Lecture: Prescribing Prism for Diplopia in Neuro-Ophthalmic Disorders Part II

During this live webinar, we will continue to discuss the role of using prism to alleviate diplopia. We will briefly review the testing used to evaluate a diplopic patient. Next, we will use a step-wise approach to investigate the etiology of the double vision which will determine what type of prism to utilize. Prism for diplopia and visual field restriction will be discussed, including the advantages and disadvantages of both. Finally, cases will be used to illustrate how to prescribe prism for common neuro-ophthalmic and neurologic disorders including cranial nerve palsies, thyroid eye disease, and neuro-degenerative disease among others.

Lecturer: Dr. Kelsey Moody Mileski, OD, FAAO, Emory Eye Center, USA


DR MILESKI: Okay. Welcome, everybody. I am Dr. Kelsie Moody Mileski. I’m an optometrist and an assistant professor of ophthalmology at the Emory Eye Center. We’re going to do our part two lecture here on prescribing prism for diplopia and neuro-ophthalmic disorders. I have no financial disclosures. First I’m going to review what we talked about in our first lecture several months ago, just to kind of give a brief summary of how we do an examination for patients with diplopia and how we treat these patients. We’re going to be emphasizing differential diagnosis, how to monitor them, and what their workup may be. So the first thing we want to think about is: Is it monocular or binocular? Because that’s really going to change how we treat these patients. So symptoms that we first want to elicit is: Do the symptoms go away when either eye is covered? Some patients can have both, monocular and binocular double vision. Which can make things more challenging. We want to make sure we treat the monocular double vision first, and then we can have successful treatment of the binocular diplopia. Do the symptoms go away when one eye is covered? We’re going to think refractive error, cornea, lens, or retina. As a potential problem. We see this commonly in people with epiretinal membranes, potentially a bad cataract, or even high astigmatism can potentially cause monocular diplopia as well. But if it goes away when either eye is covered, then we know that we are likely dealing with binocular diplopia. Which our prism is going to be more successful with. So really our history is key to help differentiate this. We also want to do a couple other tests, to guide us towards what we think is going on. Which then can ultimately help with the treatment. So first we want to do a sensory test. This really helps me better understand what the patient is seeing. Specifically I like to do what’s called a Worth-Four-Dot test, and this helps me see: Is their double vision more present at distance or at near? And seeing how these dots split, depending on how we’re holding them. You can also do a stereo book test, but it’s going to be more beneficial at near. The other thing is to do motor testing, really looking at the eye movements, and doing a cover test or Maddox rod, which we’ll talk about. And you want to look: Is there any torsion. That can really help you differentiate between different conditions. This can be done with a double Maddox rod, looking to see how much the lines are rotating up and down to see if the eye is incyclotorted or excyclotorted. And then we’ll look at symmetry, look at exophthalmometry, lids, and pupils. This will really help with the differential. So after we look at eye movements, we want to check on our cover test. We can do both a unilateral and alternating cover test. A unilateral cover test is really gonna tell us the direction. Is the eye turning in? Which would be esotropia. Is it turning out? Which would be exotropia. Is it resting up, which would be hypertropia, or resting down, which is hypotropia. Oftentimes I call it a hypertropic eye, even if the problem eye could be a hypotropia. It just helps me differentiate patterns. We then also can determine if it’s gonna be a constant movement, or is it an intermittent movement? Which is really speaking more so towards the control. Which might give you a better idea of how they might respond to prism. We next want to move to our alternating cover test, where we’re gonna quickly jump back and forth between the two eyes. This is gonna give us the magnitude, which we’ll measure with prism, which will then give us an idea of what we want to prescribe. And then also we can look for those patterns, like we talked about. So going to our alternating, again, we’re gonna jump back and forth between the right and the left eye. And we’re gonna use our prism bar to measure this. So what a prism is — it’s a refracting surface that’s going to bend light. And the light is always going to bend towards the apex of the prism. So because of that, we always want to put the apex of the prism where the eye is resting. And so… Excuse me — if the patient has an esotropia, you want to put the base of the prism out, so that the apex is turning in, and the same thing holds true. Just the opposite for exotropia. You want to put the base in, so that the apex is resting out. And so this is true for both measuring the alignment and also prescribing for the misalignment. We had a lot of questions last time about yoked prism. Really with yoked prism, we’re going to put the prism in the same direction, in front of both eyes, to move the image, again, towards the apex. We’re always moving the image towards the apex. So similarly, if you put the base down, it’s gonna move the image up. If you put the base up, it’ll move the image down. If you put the base left, in front of both eyes, it’ll be base left. Base in, in front of one eye, base out, in front of the other eye, it will move the image to the right. And really, our goal with yoked prism is to move the image out of a defect. Move it out of a patient’s visual field defect, or move it out of an area where the patient can’t move their eyes. For instance, if a patient has progressive supranuclear palsy, and they can’t look down to see their food, you want to move everything down, so they can avoid that gaze. Also sometimes patients have significant nystagmus on downgaze or maybe leftgaze, and you want to move them out of that gaze. The only tricky thing with yoked prism is that you really have to give a lot of prism, to have any degree of movement. So in general, a 2 diopter prism shifts something by 1 degree, which is very minimal. In a pair of glasses, the maximal amount that we can put total would be 20. 10 in each eye. That’s only going to shift the field by 10 degrees, which isn’t going to functionally do much for a patient. We can do higher amounts with a Fresnel prism, but that is gonna create some blur and distortion. And because of that, it’s always better to put it sectorially on the lens instead of centered on the lens. When we talk about visual field loss, really the go-to is the EP prism. I put a link here that has a great guide about how to fit this lens. They’re two Fresnel prisms that you put above and below the visual axis, to try to make sure you don’t get image jump or a blurry or distorted area. The goal is to expand the peripheral field by 20 degrees using 40 diopters of prism, and to do that, you’re going to create intentional double vision, usually the opposite of what we’re trying to do. But you’re going to be creating double vision up and below the visual axis, that is going to get replicated in the patient’s normal field. So what they’re seeing here would initially be replicated in this area, but what will eventually happen is the brain will adapt with a lot of therapy, and hopefully it’ll actually appear in their blind field. So this really needs to be done with an occupational therapist, and this guide here will give you a lot more information on prescribing it. It’s not something I do often. But I did want to make sure we address it, since there were a lot of questions about this at our last lecture. So we have our patient in their chair. They’re complaining of true binocular double vision. We do the cover test on them. Now what? I want to focus at this time about ruling out the pathologic causes, and again, using our cover test to really kind of narrow down our differential. So when we have a patient with double vision, it’s really gonna be broken down into four areas. There’s either gonna be a problem with the brain, the cranial nerves, the neuromuscular junction, or the muscle itself. So let’s start with the brain, and so one common condition is called