like — in some cases, when you want to understand amblyopia in detail, when it comes to the whole management of myopia, especially amblyopes, myopic amblyopes, who are progressing, or even hyperopic amblyopes, who are rapidly emmetropizing, even documenting ocular biometry is very important for the clinician to be able to know what really happens in the axial length and other ocular structures. And reading speed and other supplemental testing, supplemental testing, like ERG or OCT, to rule out any other potential underlying causes, that can mimic amblyopia. So if the child is on patching and visual acuity is not improving beyond a certain level, visual acuity is flat, and we have ruled out every other cause, then are we missing out something? So these are supplemental tests that could actually add more value in the process. But moving ahead with the history taking, these are some of the aspects that you want to make a note of. Number one, as we already saw, any child with a family history of amblyopia, either in parents or in siblings, is at a high risk of amblyopia. And the developmental milestones — children with developmental disabilities and delayed development are at high risk of amblyopia. And if they have already been diagnosed with amblyopia, and if they are under treatment for amblyopia, then it’s important to know at what age the diagnosis was made, which eye is amblyopic, what is the history of previous treatment that they have undergone so far, including refractive correction, or penalization through occlusion, or pharmacological penalization, or any active vision therapy treatment modalities that they have followed. And very important is how compliant they were to any of the treatments that were proposed by previous practitioners, and that’s going to give you an idea if you are going to initiate some treatment, how compliant they will be. Or should we modify the treatment protocol. And if they are on a patching regimen, then what type of patch, how many hours, how compliant they are, do they do any additional activities when the patch is on, and does the child have any specific difficulty in navigating around or overall, in terms of their quality of life, do they have any specific difficulty when they are on the patch? So these things need to get into the history, when you are specifically investigating for amblyopia. The next thing is, as I already mentioned, getting a proper refraction. I cannot emphasize more on this. But to be super skilled with your retinoscopy, as well as in your cycloplegic refraction, and getting your subjective acceptance done in older amblyopes, or any child who is cooperative. Sometimes we believe that children are not cooperative, but we need not assume that. Wherever possible, a subjective acceptance can be definitely tried. So when it comes to cycloplegic refraction, I was about to tell you that staying on axis is very important, because most of the time, errors can happen in refraction when you go off axis, because of dilated pupils. And this can also result in errors in the axis off cylinder prescriptions. So it’s super important to be very accurate and skilled with your cycloplegic refraction. So the next thing is moving ahead with your visual acuity testing. So I’m not going to really dive deep into this, because I understand that all of you are quite familiar in checking visual acuity, like using age-appropriate visual acuity tests. So I just mentioned some of the commonly used tests, especially when we are dealing with children of different age groups. If you’re dealing with a child like between 0 to 3 years, then you could use any of the preferential-looking tests, OKN, or the Lea symbols, and the HOTV is agreed upon as a gold standard or standard test in amblyopia assessment. And if the child is greater than 3 years, then you could use your ETDRS, your Snellen, Lea symbols, or HOTV. But I would highly recommend that you use a standard visual acuity chart if possible, like use a Lea symbol that uses logarithmic principles. LogMAR principles or the ETDRS charts. And the illiterate-E and Landolt-C of course needs a sense of direction, directional understanding from the child. So usually children up to 7, 7.5 years, they don’t really get the directional understanding so accurate. So you might want to delay the use of these tests until they turn 7, 7.5. But you can go ahead and use your other picture-based or letter-based matching cards or whatever. Whichever is appropriate. But visual acuity is the starting point in amblyopia diagnosis. So getting an accurate estimate of visual acuity is very important. Number one. Number two is, of course, when the child comes for regular follow-ups, it’s always important to check the amblyopic eye’s visual acuity first, and to change the charts also, because kids are very, very shrewd. They tend to memorize your visual acuity charts. So it’s very important to change the charts or use computer-based charts. That randomizes the letter presentations. And that’s your standard ETDRS letter charts. So if you see these — as I told, the Lea symbols are the standard. ETDRS. The spacing of the letters and between the letters and between the lines, they all follow a logarithmic progression. So they are more appropriate when it comes to testing for visual acuity. Then these guys