Approach to Diplopia With Dr. Devin Mackay

Double vision is a symptom often experienced by patients with neurologic disease. An organized systematic approach to evaluating patients with diplopia needs a foundational understanding of the neuroanatomy and examination of eye movements and ocular alignment.

In this episode, Teshamae Monteith, MD, FAAN, speaks with Devin Mackay, MD, FAAN, author of the article “Approach to Diplopia” in the Continuum® April 2025 Neuro-ophthalmology issue.

Dr. Monteith is the associate editor of Continuum® Audio and an associate professor of clinical neurology at the University of Miami Miller School of Medicine in Miami, Florida.

Dr. Mackay is an associate professor of neurology, ophthalmology, and clinical neurosurgery at Indiana University School of Medicine in Indianapolis, Indiana.

Additional Resources

Read the article: Approach to Diplopia

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Full episode transcript available here

Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast.

Dr Monteith: This is Dr Teshamae Monteith. Today I'm interviewing Dr Devin Mackay about his article on approach to diplopia, which appears in the April 2025 Continuum issue on neuro-ophthalmology. Welcome to the podcast. How are you?

Dr Mackay: Thank you. It's great to be here.

Dr Monteith: Congratulations on your article.

Dr Mackay: Thank you. I appreciate that.

Dr Monteith: Why don't you start off with introducing yourself to our audience?

Dr Mackay: So, yeah, my name is Devin Mackay. I'm a neuro-ophthalmologist at Indiana University. I did my residency at what was used to be known as the Partners Healthcare Program in Boston, and I did a fellowship in neuro-ophthalmology in Atlanta. And I've been in practice now for about ten years.

Dr Monteith: Oh, wow. Okay. Tell us a little bit about your goals when you were writing the chapter.

Dr Mackay: So, my goal with the approach to double vision was really to demystify double vision. I think double vision is something that as trainees, and even as faculty members and practicing neurologists, we really get intimidated by, I think. And it really helps to have a way to approach it that demystifies it and allows us to localize, just like we do with so many other problems in neurology.

Dr Monteith: I love that, demystification. So why don't you tell us what got you interested in neuro-ophthalmology?

Dr Mackay: Yeah, so neuro-ophthalmology I stumbled on during a rotation during residency. We rotated in different subspecialties of neurology and I did neuro-ophthalmology, and I was just amazed by the exam and how intricate it was, the value of neuroanatomy and localization, the ability to take a complicated problem and kind of approach it as a diagnostic specialist and really unravel the layers of it to make it better. To, you know, figure out what the problem is and make it better.

Dr Monteith: Okay, so you had a calling, clearly.

Dr Mackay: I sure did.

Dr Monteith: You talked about latest developments in neuro-ophthalmology as it relates to diplopia. Why don't you share that with our listeners?

Dr Mackay: Yeah. So, you know, double vision is something that's really been around since the beginning of time, essentially. So that part hasn't really changed a lot, but there are some changes that have happened in how we approach double vision. Probably one of the bigger ones has been, we used to teach that with a, you know, patient over the age of fifty with vascular risk factors who had a cranial nerve palsy of cranial nerves 3, 4, or 6, we used to automatically assume that was a microvascular palsy and we just wouldn't do any more testing and we'd just, you know, wait to see how they did. And it turns out we're missing some patients who have significant pathologies, sometimes, with that approach. And so, we've really shifted our teaching with that to emphasize that it's a lot easier to get an MRI, for example, than it ever has been. And it can be important to make sure we're not missing important pathology in patients, even if they have vascular risk factors over the age of fifty and they just have a cranial nerve 3, 4, or 6 palsy. So that's been one change.

Dr Monteith: Interesting. And why don't you tell us a little bit about the essential points that you want to get across in the article?

Dr Mackay: Yeah. So, I think one is to have a systematic approach to double vision. And a lot of that really revolves around localization. And it even begins with the history that we take from the patients. There's lots of interesting things we can ask about double vision from the patient. For example, the most important thing you can ever ask someone with double vision is, does it go away when you cover either eye? And that really helps us figure out the first question for us as neurologists, which is, is it neurologic or non-neurologic? If it's still there when covering one eye, then it is not neurologic and that's usually a problem for an ophthalmologist to sort out. So that's really number one. And then if it is binocular double vision, then we get into details about, is it horizontal or vertical misalignment? Is it- what makes it better and worse? Is there an associated ptosis or other symptoms? And based on all of that, we can really localize the abnormality with the double vision and get into details about further testing if needed, and so forth. I also love that that approach really reduces our need to rely on things like neuroimaging sometimes when we may not need it, or on other tests. So, I think it really helps us be more efficient and really take better care of patients.