an internuclear ophthalmoplegia. We see this when we get a lesion with the MLF of the brain stem between the cranial nerve VI and cranial nerve III nucleus. Cranial nerve VI is lower in the pons. Cranial nerve III is gonna be in the midbrain. We’ll see this illustration we’ll use for the next few slides. This is the supranucleus in the pons, this is cranial nerve III up here. So you’ll see that VI — this would be the right eye, this would be the left eye — cranial nerve VI here is going to get stimulated and send it to the same side, for the eye to abduct. You can see that moving right here. And then it’s gonna cross over in the brain to the contralateral side. To the cranial nerve III. To cause the fellow eye to adduct. So this is to have a conjugate eye movement. So cranial nerve VI nucleus is actually considered the horizontal gaze center. It’s basically controlling this movement. And so in an internuclear ophthalmoplegia or INO, we get a lesion anywhere between this communicating pathway, and we most commonly see this in young patients who have multiple sclerosis or other demyelinating conditions or stroke in older patients. So if you have an older patient who presents and it looks like an INO, we really need to send these patients to the hospital for stroke workup. And the features, when you’re doing your ductions and cover tests are: You’re going to see an adduction deficit. The eye will not be able to turn in. Again, when you’re doing a conjugate gaze. When we’re looking to the right. The left eye won’t be able to turn all the way in. And because that’s happening, the brain is saying: Oh, I’m seeing double. It’s going to constantly then continue to send a signal to cranial nerve VI, to cause it to move to the right, and it’s going to get this nystagmus-like movement. So we’re trying to go in. The left eye can’t adduct. And the right eye is going to get this jerky movement, as it looks to the right, so that would be a very classic for an INO. So when the patient looks to the right, you should have a larger exodeviation, because the left eye can’t turn in. The next condition is going to be a gaze palsy. So it’s basically taking what we just said, but instead of lesioning between VI and III, you’re instead going to lesion the nucleus itself. You’re going to lesion the horizontal gaze center. So this condition is very difficult to miss. Because both eyes, when they go into a conjugate gaze, will not be able to move. In this condition right here, you can see that our patient can look normally to the right, but when they look towards the left, the right eye cannot adduct, and the left eye also cannot abduct. And this is always going to be ipsilateral to the lesion. So for this patient here, they cannot look fully to the left. It’s called a left gaze palsy. And so that would mean that our left cranial nerve VI nucleus has a lesion in it. Again, similar conditions we would think — demyelination in younger patients, and we would think stroke in older patients. The next is skew deviation, which is more of a complicated process. However, this can really occur in a very large area of the brain. Pretty much actually from the inner ear all throughout the brain stem. So it’s actually more common than we think. Again, stroke is probably the number one cause of this condition in older patients. And demyelination, again, would be more common in younger patients. The key to this is really to differentiate it from a cranial nerve VI palsy. We often think these are congenital or can be secondary to trauma. And again, this is gonna be another lesion in the MLF, and so it can happen in this very large area. And our cover test is really gonna give us a big cue to this. In addition to our double Maddox rod, when we’re looking for torsion. So you can see in this patient here — her left eye looks higher than her right eye. And then when she looks here, to the right, it looks maybe slightly better. But when she looks to the left, this is exaggerated even more. She has a much bigger left hypertropia, we could say. So it’s a left hyper, that increases on ipsilateral gaze. Left hyper is worse in left gaze. When we do the double Maddox rod, we occlude an eye, put a red lens in front of her, turn it until the lines look straight up and down and side to side. We see there is incyclotorsion, so the eye is turning in that’s higher. Another way is if you’re looking at the fundus, you might notice that the fundus is looking excyclorotated looking outwards. The next condition is called dorsal midbrain syndrome. This has a lot of other features. You would look to see what also looks different besides the eye movements. But here you can see that this patient actually is trying to look up here. So they typically have a vertical gaze palsy in both eyes. They may also have some problems with convergence. Because we’re affecting the dorsal part of the midbrain. Where our convergence center is. They may also have abnormal pupils, because our light near pathway is in that area as well. They could also have a skew, they could also have some of this nystagmus. So we’re definitely gonna be looking at other features here. Stroke is also again very common in older patients, but we can also think of neoplasms, because it’s at the back aspect of the midbrain, and hydrocephalus, because our cerebral aqueduct is around there as well. And we want to think about neurodegenerative disease. This might not be one of the main areas we’re gonna see on an MRI, but it is still is something that’s affecting the brain. We can see some things in the brain. With progressive supranuclear palsy, we can see some atrophy. But in Parkinson’s, we don’t see anything in this localizing area of the brain stem. Usually patients with Parkinson’s are gonna have convergence insufficiency, an exotropia that increases at near. They typically do best with two pairs of glasses, one for distance and one for reading, because the prism amounts are different. Another is supranuclear palsy — these patients might have some problems looking down, and here yoked prism can be attempted to improve their functional vision, when they’re trying to read potentially, or eat, because they have a hard time moving in that direction. Again, two pairs of glasses always for these patients. Next we’re gonna move on to problems with the nerve. And so the first is the cranial nerve III palsy. People always think about this as an eye that is down and out. Although that’s not typically always the case. There are actually two divisions. You could just have a superior division palsy, where this is affecting the lid. So they could have a ptosis, and potentially a problem moving the eye up, because the superior rectus is affected. Or there could be a problem with just the inferior division, where you get the inferior rectus, inferior oblique, medial rectus, and the pupil. The pattern we’re looking for in these patients is a reversing hyperdeviation. So for our patient here, the left eye is affected. You can see that here by his ptosis. And when the patient tries to look up, you can see that the right eye goes up. The left eye does not. So you have a right hypertropia. When the patient tries to look down, you can see the right eye moves normally. The left eye does not. So you can see that the left eye is higher, so now you have a left hypertropia. That’s what I mean by a reversing hyper. The hyper switches depending on when they’re looking. The patient then again — this is the left eye that has the problem. When he tries to adduct, the left eye cannot adduct. And so you can see an increasing exodeviation, as he looks away from the vertically limited eye. Increasing exo here when he tries to adduct. They often typically have diplopia at distance and near, because so many muscles are affected from this nerve palsy. And of course, always looking for the ptosis, because it does control the levator, and also looking at the pupil, where the pupil would be bigger, because again, it’s controlling those pupillary fibers. Next is a cranial nerve IV palsy. Again, very, very common here. Typically we see this congenital and traumatic. Although we can also just see congenital weakness. Which would go along with congenital causes, which we can then look for — increased vertical vergence ranges, a compensatory head tilt, not having any torsion when we’re trying to see if there’s any excyclotorsion here for a cranial nerve IV palsy. Here our pattern we’re looking for is different than a skew deviation. We’ll still have a hypertropia, because the superior