are preferential looking cards. The most important aspect that many of us deal with in amblyopia testing is basically crowding phenomenon. So it’s established that the lateral inhibitions that happen in the retina when a stimulus falls on the retina — the visual processes that happen — amblyopes have some issues with the lateral inhibition. So when you have two targets or three targets simultaneously, that are just simply present, the system, the visual system, will confuse. So they might actually give poorer responses when the visual acuity — when the letters are presented together, or in a crowded fashion. So this is an inherent deficit in the amblyopic visual system. But having said that, when you’re going to use single-symbol presentations, you have to be very cautious that that’s going to overestimate the visual acuity. Because now that you’re removing crowding from the equation, it’s going to of course overestimate the visual acuity. So you have to keep two things in mind. Number one, you have to use a standard visual acuity chart for measuring visual acuity. Number two, when you want to measure crowding phenomenon, whether crowding is present or not, then we would recommend using — as you see here, the same Lea symbols with a crowding bar. You can show it isolated, like the single symbol Lea that is shown here, but you can use crowding bars, so that you are not really overestimating visual acuity. And then number two is you can use computer-based visual acuity testing, rather than pointing. So it’s always recommended not to point out the letters, because that’s going to overestimate. So if a kid has difficulty reading letters continuously, you can use arrows like this, and move arrows adjacently, for them to focus on one letter at a time. So the way it is understood that single letter visual acuity estimation is better, it’s also imperative to understand that it overestimates the visual acuity. So you should be using crowding bars. And that’s how you take care of the crowding phenomenon in amblyopia. The next few sets of tests are all to do with fixation preference. So the first is your standard fixation preference test. When I say SFPT, which stands for standard fixation preference test — so this is basically your central, steady, and maintain. So what you want to do is you want to close one of the eyes, and then look for the ability of the amblyopic eye to fixate. It’s also important to show fine detail targets or an accommodative target. Or targets closer to the visual acuity of the child. So that the child really fixates at the target. Or you can use colorful lights and toys, which attract the attention. So basically the child needs to fixate. Now, when you close the dominant eye, or the good eye, and ask the child to fixate with the amblyopic eye, what do you need to look for? You need to look for if the child is able to fixate and hold the fixation for greater than five seconds. That indicates that the eye has normal fixation or potentially has normal visual acuity. But if the child holds only briefly or momentarily or less than three seconds, before it refixates to the dominant eye, then that indicates that there is a fixation preference. So this is the criteria that Dr. Wright proposed, when you want to classify or you want to look at: Does the child have any fixation preference? So this is the test that you will use when you are dealing with the strabismic amblyope. So if you are dealing with a child who has either an esotropia or an exotropia, then you can use your CSM testing. But if you are dealing with a child who is anisometropic, who is apparently orthophoric, or you are dealing with a child who has microtropia, which is otherwise like a small angle strabismus, less than, say, 8 prisms, then Wright proposes that we use what we call the induced tropia test. And that is basically using a 10 prism or a 12 prisms, as you see here. Two, check the preference. Fixation preference. So how do you do that? So if you see here, in this particular video, I’m just holding a 12 prism base down, in front of one eye, and then looking out — looking for the eye movements. So maybe because I don’t know — because of your internet connectivity, some of you might be seeing it catching up really slow. But as you can see, if the eye is really — see, this is the dominant eye. So you can really see that it makes a vertical movement and then comes back. But when the same vertical prism is held before the amblyopic eye, because the shift in the image that happens in the retina is happening within the foveal zone, and so the person is not really appreciating the diplopia. So in this case, the eye is not going to make any movements. So in this particular case, it’s basically unmaintained fixation in the right eye, which is the amblyopic eye, whereas the left eye is the dominant eye, and that is showing normal fixation. Or you could go ahead and use the common 4 prism base-out test, which is what we use when we do — when we test for microtropia. So whenever you hold up 4 prisms, or a prism base-out, you know that the eye moves towards the apex. So what you have to look for is: You put the prisms and immediately look for the movement of the eye. So now, in this case, when the 4 prism base-out is held in front of the amblyopic eye, you are not really seeing any