 All right, I'm here to talk to you today about some of the techniques that we use to examine vision in children. And you can imagine that there's a wide range of techniques given that some children are pre-verbal and can't read our eye chart while others have limited ability to read letters and numbers. And so we do tailor our vision testing to the age of the child and to the pathology that we're looking for. And so we're going to talk and highlight some of the most important things that we examine today in our lecture. So we'll start, though, with what's normal at birth. We like to see that the child reacts to light. And in fact, if the child's born preterm, we can see this response after about 30 weeks of gestational age. So this we consider to be a normal response at birth. We then like to see that the child can maintain eye contact with other humans, particularly lock onto faces, around six weeks of age to two months. We don't reliably measure visual fixation or following behavior until the child's about three months of age. And then we can start to measure a formal visual acuity in terms of reading numbers and letters on an eye chart around about two years of age, depending on the child. And finally, at five years of age, we like to reliably see that the child can read the SNELIN eye chart that we're most familiar with and that we test adult vision with. So let's now focus on the first two perimeters, our fairly self-explanatory blink to light and fixation on faces. But let's talk about how we assess for fixation and following behavior starting around three months of age. There are multiple ways we can do this. The first category would be an indirect assessment. We can talk to the parents and say historically, does your child look at things and follow them in space? We can also test directly whether the patient can fix and follow a target. We also have a method called the CSM method. We'll talk a little bit more about in a moment to kind of more quantify this behavior. And then finally, we have based on prism testing to really understand the fixation behavior of each eye individually. We also can test visual acuity more directly in this population using the phenomenon of optokinetic misdiagnosis with an OK-indra. We can use preferential looking tests that we'll talk a little bit more, teller visual acuity is an example of this. And then finally, we can use visually evoked potentials, which is an electrophysiology technique that measures the speed of transmission of a visual stimulus to the brain. So we'll start with our assessment of a fix and follow behavior. This is really the most commonly tested form of vision in this age range. So you can see this preverbal child pictured here. And these pictures are from the text pediatric ophthalmology. You can see on the slide, and it's written by my mentor Ed Wilson at Storm Eye Institute. And you can see him pictured here. He's testing the ability of this child to look at the toy he's presenting the child with. And the fixation target in children is really important. They're not going to look at something boring. They just won't, especially at this age. So you have to have toys and you have to engage them and interact with them. So you can see this child just naturally wants to look at a toy. We use that to move the toy around, see how the child's eyes move, to see if they move conjugately in all directions of gaze, and to see if the child can continue to maintain fixation on that toy throughout the testing. And so that's pictured in here, but then we don't want to forget that we also need to test each eye individually. And so you can see this in the second picture. We're covering up one eye and trying to understand whether the child maintains fixation on the target that we're testing. So that's a very important perimeter in our fix and follow modality. And we'll move on now to the central study maintained, which is historically a very classic way of representing preverbal child's vision. So C stands for central and it refers to the corneal light reflex. And it also importantly is only referring to fixation under monocular conditions. So when one eye is covered, the eye that's looking at your target is the corneal light reflex well centered. The S stands for steadiness of fixation. Again, this is under monocular conditions. And so if you're holding the fixation target stationary or slowly moving the target, does the child's eye fixation remain steady and slowly follow the target as well? You could imagine this would not be true. For example, in a child with nystagmus, they would be unsteady. But a child that can look and follow with each eye individually in a steady fashion would have a normal perimeter for this S. And then M is unique because it's tested under binocular conditions unlike C and S. And this is the ability to maintain fixation with both eyes well aligned when both eyes are fixing on the target. And why do we do this? Because we're not really quantifying vision in a way that we classically think about for adults on an eye chart. We don't have numbers that tell us, oh, their vision is 2050. Well we do this because it's a very important perimeter for normal visual development. And so the thing that we're most interested in for these kids is