oblique is affected, which is going to be — our superior oblique is a depressor when the eye is adducted. So for here, we’re going to have a hypertropia that’s going to get worse, when the eye is adducted. So in contralateral gaze, versus our skew deviation, was a hyper that got worse in ipsilateral gaze. This patient too will have worsening on ipsilateral head tilt. Versus contralateral head tilt is typically — they’re compensatory findings, when we’re looking at these patients. Next is a cranial nerve VI palsy, which is probably very common for people. This is the one we see probably the most often. It’s technically considered the most common oculomotor nerve palsy. Here we’ll have an esotropia that increases on ipsilateral gaze, where the patient is unable to adduct that eye. This can typically be isolated. It’s common we see vasculopathic cranial nerve VI palsies. But it’s also often the only neurologic sign in patients with raised intracranial pressure. So you should always look for this in patients with papilledema. Now we’re gonna talk about the muscle. Here we think about myasthenia gravis, although there are a couple of other rare conditions that can be seen here as well. Myasthenia gravis is an autoimmune condition that creates antibodies that either block, alter, or destroy the receptors for acetylcholine. We see this in a bimodal distribution. It affects young women or older men. They may have other associated signs if they have generalized myasthenia gravis, where they have difficulty breathing and swallowing, sometimes speech difficulties, generalized movement difficulties in their limbs and sometimes their lids. They can also only have ocular symptoms as well. We usually do bloodwork in these patients, to try to see if we can diagnose this. However, it’s typically only positive in about 50% of patients who actually have the condition. So just because your bloodwork comes back negative does not mean that the patient does not have myasthenia gravis. MuSK antibodies can sometimes increase that chance of coming back as a positivity. However, not always. And so sometimes if we have a high suspicion, we have to do a second test, which is called a single fiber EMG. Which really puts small acupuncture sized needles, like a regular EMG, in the patient’s forehead, and it can measure the orbicularis function. That can be very diagnostic for myasthenia gravis. And so there are some office tests that can help you, in addition to the double vision. Looking here at the lid specifically, you can have the patient look up for two minutes, and see if their ptosis worsens. If it does, then you can have them put ice on their lids, to see if again that brings the lid function back up. That should improve the ptosis. And if you have your patient squeeze their eyes really tight and try to manually open the lid, it should be very challenging to do it, although you might be able to. But if it opens very easily, that speaks to the orbicularis function being weak, which would also be a sign potentially of myasthenia gravis. Finally we’re gonna look at muscle, which is a little bit less specific. Although you can narrow it to the orbit a little bit more easily. So here you want to look at your exophthalmometry. You can potentially do a forced duction, where you want to manually move the eye into the position of gaze where they’re having a problem. If you’re unable to move the eye, that is considered positive, which would help you localize to the orbit. If you can move the eye, that would be normal and that would be negative, so that would speak to it potentially not being a problem with the muscle or in the surrounding orbit itself. They may also have other symptoms like eye pain or conjunctival injection, chemosis, or potentially even an optic neuropathy, something physically pushing on the nerve itself. We can think of something being in the eye, on the muscle, but other signs of inflammation can cause similar things. We see this commonly in idiopathic orbital inflammation, where we can have this almost inflammatory mass effect that can cause motility restrictions. Now, I think I had this on my last lecture. This is for you to potentially look at later. This is kind of a graphical illustration of how we go along in differentiating these types of double vision in these patients. And then for treating, this is again a review from last lecture. We can think about really three options in the acute stage of double vision. Either a type of prism or occlusion. For Fresnel prism, we can do this right in the office, press it on the patient’s glass, so they can get immediate relief, potentially. We can use this as we’re working the patients up, use it as temporary relief, or even permanent relief if they need higher amounts, because with Fresnel prism, we can go up to really high prism amounts. Whereas ground-in prism is more if it’s stable, and it’s better cosmetically, because you can’t see it in the glass, but it’s something we don’t want to do right away. And occlusion is an option. Sometimes patients’ vision is very non-comitant and they’re not gonna do that well with prism because if they move their eye slightly in any direction, the diplopia comes right back. So occlusion can be a better option for some people, and we’ll talk more about that later. So we’re doing good here on time. Let’s move on to our cases. Case one. So we have a 76-year-old man who presents with blurry vision in his right eye more than his left eye for the last six months, but he’s also noticed some new diplopia in the last six weeks. He’s noticed that it’s intermittent, vertical, only noticed it in the car, and only for the last week to a few days. When we look at our testing here, we’re looking for symmetry. The vision is about the same. Color vision is normal. Pupils appear isocoric. There’s no APD, pressures are equal. But he is proptotic in the right eye here more than the left eye. When we look at his motility, we can see here… That the right eye has a small supraduction deficit. It’s hard to move the eye up. And a more noticeable infraduction deficit. When we do Worth-Four-Dot, we see he has diplopia as well. He’s seeing 5 dots. When we look at the cover test pattern, we see he has a hypertropia that does actually reverse. When he looks down, he has a right hypertropia. That makes sense. He has a hard time looking down. And when he looks up, he has a left hypertropia, which makes sense. He has a hard time moving the eye up. He also has an exophoric posture that’s hard on up and down gaze, but otherwise comitant when you look across. We have a hard time testing him. Because of the proptosis, maybe there’s an issue that we could localize to the orbit. But we see a very homonymous defect — and this matches on the other side, a left hemianopia. Overall this looks fairly normal, but now what? What do we want to do? He has double vision. We want to give him some treatment to make him more comfortable, but he definitely needs more testing. We want to get him an MRI of the orbit and the brain. Because he has two different things going on here. Fortunately he has an oncologist, and his oncology team had already ordered this test. And this patient, with his eye findings, you could potentially do a CT of the orbit, but he also has that visual field defect, so because of that an MRI would be a better test for him. He does have a history of kidney disease and kidney cancer. I don’t think I included that in his first slide. We want to make sure the kidney function is okay so he can get contrast dye. That’ll give us more information. So we want to treat his dry eye, and hold off on his cataracts, until then. So here was his MRI. So you can see this lesion affecting the right inferior rectus muscle. Which was causing his supraduction deficit and his infraduction deficit. Because when he was trying to look down, he was basically looking into this mass lesion. And he also has this large occipital lobe lesion here as well. Which was causing his visual field defect. So he was sent back to his oncologist, because there was concern that this was metastatic disease. We also consulted oculoplastics to make sure there was no surgical indication for that problem with the muscle itself. And we needed to get him some glasses, before we could even do anything with prism, because he didn’t have anything. For this patient, he had something acute going on. And so we didn’t want to give him permanent prism. Because we didn’t know how it was going to change. So we really gave him glasses that were single