movement of the eye. So I’ll just play it once again. So generally you can look at the dominant eye. So look at the other eye. It’s easy to really look at the movement that the other eye makes. So both eyes are kind of — like, the eye with the prism moves towards the nose, and the other eye is making a yoked movement away from the nose. But when you are keeping the prisms in front of the amblyopic eye, you’re not really able to make out any eye movements. So this is again indicative of a central suppression scotoma or a microtropia. So that’s what the 4-prism base-out test is going to help you with. So if there is no movement that is detected, like you keep a prism, the eye is not really appreciating the diplopic movement, then the eye is not going to make any movements, and that means it’s positive. So when you say positive, it indicates that the eye is amblyopic, and when we say negative, it indicates that the eye has apparently normal fixation or does not have a central suppression scotoma. Then the last test in this category is the Bruckner’s test or the reflection test. So as you see here, we use the direct ophthalmoscopic light. You can show the light as broad as possible so that it equally illuminates both the eyes. And the test is preferably done at a distance of 1 meter, so you dial in high magnification and look through the direct ophthalmoscope, and look at the reflex that comes — the reflection that comes from both the eyes. And the eye that is either strabismic or anisometropic is going to show a more brighter and pale reflex, so in this case, the left eye is potentially amblyopic. But the eye that is good or non-amblyopic is going to show a more darker and more deep red reflex. Okay? So whichever eye that is going to show a pale and white reflex is indicative of amblyopia, when you do a Bruckner’s red reflex test. So this test — you need to be careful when you are doing this test in microtropes, because in microtropia, you may not be able to find out. It will look as if both the reflexes are of the same brightness. So for microtropia, it’s always preferable to do other tests, such as your 4-prism base-out test. But this is usually applicable when there is either an anisometropic component or a strabismic component. And even in the case of anisometropic amblyopia, when there is high refractive errors, you just can keep going a little back from 1 meter. Like, you can go up to 2 to 3 meters, and you can look at the — you can figure out the crescents that come out through these red reflexes, and many of the current technologies like the handheld autorefraction, like the photorefractors, utilize this red reflex as an additional component to estimating the refractive error. So you not only get refractive error estimation, but you also get to see the red reflex as part of these tests. So the next is our motor evaluation. So getting your ocular motility test done. And an accurate estimation of the ocular alignment, if they have strabismus. Then with the best refractive correction in place, you might want to do your cover test and neutralize the strabismic deviation. Okay? So that is the next aspect. Then moving a little bit deep into the sensory testing that you would do in amblyopia, the two important tests, which are going to give you a lot of information about the depth of amblyopia, and which is also going to serve as key clinical indicators when the child is on amblyopia treatment, are stereopsis and Worth-Four-Dot. So stereopsis, as you would see here, you would use a standard Randot stereo test, and it’s very, very important to be checking for both the global stereopsis, which is the random dots, that are devoid of monocular cues, so use global stereopsis. When you want to really pick up the actual presence of stereopsis. Because when you use local stereopsis, like the Worth-Circular Animals, there are monocular cues that are present. So even if the child lacks binocularity, they might still be able to pass about one to two levels of stereopsis with both your circles and animals. So it’s highly recommended that we get the global stereopsis done. And even in microtropia, you might see that children may lack global stereopsis, but then they would pass local stereopsis. So it’s important that you do both the estimations. The second thing is getting your Worth-Four-Dot test. Many of us underestimate the utility of Worth-Four-Dot in getting the suppression, the depth of suppression, in amblyopia. So of course all of us know that we have to do Worth-Four-Dot at both distance, at 6 meters, and at near, like 33 centimeters to 40 centimeters. But I would also recommend that you do it under normal room light illumination, as well as with your dim illumination. Now, why would you do it under two light levels? It’s because you want to look at how the depth of amblyopia is behaving. So, for example, a child that reports fusion under normal room light and becomes diplopic under dim room light, that tells you that the fusion is not strong enough. So in the absence of peripheral fusion cues, the fusion breaks and the person becomes diplopic. The second thing is: You can see this also. Like, some kids might report suppression under photopic conditions, and then when you dim the room lights off, they would be able to appreciate the Worth-Four-Dots better, and