Dr Monteith: So definitely that cover/uncover test, top thing there. Your approach- and you mentioned, are you really getting that history, and are there any other kind of key factors when you're approaching diplopia before getting into some of the details?

Dr Mackay: Yeah, that's a good question. I think also having some basics of how to examine the patient, because double vision is such a challenging thing. A lot of us aren't as familiar with the exam toolkit, so to speak, of what you would do with a patient with double vision. And so, I go over in the article a bit about a Maddox rod, which is a handy little tool that I always keep in my pocket of my lab coat. It allows you to assign a red line to one eye and a light to the other eye, and you can see if the eyes line up or not. And you don't need any other special equipment, you just need the light in that Maddox rod. That really helps us understand a lot about the pattern of misalignment, which is really important for evaluating double vision. So, for example, if someone has a right 6th nerve palsy, I'll expect a horizontal misalignment of the eyes that worsens when the patient looks to the right and improves when they look to the left. And especially if it's a partial palsy, it's not always easy to see that just by looking at their eye movements. And having a way to really measure the eye alignment and figure out, is it worse or better in certain directions, is really essential to localization, I think, in a lot of cases.

Dr Monteith: You caught me. I skipped over that Maddox rod part, even though you spent a lot of time talking about Maddox rods. Kind of skipped over it. So, you're saying that I need one.

Dr Mackay: Everyone needs one. I've converted some of our residents here to carry one with them. And yeah, I realize it's a daunting tool at first, but when you have a patient with double vision and their eye movements look normal, I feel like a lot of neurologists are- kind of, their hands seem like they're tied and they’re like, oh, I don't know, I don't know what to do at this point. And if you can get some more details with a simple object like that, it can really change things.

Dr Monteith: So, we’ve got to talk to the AAN store and make sure that they have enough of these, because now there's going to be lots of…

Dr Mackay: We're going to sell out on Amazon today now because of this podcast.

Dr Monteith: Cyber Monday. So, let's talk about the H pattern. And I didn't know it had the- well, yeah, I guess the official name is “H pattern.” In medical school, I mean, that's what I learned. But as a resident and, you know, certainly as an attendee, I see people doing all sorts of things. You're pro-H pattern, but are there other patterns that you also respect?

Dr Mackay: It depends on what you're looking for, I think. The reason I like the H pattern is because you get to look at upgaze and downgaze in two different directions. So, you get to look at upgaze and downgaze when looking to the left, and up- and downgaze when looking to the right. And the reason that matters is because vertical movements of the eyes are actually controlled by different eye muscles depending on whether the eye is adducted toward the nose or abducted away from the nose. And so that's why I love the H pattern, is because it allows you to see that. If you just have them look up and down with just a cross pattern, for example, then you really lose that specificity of looking at both the adduction and abduction aspects. So, it's not wrong to do it another way with, like, the cross, for example, but I just think there are some cases where we'll be missing some information, and sometimes that can actually make a difference.

Dr Monteith: Well, there you have it. Let's talk a little bit about eliciting diplopia during the neurologic exam. What other things should we be looking out for?

Dr Mackay: So, in terms of eliciting diplopia, it really starts with the exam and again, figuring out, are we covering one eye? And figuring out, is this patient still having double vision? It's tricky because sometimes the patients won't even know the answer to that question or they've never done it, they’ve never covered one eye. And so, if that's the case, I really make them do it in the office with me and it's like, okay, well, are we having double vision right now? Well, great, okay, we are, then we're going to figure this out right now. And we cover one eye and say, is it still double? And that way we can really figure out, are we monocular or binocular? That's always step one. And then if we've established that it's binocular diplopia, then that's when we get into the other details that I mentioned before. And then as far as other things to look for, we're always in tune to other things that are going on in terms of symptoms, like ptosis, or if there's bulbar weakness, or some sensory change or motor problem that seems to be associated with it. Obviously, those will give us clues in the localization as well.

Dr Monteith: And what about ocular malalignment?