vision distance and single vision reading. Because of the difference in his alignment. So that we could apply some temporary prism to it. Excuse me. So he came back for his two month follow-up. He had completed radiation to both the brain and the orbit. And no surgical intervention had been done at this point. So again, everything here looks symmetric. Similar to our last exam. But his motility findings actually do look quite a bit better. Supraduction looks normal. He has a small right hyper, but it’s minimal. But infraduction also looks better here as well. So overall, alignment looks better, although some misalignment still is remaining. His visual field defect has resolved since radiation, which is wonderful. But he does still have some symptoms of diplopia, particularly at distance. With his distance pair of glasses, we fit him with a four base down Fresnel prism, because we want to make sure this is stable, and he found if he held his reading material higher and took him out of his limitation when he looks down in his right eye, he didn’t have any double vision at all, so we didn’t do any prism on that. We wanted to treat ocular surface, eliminate any monocular component to his double vision with tears, and because of his comorbid conditions, and the fact that this might be… Might change… We were holding off on any surgical intervention for strabismus surgery. So here is our first poll. What is true about a Fresnel prism? It is placed on both eyes, it’s good for temporary or permanent treatment, it’s not visible on glasses, and it only comes up to 20 prism diopters in power. Which of these is true? About Fresnel prisms? All right. Great. A majority of people got this right. Good for temporary or permanent treatment. So this is good for higher amounts of prism that we can’t do with ground-in glasses. A 30 or 40 diopter. We can use it for both purposes. We typically only put it in front of one eye, because it’s visible on the glass, and it can go up to, like I said, higher amounts. So for this patient, this is just a summary of what we talked about before. We could localize to the orbit because he had proptosis. We didn’t do forced ductions on him because his misalignment was not that large. It would be hard to see that change. He didn’t have any symptoms of eye pain, but he had asymmetric dry eye, with a little bit of injection. But fortunately that mass along the inferior rectus was very close to the optic nerve. But it did not push up against it. He did not have an associated optic neuropathy. When we’re thinking about common orbital problems, probably the most common thing we see is an orbital fracture. Typically in these patients, they can have a supra or infraduction deficit, particularly if the front or back of the floor is fractured. They might also have hypoesthesia. Sometimes we observe these patients and see how they change with time before surgery is pursued, depending on how bad the fracture is. Sometimes surgery is needed right away, so you need to coordinate with your oculoplastics team, potentially ENT, or a surgeon for these patients. Thyroid eye disease is seen commonly. They might have an abduction deficit. We can also see eyelid retraction in these patients, and periorbital edema. A CT orbit could be a good study for these patients. Other things to think about, especially if things are more acute would be a mass, a mucocele from the sinuses, if they have a past history of sinus surgery, lymphoma can sometimes be painless, slow progression. Or metastasis like our patient. Also always think about inflammatory conditions as well. Especially if there’s a rapid diplopia, rapid pain, chemosis, redness, injection. You would always want to think something potentially inflammatory could be going on. Workup. Again, we’re gonna think about neuroimaging. Oftentimes CT can be done fairly quickly if we think something is primarily in the orbit. However, if something is more — we’re thinking something is more tissue, something more like cancer, an MRI can sometimes help differentiate these etiologies. Bloodwork may be helpful for some conditions, like thyroid problems or inflammatory conditions. And oftentimes we do need to co-manage these patients with our oculoplastics team. However, it’s always important, like I said, to treat their double vision potentially with some Fresnel prism until they become stable, and treating other ocular comorbidities like dry eye in our patient. Okay. We’re gonna move on to case two. So here we have a 55-year-old female who has double vision and headaches. She says the double vision started three days ago while driving and it’s been constant. She also has some mild blurry vision in the eye and headache, history of diabetes, high blood pressure, asthma, and some dry eye. She takes medication for all of those things. She also has a past surgical history of a spinal stimulator, hemorrhoidectomy, and a C section, and has some allergies to medications. So we’re gonna look for symmetry. Vision is fairly normal. Color vision is equal. However, when we look at her pupils, we can see that there is a difference here in her pupillary size. And when we go over here to her motility, you can see that she has a supra and an infra-adduction deficit and also a very mild adduction deficit in the left eye as well. I believe I switched the pupils here, where I said sluggish — now that I’m looking at it — you can see the right pupil, there’s a bigger difference between bright and dim illumination, about 1.25, and the left pupil doesn’t get as small as the right pupil in bright. So it should say there’s a sluggish reaction here in the left pupil and more of a brisk in the right. That’s why there’s a pupil abnormality in the left eye. So here our patient’s cover tests. We have a problem with the movement of the left eye, and we can see when the patient in primary gaze — the left eye is sitting a little bit lower, we have a right hyper. When they look up, we still have a right hyper, and when they look down, it switches. We have a left hyper. We have an exotropia that’s fairly equal on up and down gaze. A little bit less in left gaze and a little bit greater when the patient looks in right gaze. So here we have this woman. She has diplopia and headache. What is our diagnosis and our differential? So we know we have an exo, and we have a hyper. So we want to think: Is it a cranial nerve III? Cranial nerve III palsy, cranial nerve IV palsy, INO, skew, myasthenia gravis — myasthenia gravis can look like anything — or could it be a problem with the orbit? And because of her age, we always do need to think about giant cell arteritis as well. Our other findings, though, that can help narrow our differential is: She has a ptosis in the left eye, anisocoria, with the left pupil not getting as small as it would normally, and double vision. She has no proptosis or pain, so it’s probably not a problem in the orbit itself. What would our workup be for this woman and what would her treatment be? Really for her, we have to be most concerned for a cranial nerve III palsy based on that pattern. She had increasing exo as she adducted that eye, and had a problem with the pupil and the lids, so all of these things are pointing towards cranial nerve III. So she really needs a CT of the head to rule out aneurysm and MRI of the brain and orbit with and without contrast. Pending neuroimaging, we can think about myasthenia gravis as well because of the ptosis. However, the pupil would be abnormal. Typically the pupil is not affected in myasthenia gravis. For her, because her misalignment was so non-comitant, we recommended patching her left eye. With her ptosis, it kind of worked out, because her ptosis was occasionally covering the eye as well. For her, interestingly, her neuroimaging was normal. So now what do we do? So we see her back a month later. We see that her alignment looks better. She still has a hyper, but it’s much smaller. She still has that exo, but much smaller than what we measured previously, and we see her a month later and her alignment is nearly normal. 