they will report fusion. So all these are clear indications of how well the fusion system is responding to different light levels. Because as you know, amblyopia is not just a problem in visual acuity. It’s also a problem with contrast. So sometimes enhancements of contrast can facilitate the fusional response of the child. So that can also add to the response that you might get with Worth-Four-Dot. But more than that, as you see here, when you’re doing your Worth-Four-Dot, you can get different responses. But what I want to add at this point is what I call as the Worth-Four-Dot walk-away test. So in Worth-Four-Dot walk-away test, what you basically do is, after you do your cover test, you look for any microtropia, basically. So this is a more accurate estimation for microtropia, basically. So you do the unilateral cover test. And as you would know, if there is a microtropia, you’re not going to be seeing any movements in your cover test. So would you go ahead and recheck with your alternate cover test. Then you do your near Worth-Four-Dot. Okay? So in near Worth-Four-Dot, if the child reports suppression, then of course, even at 40 centimeters, somebody is reporting suppression, so you don’t proceed further. You stop there. But they report fusion. Then what do you do? You just keep going back and back with the handheld Worth-Four-Dot. And you look at if the fusion becomes suppression at any point. So at 40 centimeters, they report four dots. You go to 50. You go to 1. You go to 2. And then look at if at any distance the fusion response turns into suppression. Now, here, remember that almost 70% of normal observers also report suppression when you go beyond 2 meters. So when you go beyond 2 meters, because these are really tiny dots, the near Worth-Four-Dot, so you will start to report suppression beyond two meters, which is normal. But if the person reports suppression at less than 2 meters, like as you see here, even before 2 meters, if they’re going to report suppression, then you go ahead and do your Bagolini test, which I will show you next. And then look for the absence of the central portion of the streak. And then you go ahead and document the stereopsis, and if you see that they only have peripheral stereopsis, then that is indicative of monofixation. Now, you could ask: What is the relevance of finding out whether they have this peripheral fusion present? Then it comes to clinical management. So what happens when you are putting the child on to patch and treatment, even in the absence of significant clinical — clinically significant improvements in visual acuity? You might start to see that they report now fusion at more than 2 meters. I mean, they report loss of fusion at only more than 2 meters. So they might start to really show peripheral fusion at a much larger range. So earlier, even before 2 meters, they reported loss of fusion. Now they can maintain fusion even up to 2 meters. So that is again telling you: Yes. There is a development of fusion, peripheral fusion, that is happening. So it goes beyond just estimation of visual acuity. And this is a reference which is, I think, apparently a masters or a PhD work done at the Pacific University, which is really accessible. You can go and read the entire thesis, where they have done this particular experiment. So as I told you, now that you do your Worth-Four-Dot at 40, and say the person reports suppression at 1 meter, then you go ahead and do your Bagolini. So as you see here, these are Bagolini lenses. And then your specific torch, pen torch, that you will use for Bagolini, and how the lenses — the light is converted into streaks through these Bagolini lenses is what you see here in this picture. So the patient is holding the Bagolini, and this is how they will see it. So when you hold a streak of light, they’re apparently supposed to be seeing two streaks of light that looks like an X. And that cross at the center of the light source. Okay? So these are different potential responses. So as you see here, the middle one — there you’re seeing the light source in the center, with the perfect Xs, indicative of fusion. Then the bottom one, towards your left, where you see a missing of the streak in 1,9, is indicative of a microtropia. So if you see this, in addition to your Worth-Four-Dot walk-away, then you can easily diagnose that this child has microtropia. Or if you see a complete absence of one of the streaks, that’s indicative of total suppression, and the top two responses are indicative of diplopia. Uncrossed and crossed diplopia. So these are different responses that you can get out of Bagolini. And Bagolini, again, is a very useful test, because it’s the least dissociating test through which you can get the sensory fusion responses under normal illumination conditions. Okay? So it’s more or less close to natural viewing situation, where you can get the fusional response. The next thing is: Okay, now that I have done my Bagolini, I want to know: What is the extent of suppression? Okay? So how deep is the suppression of the amblyopic eye? So as you see here, we can use neutral density filters. In the right corner of the PowerPoint, you can see that the patient is holding the Bagolini, and then a neutral density filter is held in front of the good eye. So basically what we’re trying