that the eyes are equally performing on our visual testing that there's not a preference of one eye over the other eye. And the reason being that as you can see here, if a growing child's eye does not provide a clear focused image to the developing brain, that can result in permanent irreversible vision loss that extends into adulthood and can't be treated after that age. And so when we're testing the use of each eye individually, we are asking ourselves, does this child use each eye equally and therefore do they have normal visual development? So it's a very important perimeter, but it's a little bit different way to think about it than we do in adults. So thinking about this more, another way we can sort this out, because every child's different. So sometimes in one child, you can more easily test in one way and then in another child, you might use a slightly different technique to get the information you need. So this is a little bit different technique that you can use to decide if there's a preferred eye. And so this child, you can see when you cover one eye, the child is unhappy. When you cover the other eye, the child doesn't really care. And so that tells you that the child may have a preference for, in this case, it would be the left eye, the eye that the child is unhappy when you cover. Another way to sort this out is to essentially give the child double vision, as you can see pictured in the lower image. And again, this is from Dr. Wilson's book. But this only works in a child who has straight eyes. So if a child has under binocular conditions where both eyes open, if the eyes are not straight, then the eye looking straight ahead and fixing on the target is the dominant eye. That can alternate, or it can be the same all the time, and that's an important thing to assess. But it's trickier when the eyes are straight. You still have to answer whether there's a dominant eye. But to sort this out, you can give the child two images, one from each eye, and you do this with a base down prism. Usually we use about a 20 prism diopter unit so that the images are sufficiently separated in space that the child can see the two separate images, but they're not too far away that the child wouldn't notice that there are two images. So that's why we use the 20 prism diopter unit. And you can see we put it base down over each eye. And what we want to see here is that the child will use each eye to look at the image that you're presenting. So you also have a fixation target as pictured here for the child to look at. And the fixation target is going to be double. And then you ask, well, in this situation, it looks like the child is looking up and the base down prism is over this right eye. The upper image is being produced over the right eye. And so in this case, the child's using the right eye. But if you go to this image, the second image, the base down prism is now over the left eye. So if the child were using the left eye, similarly, he would be looking at the upper image. But you can see he's not. He's looking straight ahead at the lower image. And that means that the child still is using the right eye. So the child prefers the right eye. And therefore, we have to investigate why the child's not using the left eye. That's how you use this test. So when we talk about approximation of actual visual acuity, which is appropriate in some circumstances, for example, a child that comes in and isn't tracking and the parents are worried the child can't see, one thing you can do is use an OKN drum as pictured here. And if the child tracks the OKN drum, we say that they have a range of about 2200 to 2400 vision reliably if they're tracking the OKN drum as you rotate it. And you can see here that as the child gets older, we can actually estimate that they are having improved vision as they can track the OKN drum. So this can be very helpful. We also can use the preferential looking test as we mentioned earlier. And this is based on the principle that infants demonstrate a greater tendency to fix on a pattern stimulus rather than a homogeneous field. And so we have some cards called teller cards that have a grading appearance on them. And some of the grading is more coarse, while others is more, other cards have more fine grading and the more fine grading appears more like a homogeneous field. So essentially you want to see which pattern the child will preferentially look at. And this is done as you can see pictured with both eyes open. The examiner is behind the pictures being presented to the child because you don't want anything distracting the child's gaze. And so the examiner is actually looking through a little peephole that's designed in the test itself to determine which pattern stimulus the child will look at. And as the child will look at a more fine pattern stimulus, you can approximate that they're having improved vision with that. And so you can see here that normal vision is approximately 20, 30 by age two when testing with this modality. All right, so we're moving on to children who are around age two, two to four or five years old who are now becoming more verbal. They don't have a good command potentially of letters and numbers. So we can't just ask them to read this Nell and I chart, but we can ask