2 exophoria in primary gaze, which most patients don’t have symptoms for, so we don’t have to give her a prism at this point, because she’s doing so well. We think about cranial nerve III palsies — as we mentioned earlier, we know that cranial nerve III starts in the midbrain. This includes the vertical gaze center, issues with the midbrain, the light near pathway, contralateral motor fibers, contralateral sensation. So we can test these things to differentiate if we have a lesion within our midbrain itself. Cranial nerve III is going to exit the midbrain ventrally, course through the subarachnoid space, and it’s here that we can have a PCOM aneurysm that can push on the cranial nerve. It’s going to enter the cavernous sinus, where we can have multiple cranial nerve palsies, and then it enters the orbital apex, where we can have multiple cranial nerve palsies and an optic neuropathy as well. We know the cranial nerve III is going to bring the eye up, down, and in, and also potentially extorsion. The most common cause of cranial nerve III palsy is ischemic. Vasculopathic. Aneurysm and tumor are high enough that we always have to work up these patients, though. There’s always a question of: Can we use the pupil as a guide to tell us if there’s high suspicion for a mass or an aneurysm for the nerve? So we know that if the pupil is involved, that compressive lesions need to be ruled out. Because the pupillary fibers around the — in the cranial nerve — run on the outside of the nerve. And so if something is going to be pushing on it, the pupillary fibers are probably gonna be affected first. Whereas the blood vessels supply the inner area of the nerve and work out. So if there’s an ischemic cause, potentially those pupillary fibers may be spared. However, we really always still recommend neuroimaging in these patients, because sometimes the pupil findings can be very, very subtle, or can happen a little bit later. And so we still usually recommend ruling out an aneurysm and a mass, with a CTA and MRA and MRI. Also in elderly patients we always need to think about giant cell arteritis. Thinking about those vascular causes. If we think about inflammation as well, of the blood vessels, it can cause something very, very similar. So we might always want to think about ordering inflammatory markers to rule this out. And again, if things don’t add up, always think about myasthenia. Treatment for these patients — because they typically have an exotropia and hypertropia, it’s typically very non-comitant, depending on where they’re looking. We can try to do prism, but really our goal is gonna be straight ahead and down for reading. Primary gaze only if we’re gonna be doing prism. Oftentimes Fresnel first if we don’t know the etiology. But oftentimes, sometimes, patching and occlusion can be better. If the patient has a big pupil, sometimes they respond really well, actually, to an occlusion contact lens. It also may not be visible if you just make the occlusion the size of the pupil, because often they’re light sensitive with that pupil being so big. Also fogging them with a contact lens can work as well. And sometimes these patients a year out can be great candidates for strabismus surgery, but again, we want to wait the full course to see if they improve or their deviation changes. Okay. Our next poll here. So what is not true about the cover test pattern for a cranial nerve III palsy? Not true. So a hypertropia that changes on up and down gaze… An exotropia on adduction or an esotropia on abduction. So what is not true about the cover test pattern here? All right. The majority of people got it correct. What’s not true is an esotropia on abduction. Otherwise we do see an exotropia on adduction, because the medial rectus could be affected, and we also see that reversing hyper, because the superior rectus and the inferior rectus are both affected. All right. Case number three here. So we have a 43-year-old female who has double vision and dizziness. She’s been noticing double vision for the last week. She describes it as initially her left eye was starting to drift out, which people were noticing, and she noticed she was seeing double and her vision was very blurry. She states it resolves if she covers her eye. People said her speech seems off. She has a history of myopia and wears contact lenses. Systemically, she has von Willebrand’s disease, we can think clotting, potentially, hypothyroidism, so we can think thyroid eye disease, and she has no past history of surgery. Again, we’re looking for symmetry here. Everything looks fairly equal. When we look at her motility, she does have a right and left very mild adduction deficit. When we do the cover test here, we can see she’s esophoric in primary gaze, exophoria in left gaze. When we look at motility, we can see jerky movements in each eye when she looks to the right and to the left. We have this abducting nystagmus on right and left gaze. Also when she looks up, she gets a little bit of an upbeat nystagmus. In upgaze as well. So here what is our diagnosis and our differential? For her, she has bilateral adduction deficits. She also has… I guess I probably didn’t put it on here. She has a hard time moving her eyes up. She has a little bit of a vertical gaze limitation. And she also has jerkiness when she tries to look up. She has a little bit of nystagmus. Here we have to think brain. As soon as we think nystagmus, you should think brain. Really you want to think about: Is it an INO? Skew? Bilateral III? But again, we know she needs neuroimaging because this is localizing to the brain with that nystagmus. We get an MRI of the brain for her with and without contrast. We didn’t get orbits, because we’re thinking brain. Right now, we recommend occlusion, because her deviation is non-comitant. But also that nystagmus can really make fusion a little bit more difficult. So for her, right now, I put a Bangerter filter for her on her glasses, for an occlusion effect to the eye while still keeping her comfortable. Here is an MRI. You can see on the axial flair that there’s a large enhancing lesion in the midbrain, and you can see it in the sagittal scan as well. It was thought that this was inflammatory. So she was treated with IV steroids, and her ocular symptoms improved. At her two-week follow-up, her alignment was fairly normal. And she just had very subtle upbeat nystagmus on upgaze. And gaze evoked nystagmus on left and right gaze. However, really in primary gaze and downgaze she was very comfortable, and did not require any prism. So this patient actually had an INO and a skew deviation. Because these things commonly occur together, because they’re both affecting the MLF. And again, we always want to think MS or other demyelinating conditions in young patients and stroke in older patients. This patient had a demyelinating condition that they didn’t think was specific for MS. However, it was being treated more as an autoimmune inflammatory condition. And here neuroimaging is always going to be key. We often need co-management with neurology, because they may need immunosuppressives or immunomodulating therapies. And they may or may not improve or resolve, depending on what’s causing it. So we can always treat with Fresnel prism as we’re watching these patients, or potentially occlusion. So here is our third poll. True or false. Abducting nystagmus occurs due to overstimulation of the contralateral cranial nerve VI nucleus. True. Good. Reading the question back, I might have made it somewhat confusing by writing contralateral. But we get abducting nystagmus because cranial nerve III can’t get the signal. It keeps sending a signal contralateral to the cranial nerve III — cranial nucleus of VI, to try to get this movement. It’s not a true nystagmus, because it’s only happening in one eye. And it’s happening basically to try to prevent diplopia. This is our final case. And we’ll go to questions. So we have a 68-year-old man who has double vision. He said it’s been present for a really long time. Over 60 to 65 years. Actually, that doesn’t make any sense. But he’s noticed it since 1957, secondary to trauma. He was hit by a car. He said it’s always been intermittent, though. But recently, now, he’s noticed that it’s occurring more often. It’s increased in frequency. He’s noticed maybe that it’s worse when it’s tired or when he’s driving at night. He noticed that sometimes it’s vertical, sometimes it’s horizontal, and sometimes it’s torsional. So the question right here: Are we talking about one thing from trauma, or are we talking about multiple things, potentially? Systemically, he has a history of anxiety, BPH, coronary artery disease, depression, high blood pressure, high cholesterol, stroke, and this remote history of head trauma when he was in a car accident as a child. He takes medications for the above and does note some social alcohol use. So again, here, we’re looking for symmetry. Everything looks fairly normal. When we look at his motility, we can see he