to do: We’re trying to reduce the contrast of the good eye, until the patient starts to appreciate the streak in the amblyopic case. You’re trying to reduce the competition that the good eye is giving to the amblyopic eye, and thereby you are enhancing the response of the amblyopic eye. So that’s how you find the depth of suppression. So the neutral density filter will be numbered anywhere from 03 to 18. And that means anywhere from 0.3 to 1.8 log units. Because that’s what it indicates. And also, as the log units increase, it’s also reducing the transmittance of the light. So it’s slowly cutting down the amount of light that is reaching the good eye. But whereas the amblyopic eye continues to see the same intensity of the light — so let’s just now see this. So suppose you’re showing the Bagolini, and the patient sees that I’m only seeing the line by the good eye — so the amblyopic eye’s line is not visible. Okay? Then what you see: Slowly increase your neutral density filter in front of the good eye. And as you see here, now the contrast of the good eye is coming down. But the amblyopic eye also now starts to take part in this binocular competition. So the amblyopic eye starts to see. So when the good eye sees really dull, now the amblyopic eye starts to overtake. Now 1.2 log units is the suppression, the magnitude of suppression of the amblyopic eye. So that’s how you quantify the depth of suppression. So that’s how you quantify the depth of suppression. And then you can keep quantifying as the patching treatment is given, or any amblyopia treatment is given. You can look at how the suppression magnitude is reducing. So this is one way that you can use your Bagolini, along with neutral density filters, to quantify suppression. The next most important test is looking for eccentric fixation. Many times, we overlook this. Especially in anisometropic amblyopia. Especially in high myopic or high hyperopic amblyopes, there’s almost always a small microtropic component that is present. Okay? And this eccentric fixation is generally present even under monocular viewing conditions. And so you have to use your direct ophthalmoscope, and that’s what we call visuoscopy, to quantify the amount of eccentric fixation. So I recently came across a paper. You can even use the streak of your ophthalmoscope. The standard test is using your calibrated line target that you see here, the circle and the line targets. But some people say that if you’re dealing with a preverbal child or a child less than 3 years of age, who cannot respond to this particular test, then you can even use the ophthalmoscope streak, and just look into the eye, basically. Like, you just show a vertical streak, look into the eye, and then see where the fovea is located, with the response to this particular streak. And this is a crude way of estimating if there is a gross eccentric fixation present or not. But the standard way of testing is to do your visuoscopy. There are four things you look when you do your direct ophthalmoscopy. Number one, you are looking at the localization, whether it is located on the fovea or it’s off the fovea. Second, if it is off the fovea, how much off? The third is: Is it nasal to the fovea or temporal to the fovea? The last is: How steady is the fixation? Is it like — when you say that, look at the center of the circle. So you always say I’m going to show this particular target. I’m gonna show the circle inside your eyes. And I want you to look at the center of the middle circle. So you can even use funny words. Like you have to aim and shoot at the center, or keep looking at the center, or whatever. And then you look for the steadiness. Whether the child is able to hold fixation in the center of this particular circle. And the clinical relevance is that whenever you see an eccentricity, it’s assumed that for every half degree of eccentricity, visual acuity reduces by one Snellen line. So this is how you get to do this procedure. So this is basically the target. You either project it on a table or the child’s hand, and first familiarize the child with what they’re supposed to do. So you have to tell that there are many circles that you see. But this is the target that you will see in a Keeler ophthalmoscope. So you have to basically look at the middle of the center circle. So the center circle is about 2 prism diopters, and then everything is about 1 prism diopter from there on, so 2, 3, 4, 5, and you can go further than that. So usually you don’t see more than 3 or 4 prisms of eccentric fixation, and that is the reason why the circle size is restricted to this. So you show this target. First to the good eye always. Because you want the subject to familiarize themselves, to know what exactly they need to do. So you show to the good eye, and you will really get the fovea right on the center. And occlusion of the other eye is very important. Sometimes we forgot to occlude the other eye. So you always occlude the other eye. Now, here I’m just trying to look into the amblyopic eye. So the child is fixating at the center of the streak. So I’m trying to look at the steadiness, as I told you. The localization, the steadiness, the magnitude, and the direction of the eccentric fixation. So assume that this is what we see. Okay? So this is, as you know, the image of the left