them to read certain I charts. And so some of these are, for example, Allen picture charts. This does often overestimate a child's visual acuity and per our BCSC series, the normal age range within an age range of two to five years, the normal visual acuity with this particular type of testing can range from 2020 to 2040. There are other testing methods that I prefer in this age range called the HOTV or LEA testing. There are two separate modalities pictured here, HOTV obviously here, LEA testing here, but the unique thing about these images is that they're palindrome. So they're the exact same image on the right and left and in this age range of two to five years, children do, it is a normal developmental milestone that they could become confused at working out right and left aspects of an image. And so this just takes that out of the equation completely. And therefore, I think it's a little bit more reliable way to test vision in this age range. And the thing, another thing I like about it, you can obviously use cards for near vision and you can test each eye individually, which is really important. You can start doing that at this age, but then it with distance vision, you can also use this as a matching technique so you can give them the near card, but also present them with one of the images at a distance and ask them to match what it is, even if they're shy or they don't feel comfortable verbalizing what they see. So there are different ways this can be done, but I think overall these are very effective ways to start to assign a traditional measure of visual acuity to children within the age range. And using these testing methods, similarly to the Allen cards, we would expect if a child had normal vision, they would measure about 20-20 to 20-40 with distance vision testing. Alright, and then finally, if you have concern that the child has a preferred eye that might be termed amblyopia and we'll discuss that definition in a little bit more detail, with these modalities as opposed to the Allen testing, you can use a crowding bar phenomenon which more accurately will represent the true visual acuity of a potentially weaker eye. So that's another reason why that testing is helpful. So finally, you're all familiar with Snellen eye chart testing, we can start to use this depending on the child at about five years of age. If the child can read the Snellen acuity prior to that, then by all means test it. Usually that's not reliably seen until about five. And we should present the child with letters in a line for most accurate vision testing. Single letters can overestimate the child's vision. We also certainly want to be testing one eye at a time at this age. And you have to make sure that if you have concerns that one eye has better vision than the other, a child will cheat, not because they're trying to deceive you, they're just trying to perform well and make you happy. And so you want to be vigilant of that and really make sure you're including each eye as you're testing monocular vision. And we do like to see vision in the range of 20, 20 to 20, 30 in this age range to be considered normal. So what if vision is abnormal by one of these testing modalities, what are you thinking about? Well, there's a wide differential diagnosis, as I'm sure you're aware, but some of the basic categories you could think about would be structural developmental abnormalities like a cataract, a coloboma, optic nerve, hypoplasia, trauma to the eye, infection in the eye, systemic disease. Another thing could be amblyopia, cortical visual impairment, delayed visual maturation, which is a diagnosis of exclusion. It certainly is an entity that we see where children just develop their ability for vision at a slower pace than others similar to other developmental delays, but you only make this diagnosis after you've ruled out every organic cause of vision loss. And always when you're starting to think that vision is abnormal, take into context your other interactions with the child outside of formal testing. So if the child's lethargic or inattentive, you're probably not getting an accurate visual assessment. If the child's playing a Game Boy or with other toys or their friends in the waiting area, but then they come into your exam room and can't read anything on the eye chart, take that into account as well and maybe just retest them at a different time. But I think the one thing we want to highlight in this particular lecture today is amblyopia as a form of vision loss. And this is in general caused by an abnormal visual experience early in life, two to four percent of children in the US at least will experience this form of vision loss. And it's responsible for more poor vision in children than all other causes of poor vision combined. And further, it's the leading cause of monocular poor vision in the working age adult population. And this is important because it's actually a preventable form of blindness. And so let's talk about how we can detect it and prevent it and or treat it if it's already developed. So you can see here that it's the diagnosis of amblyopia is when a patient is found to have a condition known to increase the risk of amblyopia or an amblyopia risk factor. And when you also see reduced visual acuity that