has this fairly comitant exophoria and hyper. The left hyper does increase slightly on downgaze, but it really doesn’t help us differentiate if it’s on ipsilateral or contralateral gaze what this could potentially be. So if we think about our diagnosis and our differential, it could be a cranial nerve IV palsy. Maybe it’s congenital. That’s why it doesn’t look like it has a specific pattern. But we do also want to think about a cranial nerve III palsy, because he does have an exophoria and a hypertropia. He does have this history of trauma. Could there be a problem with the muscle itself or the orbit? Myasthenia gravis, because it can look like anything. And it’s changing direction. Or is it just a decompensated phoria? Some pertinent findings. It is longstanding. However, he notes that it’s worse when he’s tired and it changes direction. Although I will say sometimes patients are not accurate with the changing direction. Sometimes it’s hard for them to elicit what the double vision truly looks like. However, he doesn’t have any other neurologic or localizing signs and symptoms, which is somewhat reassuring. What do we do for this patient? We still recommend an MRI. We really don’t know what’s causing this. Specifically the fact that it’s been increasing in frequency. Also some bloodwork, looking for thyroid conditions, myasthenia gravis, but he is symptomatic, so we did fit him with a 3 base down prism over his right eye, and he did have fusion in the exam room. So he got all of the testing and really everything was pretty unremarkable. MRI was normal, bloodwork was normal, and the Fresnel prism he notes works sometimes. But not always. So now what do we do? So for this patient, because his double vision was fluctuating, we did get a single fiber EMG, which was positive. So this was consistent with myasthenia gravis. So probably his remote history of double vision as a child was very different than what he was noticing now. And so myasthenia gravis should be a differential on any patient. Who has double vision or ptosis. It can look like anything. It can look like a cranial nerve VI palsy. It can look like a skew deviation. It can look like a cranial nerve III palsy. So we always want to think about it. Always ask about a history of eyelid surgery in these patients. Sometimes they have a history of ptosis and they actually already had blepharoplasty, and maybe that’s why their lids look somewhat normal to you at that time. Always ask about fatigability, is it worse at the end of the day, and decompensated phorias are also worse at the end of the day, so that’s not a specific finding. Ask about change in direction and other generalized symptoms of myasthenia as well. The workup, like we said before, the bloodwork can be negative in 50% of patients who only have ocular symptoms, and if that’s the case, we always want to consider getting the single fiber EMG, which can typically be done with neurology. And in these patients who are positive, they need a chest CT to rule out thymoma, because that could be a treatment for patients with myasthenia gravis if they have one. You can refer to neurologist or neuroimmunologist. They can be started on immunosuppressive medication, you should educate on symptoms of myasthenic crisis, which should send them to the hospital if they have difficulty breathing, and you can try prism, but oftentimes the misalignment is not stable. I recommend that they start on medications first to see if that resolves the double vision first, or if there’s a residual misalignment. I’ll try to give them Fresnel and see if it stays stable. If it fluctuates too much, we really want to think about types of occlusion. So here is our final question. What are different options for occlusion? A Bangerter foil or frosting of a glass? An eye patch, a pupil blocking contact lens, a high plus contact lens, or all of the above. Okay. All of the above. A Bangerter foil — typically I get light perception or 20/400. That can be ordered online. You cut it to fit the glass and it typically creates enough blur to the patient — so either light perception or 20/400, that they can ignore the other image, but they can still get light to the eye and around the eye to the glass. It can make them feel more comfortable. If they like that, they can get the glass frosted, which can create a similar effect. An eye patch can also work, but it sometimes causes itchiness if they put it on the skin itself. They can also get one for their glasses. I like doing things with contact lenses, because it’s less cosmetically noticeable for patients. You can get one that’s black in the center that can block the pupil. This is great for cranial nerve III palsies, or if you want to get light to the eye, you can do a high plus lens to create that blur effect, which can really be nice for some patients. So some clinical pearls. Any patient with double vision — you always want to check motility, get a sensory test, and your motor test is going to be your cover test with your Maddox rod to evaluate for those patterns, figure out how big the misalignment is, so you can give them prism. You want to evaluate if the double vision is isolated or they had any neurologic or ocular signs and symptoms that can help narrow down your differential diagnosis. You should consider workup in all of these patients with acute double vision. Or even chronic double vision that’s changing with neuroimaging. Potentially bloodwork. And refer to the appropriate subspecialty, depending on your testing. And treatment — prism can be a wonderful thing, that can really improve patients’ quality of life. Oftentimes I see patients who were told that nothing can be done besides surgery, and really, there’s a lot of different options we can do with prism and even occlusion, because it can really, really make them more comfortable if they’re not seeing double. Here are my references. And now I’m gonna stop my share so I can answer some questions. All right. Our first question here. What is intranuclear ophthalmoplegia? That is where we get the lesion in the brain stem between cranial nerve VI and cranial nerve III. So now the nerves can’t talk for our conjugate eye movements. And moving the eyes to the right and moving the eyes to the left. So because we get a lesion in between, we’re going to have an adduction deficit, because cranial nerve III can’t get the stimulus from VI to create that conjugate movement. You mentioned that when double Maddox rod is done, you occlude one eye. Any specific reason? It’s to get the torsion. You’ll see the torsion regardless. But you occlude the eye to make the patient understand it. How much Fresnel prism is beneficial for hemianopic and nystagmus? I don’t have typically good success with yoked prism. I show it to patients to see what they think. But the amount you have to give them is typically 40 prism diopters to get it to move, which is gonna get it to move to 20. The Eli-Pelli prism is typically used most commonly for hemianopic fields, and those are typically placed on the glass. I attached the guide to Chadwick Optical for the fitting instructions. This really needs to be done with an occupational therapist because it takes a lot of practice to use the lens properly. You can use prism sectorially for Fresnel, or ground-in for reading. I wouldn’t recommend that for patients who are walking. Because they’re gonna get a lot of image jump and everything is going to be shifted. What is the range of Fresnel prism that can be prescribed? There’s as low as a 1 and as high as a 40. So on the smaller numbers, it goes up by 1. So from 1 to 10, it goes up by 1 prism diopter. After 10, it goes from 10, 12, 15, and then 20. 