eye. And you project your direct ophthalmoscope image, and then this is what you see. The diamond that you see here indicates the fovea. And so you know now that the circle is nasal to the fovea. So the diamond is where the fovea is falling. So the circle is nasal to the fovea. That’s number one. Number two: How much prism diopters. As I told you, the circle is one prism diopter on either end. The whole circle is 2 prisms. So you have to count one towards one side. So 1, 2. So it’s about 2 prism diopters of nasal eccentric fixation. Now, for a clinician, we want to know: Okay, now the child has about 2 prism diopters of eccentric fixation. Can I equate this to visual acuity? Yes, you can equate this to visual acuity. You always add 1 to the amount of eccentric fixation that you see. And so you get about 3, and that stands for a minimum angle of resolution. So you add 1 to the eccentric fixation, and that becomes a minimum angle. To simplify this, just multiply this by 20, and that becomes 60. So 20/60 is the estimated visual acuity for this particular child. So when you want to write it down, you use a positive sign for nasal eccentric fixation, and a negative sign — it’s only for documentation. But in the formula, you always just put directly the value, and then get the minimum angle of resolution. Convert it into log MAR acuity. Now, in this case, you are finding 2 prism diopters of eccentric fixation. But the visual acuity estimation is, say, 20/40. Okay? Then either the visual acuity estimation is wrong, or the eccentric fixation estimation is wrong. Because generally there is a very good correlation between the amount of eccentric fixation and the drop in visual acuity. So now that you have understood this, I’m going to conduct a poll, where I want you to find the estimated level of visual acuity. So I’m going to give you an eccentric fixation amount. So remember, add 1 to that value. And then you’ll get the MAR, and you’ll have to convert that to LogMAR. That’s all. So if you multiply that by 20, you get the 60 in this case. So 20/60 becomes the expected visual acuity. Okay? So I’m going to run the poll now. So if a child has 3 prism diopters of eccentric fixation, what is the expected visual acuity for the particular child? So most of you got it right. Perfect. It’s 20/80. Because 3+1 becomes 4. Minimum angle of resolution. So 4 multiplied by 20 becomes 80, so 20/80. This is how you actually look at the eccentric fixation. And then try to equate it to visual acuity. And this is the table that you can use it as a reference. Like if you see some amount of eccentricity, what is the equivalent visual acuity? So you will have access to this PowerPoint in the Cybersight website. You can always take a look at it. No worries. Okay. The next thing is: You can use the macula integrity tester, which is nothing but a modification of the conventional Haidinger brushes. Which is basically like the entoptic phenomenon-based testing, where, when you look through the blue filters, you you actually get to see the propeller that you see here. So here the propeller is horizontally oriented. Here it is obliquely oriented. So here it is vertically oriented. So the center, the fixation — there’s a fixation point, and there’s the center of this propeller. So the center of the propeller serves as a tag for the fovea. Because it’s supposed to stimulate the fovea. Okay? So wherever is the center of this propeller, compared to the fixation point, you can find out the amount of eccentric fixation. We used this quite a lot, not just in estimation of eccentric fixation, but also in the treatment process. Okay? Like, to kind of break the anomalous correspondence pattern and the eccentric fixation pattern. This is a very valuable tool. The next thing is getting your accommodation assessed. Because many recent studies — this is one specific study that I want you to remember — that children with amblyopia, especially unilateral amblyopia, the accommodative response is poorer in the amblyopic eye. So this has greater implications for us, because it’s important to understand whether these children — that they’re able to read comfortably, or they can have blurred vision, even when the child is patched. You know, we give near acuities, when the child is given patching treatment. But when they have poor accommodation response, whatever they’re trying to do could be blurred. So we have to look at how to improve the accommodation response of this particular child. So if you have to assess it, then your standard monocular estimation method, retinoscopy, as you see here, our optometrist is trying to do the monocular estimation method, where she’s just using lenses to look at the — to neutralize the accommodative error. Or you could use — I’m sorry. This is completely turned. But this is what is called an open field autorefractor, where you can actually get the objective accommodation response from using an autorefractor. Okay? But this is a very simple clinical tool that you can always use. But what is more important is to ask the child to be reading out the letters that is written here, and make sure that the child is accurately fixating. So this is one specific test that I would recommend in every unilateral amblyope, to find out if there are accommodation errors. Then your low contrast