cannot be explained entirely on the basis of an organic condition. And so you can see here in the classification scheme listed below, these are also the risk factors for amblyopia. So anisometropia where you have a difference in the refraction between the two eyes. You can also have bilateral amyotropic amblyopia where you have a high refractive error either myopia or hyperopia that will account for bilateral amblyopia. You can have a strabismic amblyopia where the misaligned eye is usually the eye with the weaker vision where you can have a deprivation amblyopia owing to corneal scar, cataract or some blockage of visual input to the back of the eye. So when we are diagnosing amblyopia, again, characteristics of vision alone cannot be used in and of itself to reliably differentiate amblyopia from other forms of vision loss. You have to use other techniques and other pieces of information. As we mentioned earlier, the crowding phenomenon can be helpful in doing this. If a child's visual acuity decreases, when crowding bars are placed around the image you're asking them to read, either the HOTV, the LIA images or the SNELL acuity chart. If their vision decreases with the crowding bars, that's suggestive of amblyopia. But it is not uniformly seen, so you can't, if they don't have that present, you can't absolutely say they don't have amblyopia. APDs or afferent pupillary defect can occur in severe forms of amblyopia, but it's not common in the more mild forms. And interestingly, amblyopia can coexist with actual organic disease, and so that makes it kind of difficult. For example, if a child has optic nerve hypoplasia, there may be visual potential in that eye. It won't be equal to an unaffected eye, but they can get amblyopia on top of their compromised vision from just the structural abnormality. And so these are things you kind of have to think about when following a child with an organic vision loss. And then you may need to do multiple assessments with a variety of testing to really sort out, particularly in a preverbal child. If they have an eye preference, if they're not using one eye or one eye is weaker at participating in your testing, sometimes you just need to do that on multiple occasions to really sort out what's going on. But the general principles of testing include looking at the fixation behavior in a preverbal child, as we've talked about, the different techniques for doing that. And then in a verbal child who can read the eye chart, looking at linear testing, utilizing the crowding bar phenomenon. Those are kind of the basic testing modalities we start with when we're thinking about amblyopia. And then when we think about the levels of amblyopia, essentially it's just mild, moderate, and severe. We don't have anything fancier to really talk about the levels. But you can see that there are criteria listed in the slide for the cutoffs for these. And then interestingly, we often see, not always, but often we'll see that refractive amblyopia is a more milder form. Strobismic amblyopia is often a more moderate form. And then deprivation amblyopia is often a more severe form. The reason for this is not quite clear. But, and it doesn't always follow this pattern. But in general, that's what we see. So when we treat amblyopia, there are a number of different treatments. But the first thing we think about is how can we remove the risk factor? So do they need glasses? Do they need eye alignment? Do they need cataract surgery? How is it possible to remove the risk factor that is causing the amblyopia in the first place? That's where we start. And then I always like to start with glasses if they're indicated. I always start with glasses if they're indicated in a child. Due to the fact that studies have shown children with amblyopia can have improvement of up to three lines of vision on the eye chart with glasses alone. And so if glasses alone, for example, for mild amblyopia, will entirely resolve the condition and the child wouldn't need more extensive therapy, it would be easier for all involved. And you would have resolved the amblyopia. So that's where I start. Now glasses are sometimes difficult to know when to prescribe, particularly in preverbal children. And we don't have any concrete guidelines or absolute cutoffs for prescribing glasses. If we see amblyopia, then we do prescribe if there's a refractive error. But there are kids that are at risk for amblyopia potentially due to their refractive error. But they don't manifest signs of amblyopia yet on the testing modalities we've talked about. So what do we do with those kids? Well, Sean, Donahue, and others, as you can see here, have done work to try and answer this question. And again, they're guidelines for prescribing. They're not absolute cutoffs. And I always consider these in connection with the exam that I'm getting from the child and how they're using their eyes. So it's one more piece of information you can use to assess the visual development of the child, the risk for amblyopia, and understand if they need an intervention and how to follow them. It's just one of the pieces in your toolbox. But you can see here that we won't go through all of them, but that at different ages, we would consider refraction over a certain amount