25, 30, 35, and 40. Once we get to the higher numbers, it can be a little bit more challenging, if your patient is in between numbers. And also if they have a vertical deviation, sometimes you have to actually rotate the prism to try to get a net effect. And there are actually computer calculations that you can use online, to help you determine what that vector could be. How long can prisms be worn? They can be worn for your whole entire life. Often for patients who get fit in prism, we can see it changes just like the glasses prescription. Sometimes they need more and more. I usually always bring new prism patients back in 6 to 8 weeks, because sometimes when I give them prism for the first time, they can kind of adjust to it, and need a slightly more than what I prescribed. It’s usually not less. It’s usually a little bit more. And then I can always give them a glasses remake. And most opticals will honor that and let me change it without charging the patient. That can be really nice for patients. But typically they’re worn for most of their life unless they get strabismus surgery, which can be a good option for people. Last time we talked about who is a good candidate for strabismus surgery. It will be patients with a longstanding deviation, at least a year, that’s stable. And a large alignment. Misalignment. So typically for patients with horizontal problems, so eso or exo, we typically like it to be greater than 10 prism diopters, and for hypers, typically greater than 6. Usually they’ll have a better response to surgery. I had a patient with a 40 diopter esotropia from trauma. We waited a full year and she is now orthophoric in primary gaze and does not need prism. But we had to give her prism for a year to get her comfortable until she was a candidate for surgery. So expansion prism… Is it suitable for gaze palsy or one and a half syndrome? Gaze palsies typically I don’t give prism for. I wouldn’t give it early on again in the acute phase for a patient with a gaze palsy to avoid that gaze. Potentially if they had it longstanding maybe you could give them a yoked prism. But it really depends on how much their eye is not moving. Is it not going past midline? That patient I showed you — it was going pretty far to the side, and I probably wouldn’t consider it for them. In some patients, I think it’s something that could be considered. For one and a half syndrome, probably not. Because they would actually be diplopic in primary gaze. You have the adduction deficit in one eye. But it’s just to the left that it looks funny. Or the right, depending on which side it is. Can noncomitants be provided with head scanning or training? So if their deviation is non-comitant, my goal is to get them to have fusion in primary gaze. If the patient is okay with that, and I definitely have a lot of patients who are completely fine with being single in primary gaze and knowing they have to turn their head to avoid that gaze. So yes, I always try to give them prism. My goal for them is to always have binocular double vision. But sometimes some patients are just so sensitive to any small eye movements, and even when we try prism, they’re just too uncomfortable. And that’s when we go to occlusion. But I always try prism first, in the exam room, and I always see if they’ll be willing to try it at home. And there are just some patients who really can’t tolerate the misalignment when they look in different positions. But that would be ideal. Is there any indication for Fresnel for temporary use? Yes. My number one reason for Fresnel for temporary use is vasculopathic cranial nerve palsies. Typically they’ll improve, I’ll usually see them back maybe once a month, four to six weeks, to see if their prism needs to be changed, or sometimes they even notice that their prism no longer works. And that’s a sign that maybe it’s getting a little bit better and then we’ll switch out the prism. So occlusion is basically gonna be covering an eye, and it can be done with physically blocking the eye, with an eye patch, or just making one eye blurry. If we make one eye blurry, the brain will naturally try to ignore that diplopic image. Is it possible MG starts so early and can become stable? I have very few patients who become stable with myasthenia gravis and still have a little bit of an ocular misalignment that does not change. I have one patient who actually ended up getting surgery and another patient we’ve done prism on, and is pretty successful. But sometimes they have to balance out the medications first before we start to think about doing that. And so I usually like to… I’ll give them prism again to try it. But always Fresnel. If it’s too variable, we do occlusion and they become stable on medications and we reassess. In midbrain, is there convergent spasm or convergent palsy? They can have either or both. It can be a very variable presentation. They can have a hard time converging because of the light pathway, but when they try to converge, they can have a spasm and go up. Different from convergence spasm — they can have convergence excess — that’s a bit different. Can patches be enough? It can be sometimes. It depends on the patient. It’s something you can try. I know a lot of people do like to try that option. Binocular vision management. Do ophthalmologists do vision therapy for strabismus patients? It depends on where you practice. Sometimes they do it for convergence insufficiency but don’t typically do it in adult patients with other types of strabismus, but it’s very dependent on your area. The most cost effective treatment is going to be the Fresnel lens. Or occlusion. Occlusion is probably the cheapest, because you could put tape on your glasses, even, and that would occlude a lens. But a Fresnel prism is also pretty cheap. It’s about $25. I think we discussed double Maddox rod already earlier. What is the MLF? The medial longitudinal fasciculus. It’s basically the area where the eyes communicate. It runs all throughout the brain stem. It has a lot of different functions and can do a lot of different things, depending on how the eyes communicate with each other. But it’s gonna be that communication between both eyes. How to manage torsional diplopia? Great question. It can be really challenging. Oftentimes when we treat the horizontal and the vertical misalignment, we can usually make most of the torsion go away. I have a couple patients, though, very few, where they still have a hard time fusing, because of torsion. I think you can always consider a strabismus eval, just to see if there’s anything they can do in terms of moving the muscle itself. But that’s actually quite challenging. Especially if it’s truly binocular. Sometimes it has a monocular component. So I will say a lot of patients I’ve had have also had a monocular component to the torsion. Again, make sure you’re always treating that first. Do the apps on phone help to explore the gaze? I’ll see if I can pull it up. I actually have a wonderful app that really more so can help document your patients. I don’t think it’s on my phone. It’s on my iPad. I’ll see if I can send a follow-up email with it. Or you can email me after. I can see if I can share it. There is a wonderful app that you could get, that could help… Let me see if I have it on here. Take a look at the eye movements. You can take a picture of — and you can look at the picture in all different gaze, to try to tell the misalignment. I like it better for documenting it in the patient’s chart to compare it to the next visit. But there is a really good app. I’ll have to find it, though. Please do tutorial for these tests like exophthalmometry. I would love to go into detail on these tests. But you have to have an exophthalmometer to do it appropriately. People who have diplopia that’s different at distance and near — always two pairs of glasses. I’m a big proponent in general to do two pairs of glasses. Especially in patients who have neurologic disease. If your patient has neurologic disease and you put them in a progressive, they’re gonna be uncomfortable. I always typically recommend two pairs of glasses in these patients. One for distance, one for reading. They can use the whole lens. It won’t affect their balance or their gait, and typically they do so much better. It’s typically inconvenient in the beginning, but most patients adapt quite well to it. I’m gonna take one more question. How to manage ptosis. That’s a good question. So ptosis typically is specifically for cranial nerve III palsies. We watch in the beginning. But sometimes we’ll also need surgical intervention. Oftentimes I believe our surgeons do the lid first, and then we determine if we want to do prism on the patient for diplopia, or if they want to get strabismus surgery. But typically, if we don’t see improvement in the lid in the first few months, then they do typically get surgery to improve it. You can also think about an eyelid crutch with glasses. The problem with eyelid crutches with glasses is that the patient dries out because their lid is staying open. So oftentimes we consider surgery in these patients first and do the double vision after. So usually I see them pretty soon after, because they’re usually diplopic. Those are gonna be my questions for now. We’ll take these into account to see if we can do more in the future. Thank you for your attendance and have a good rest of your day. Bye-bye.