visual acuity. Earlier, people used to measure contrast sensitivity, but you can even use low contrast visual acuity, because during the patching treatment or any amblyopia treatment, we can look at improvements in the visual acuity. Again, just to cite the evidence, because of the issues with higher order aberrations in the amblyopic visual system, they apparently have inbuilt or inherent loss of contrast. So this is a study that looked at — if I correct these higher order aberrations and train contrast sensitivity, how does the system behave? So this study shows the effect of perceptual learning on improving contrast sensitivity. But even otherwise, many studies you have shown that you can use your vision therapy or perceptual learning to not just improve visual acuity, but also contrast sensitivity. Now, these are some of the additional measurements. But I will not go into the detail of these tests. But why is this important? I’ll just tell one point at this stage. Because more and more studies are coming out in this particular area, that children, even when they are treated for amblyopia, they have poor reading abilities. And if you are seeing a child that says that they have struggles reading, or they have some difficulty reading, it is important to look out for these abilities. And you might want to look at additional strategies that can help them. Like using either more spaced letters, or using specific lined books, or when they want to — like, large font books. You might just think that they have good near vision, so they might be able to read well, but because of the crowding, it is important to remember that the reading ability can be impaired. Now, I will finish my presentation with an overview of: How do we manage amblyopia? Overall, now that we have done testing, we have assessed monocular and binocular functions, the overall goal of amblyopia is of course to improve monocular and binocular visual functions. And the prognosis, as we all know, is dependent on very many factors, including age, vision, cause and severity of amblyope, duration, and complaints. So before I just summarize that, I want to take a poll at this point to know your understanding of the current evidence that’s used in amblyopia treatment. All of us are aware of the PEDIG studies that have, I think — currently it’s on study number 20 or 21. So they’ve come out with a number of results that has standardized the way that people treat amblyopia. So in this particular case, if you are seeing a 5-year-old child with anisometropic amblyopia, with plano refractive error in one eye and -6 in the other, what would you do? Will you prescribe full correction and start part-time patching? Or you will prescribe full correction and start full-time patching? Or you would only give spectacles and review at 6 to 8 weeks? Or you would give say -3 or -4 and start part-time? Which one would you choose? And you can just choose whichever that you are currently following, or you feel is more appropriate for this particular case. Okay. So there does seem to be wide variation in the response, as I expected. And many of you would want to prescribe full correction and start part-time occlusion. Okay. And some of you would want to prescribe full correction and review at 6 to 8 weeks. Okay. So what is recommended from evidence? Basically it’s to only prescribe glasses and review at 6 to 8 weeks, and not do anything. Okay? The reason is because I’m not getting into the detail of this particular — the entire PEDIG protocols, but this is an outline. So generally, you don’t do anything. You only prescribe full refractive correction, even if the amblyopia is moderate. Follow up every 6 to 8 weeks. And if the visual acuity improves by more than 2 lines, you just keep continuing the refractive adaptation. But if the visual acuity plateaus, or if the improvement is not happening as expected, then we initiate part-time occlusion. Okay? And the initiation is usually only part-time. 2 to 6 hours. And then when maximum visual acuity is achieved, then you can taper the treatment. Now, what I recommend people who are listening to this lecture — is to go and listen to another lecture. There this entire treatment is so nicely summarized by Dr. Jenelle. So she has done this presentation, I think, very recently. The entire PEDIG protocol, with case examples, she’s dealt with. So if you go and listen to this particular presentation in this link, you will get to know why I told that way. Like go ahead with only refractive adaptation. But now that you’ve started refractive adaptation, and if you want to start any therapy for amblyopia, then this is the whole sequence. If any of you want to listen more in detail, you can send your feedback, and we can do a full lecture only on this alone. But if you look at the graph steps, whenever we treat any amblyopic patient, our goal is to start with full refractive correction, improve monocular functions, go improve peripheral fusion, then go improve foveal fusion, then establish binocular vision in free space, and start a home maintenance program. So this is the general vision therapy protocol that we follow. And some of the protocols that we use go like this. We start what is called as the MIB, monocular in binocular field. Go to bi-ocular treatments. Binocular. And intersensory