to be an amblyopia risk factor. And so this is kind of a good thing to have in your office to refer to when you see these kids. So moving on to some of the more classic treatments for amblyopia, once it's been determined that the child has amblyopia, potentially the child's in glasses, but the amblyopia hasn't resolved, what do you do? Well, we have patching therapy, we have atropine penalization, we have optical occlusion. As you can see here, but the theme for all of these is that we're occluding the stronger eye so that the child uses the amblyopic or weaker eye. Amblyopia is fundamentally a decreased communication between the weaker eye and the brain because that eye's been disadvantaged because of strabismus, because of a cataract, because of a higher refractive error. That eye's disadvantaged, the developing brain doesn't want to tolerate a double image or a blurry image from one eye. So a developing brain can say, well, I'm just not gonna use this eye because I don't wanna tolerate this abnormal visual experience. And so we need to get the brain using that eye again. The way we do that is essentially to force it to use only that eye for a period of time. And so all of these modalities are based on that principle. The treatment overall is easier the younger the patient is as the patient becomes older because this is really brain training. The brain is developing and maturing and with that comes less ability to influence the brain's development. Just like in an adult the brain is fairly set. We can't do a lot to influence or change the brain's patterns. And so as a child gets older, the same becomes true. So traditionally we think that the age of visual maturity is about age eight to 10. So these therapies are much more effective earlier prior to that age. And as can be seen here, we've done a lot of testing on which modalities are best. And because I mentioned several to you all based on the same principle. And I think the take home is that overall studies have shown that two hours of patching a day as a starting point is equivalent to if you kind of extrapolate from all the studies is equivalent to, for example, starting with weakened atropine. A note is that atropine works by cycle-pleaging the eye that you've put it in, so the dominant eye. And that paralyzes accommodation, so it works most at near and it's gonna be most effective for that reason in hyperopes. It's relatively less effective. You could still try it in a myope, but just based on the principle by which it's working, it's gonna be less effective. So with that caveat in mind, overall we've done with the pediatric eye disease investigation group, PDIG has done quite a number of studies to really sort out what the best treatment is in terms of these occlusion therapies. And so the bottom line is we start with two hours of patching the dominant eye a day or weakened atropine in hyperopes. And that atropine is most effective if you administer it at night because it does two things. It dilates the pupil, but it also cycle-pleages. We don't really care about pupillary dilation. That's not what we need to achieve our goal. We need the cycle-plegia. And the cycle-plegia takes about 12 hours to get to full effect. And so if you put the drop in at night while the child sleeps, the cycle-plegia is taking effect and then will be in effect for the full day, the next day, and therefore that's the most effective way to administer that drop. The other important thing to note about the studies that PDIG has done is that children as highlighted here who are older than the traditional age of visual maturity into their teen years who have not patched before because it wasn't known that they had amblyopia. So they have no history of patching or atropine or any treatment. You can start the treatment at those later years and see benefit, particularly in the group that has never had patching or treatment in the past. So that's another important take home from these studies that PDIG has done. But I think that overall amblyopia treatment is a dynamic process. Every family and every child is different. And so you can see from the flow diagram here, which I think really well is a good exemplification of kind of the thought process we use in clinic. We might start with two hours of patching or weekend atropine, but then we have to assess how the child's responded if we need to increase our therapy, if their amblyopia has resolved, if they're non-compliant with therapy and that's why it's not working, maybe changing treatment modalities to fit the nature of the child's cooperation, the family's willingness to do the therapy, et cetera. And so it's not the same treatment for everyone and it's kind of a constant reevaluation depending on the things that you're measuring in clinic as far as how much improvement you're seeing, but also how compliant the patient and family can be with your treatment. And then these take home pearls I really liked from Dr. Wilson's book. I'll let you read those. They really are discussing the things we've already talked about, but his book has a full chapter on this topic of amblyopia and is very helpful in discussing our current knowledge, our current treatment modalities and can be of added benefit if you wanted something to read.