Download Slides


Click here to watch Prescribing Prism for Diplopia in Neuro-Ophthalmic Disorders Part I

November 4, 2020

Last Updated: October 31, 2022

5 thoughts on “Lecture: Prescribing Prism for Diplopia in Neuro-Ophthalmic Disorders Part II”

  1. very informative lectures. Generally how many times a patient generally have to change the prism prescriptions before being stable?[ It is important to counsel patients regarding the costs of prisms]
    i) For isolated 6th nerve palsy
    ii) For isolated 3rd nerve palsy. (do you incorporate lid crutches as well?)
    is it better to give trial of prism after 6 months of these palsies?

    Thank you.

    • 1. If I think I need to change out the prism then I always do Fresnel to limit the cost for the patient. I typically bring them back in 4-6 week intervals. If they notice a difference sooner than that then I have them call me and bring them back in sooner. The amount of times is quiet variable – it could be one or five (usually only 1-3 times on average I’d say)

      2. I don’t typically use an eyelid crutch because then they can’t typically blink at all unless they have a great Bell’s reflex and then they just get severe dryness. It also typically helps resolve their diplopia temporarily until the lid comes up. If it does not, then I refer for ptosis surgery first and then we deal with the diplopia (whether it be with prism or surgery or occlusion (I have used CL’s here with success due to photophobia from the larger pupil)

  2. very informative lecture. thank you.
    question : can we give horizontal prism to one eye & vertical prism to other eye to overcome vertical+horizontal diplopia. eg. 2^ BD on OD & 6^BI OS.
    please send me the app you told about record keeping. thank you.

    • Yes you can do this. You can also combine in the same lens. In your example provided, I would typically write this out as:

      OD: 1 BD and 3 BI
      OS: 1 BU and 3 BI

      This way the lenses will look symmetric.

      The app is called 9 Gaze.


Leave a Comment