integration. So just to give you a feel of: Why do we actually talk about vision therapy, or even any advanced treatments in amblyopia management? Even when there are not really well established evidence for some of these innovations? Mainly when we deal with these children, we know that compliance issues are always there, when we put these children on patching. And there are well established evidence that children have — who are on patching — develop allergic reactions. There is social stigma and quality of life issues, and peer pressure, and other things associated with patching. And if the child is put on atropine penalization, and then they have allergic reaction and photosensitivity issues, and when you are able to provide some of these innovative treatments, you’re able to reduce the treatment duration, you’re able to engage the child much more, especially when it comes to younger. When it comes to older, you have very limited window for visual acuity to be improved. So it’s always better to be more aggressive with your treatment. And you are able to achieve — just beyond improving visual acuity, you are able to achieve improvements in stereopsis, improvements in fusion, and these treatment modalities have kind of revolutionized the follow-up of treatment. The clinician can sit at one end. The patient can undergo the treatment at the other end. And you will be able to remotely follow up the improvements in the vision. So that’s the reason why some of these inventions are like — these are some of the studies that have been published very recently, about the importance of dichoptic-based video treatments, or even — this study is a very well conducted study, where they have looked at contrast-rebalanced movies. Like, remember the Bagolini test that we did, where we purposefully dimmed the contrast of the good eye? So the same principle is used in this vision therapy also. Where you purposefully reduce the contrast of the good eye, such that the eye is able to work together. Binocular summation is happening. And you’re able to improve binocularity, along with visual acuity. Now, the important thing is: In this particular study, in two weeks of treatment, they have been able to achieve the same result that — with occlusion therapy — that the child was able to achieve in 3 to 4 months. The two groups — one was put on occlusion. The other was put on binocular games. So within 2 weeks, you’re able to achieve something which otherwise is gonna take you 4 months. So I think it’s important that we really look at some of these treatment modalities. As I told you, I don’t have any financial disclosures. But these are some of the advances that you can go ahead and look. One of that is REM MED virtual reality. This is BYNOCS, which is a game based on dyke optic-based video games. The third is what is called RevitalVision, where it’s based on Gabor patch-based images, to stimulate the lateral interactions, as well as binocularity. So when do we use all these? In this particular case, where this child was poorly compliant to patching for almost 2 years, the patching was done. Visual acuity did not improve beyond 6/12. When the child was shifted to dyke optic treatment, in 10 sessions, 1 hour per day, visual acuity improved to 6/7.5, and stereopsis also improved. So these are real examples of some of our children who improved with these treatments. This, again, a 12-year-old, who had both microtropia and anisotropic amblyopia, basically combined mechanism. Again, visual acuity was plateaued. We started with virtual reality-based therapy. Again, in 10 sessions, visual acuity improved. So these therapies kind of, you know, help you to get rid of the plateaus that you would be struggling otherwise. In amblyopia treatments. So this is like a kit that I just wanted to show you, all this testing that we discussed so far. Which has your stereopsis, your near Worth-Four-Dot foveal, especially the smaller targets, your Bagolini, importance of accommodation testing, your anomalous correspondence. I didn’t get into anomalous correspondence, due to the time. And your standard visual acuity charts. Some of the references. And I take this opportunity to invite all of you to our upcoming international vision science and optometry conference in August. Between 13 to 16th. Happening in Chennai. So you can go into our website. EIVOC2020.org to learn more. There are many more topics and many more hands-on workshops that you get to attend. So even ophthalmologists who are attending this session can see if you can send your optometrists to get trained in a variety of areas. And any other further feedback or topics that you want to cover, you can email me, as well as Cybersight, Mrs. Shweta. Thank you, everybody, for your patient listening.

January 28, 2020

Last Updated: October 31, 2022

5 thoughts on “Lecture: Assessment of Amblyopia – What to Look Out For?”

  1. I would like to thank Dr. Jameel Rizwana and Cybersight team. The presentation is very interesting and impressive. It’s very helpful and easy to understand. We can prevent the loss of vision from detecting early amblyopia completely. Would you like to send me your good presentation? I’am very happy to see it. I’m looking forward to seeing you.
    Have a nice day!


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