Dr Mackay: Yeah. So ocular malalignment, really, the cardinal symptom of that is going to be double vision. And so, if a patient has a misalignment of the eyes and they don't have double vision, then usually that means either we're wrong and they don't have double vision, or they do have double vision and they, you know, haven't said it correctly. Or it could be that the vision is poor in one eye. Sometimes that can happen. Or, some patients were actually born with an eye misalignment and their brain has learned in a way to kind of tune out or not allow the proper development of vision in one eye. And so that's also known as amblyopia, also known as the lazy eye, some people call it. But that finding can also make someone not experience double vision. But otherwise, if someone's had normal vision kind of throughout their life, they'll usually be pretty aware of when they first notice double vision. It'll be an obvious event for them in in most cases.

Dr Monteith: And then the Cogan lid twitch?

Dr Mackay: Oh yes, the Cogan lid twitch. So, the Cogan lid twitch is a feature of myasthenia gravis. The way you elicit it is, you have the patient look down. I'm not sure there's a standardization for how long; you want to have it long enough that you're resting the levator muscle, which is the muscle that pulls the upper lid open. And so, you rest that by having them look down for… I usually do about ten or fifteen seconds. And then I have them look up to looking straight forward. And you want to pay careful attention to their lid position as their eye settles in that straight-forward position. What will happen with a Cogan's lid twitch is, the lid will overshoot, and then it'll come back down and settle into its, kind of, proper position. And what we think is happening there is, it's almost like a little mini “rest test” in a way, where you're resting that muscle just long enough to allow some of the neurotransmission to recover. You get a normal contraction of the muscle, but it fades very quickly and comes back down. And that's experienced as a twitch.

Dr Monteith: So, the patient can feel it. And it's something you can see?

Dr Mackay: Yeah, the patient may not feel it as much. It's usually it's going to be something that the clinician can see if they're looking for it. And I would say that's one of the physical exam findings that can be a hallmark of myasthenia gravis, but certainly not the only one. Some others that we often look for are fatigable ptosis with sustained upgaze. You have the patient look up for a prolonged time and you'll see the lid droop down. So that can be one. Ice pack test is very popular nowadays, and it has pretty good sensitivity and specificity for myasthenia. So, you keep an ice pack over the closed eyes for two minutes and you compare the lid position before and after the ice pack test. And in the vast majority of myasthenia patients, if they have ptosis, the ptosis will have resolved, or at least significantly improved, in those patients. And yet one more sign is, if you find the patient's eye with ptosis and you lift open the eye manually, you'll often see that the other eyelid and the other eye will lower down. So, I'm not sure there's a name for that, but that can be a helpful sign as well.

Dr Monteith: Since you're going through some of these, kind of, key features of different neurologic disease, why don't you tell us about a few others?

Dr Mackay: Yeah, so another I mentioned in the in the article is measurement of levator function, which is really a test of eyelid strength. And so, that can be helpful if we have- someone has ptosis, or we're not sure if they have ptosis and we're trying to evaluate that to see if it's linked to the double vision, because that really changes the differential if ptosis is part of the clinical situation. So, the way that's measured is you have a patient look down as far as they can. And you get out a little ruler---I usually use a millimeter ruler---and I set the zero of the ruler at the upper lid margin when they're looking down. So, I hold the ruler there, and then I ask the patient to look up as far as they can without moving their head. Where the lid position stops of the upper lid is the new point on the ruler. And so, you measure that and see how much that is. And so, a normal patient may have a value somewhere between, I don't know, twelve or thirteen millimeters up to seventeen or eighteen millimeters, probably, in most cases. Especially if there is an asymmetric lid position, if you find that the levator function is symmetric, then it tells you that the muscle is working fine and that the ptosis is not from the muscle. So then the ptosis may be from dehiscence of the lid margin from the muscle. And so, that's a really common cause of ptosis, and that's often age-related or trauma-related. And we can dismiss that as being part of the symptom constellation of double vision. So, it can be really helpful to clarify, is this a muscle problem, which you'd expect with myasthenia or a third nerve palsy, or is this a mechanical problem with the lid, which is non-neurologic and really should be dismissed? So that can be a really helpful exam tool.

Dr Monteith: So, you're just now getting into a little localization. So why don't we kind of start from the most proximal pistol with localization. Give us a little bit of tips. I know they just got to read your article, but give us a few tips.

Dr Mackay: So, in terms of most proximal causes, there are supranuclear causes of ocular misalignment. For example, a skew deviation would qualify as that. Anything that's happening from some deficient input before you get to the cranial nerve nuclei, that we would consider supranuclear. So, we also see that with things like progressive supranuclear policy and certain other conditions. And then there can be lesions of the cranial nerve nuclei themselves. So, cranial nerves 3, 4, and 6 all have nuclei, and if they're lesioned they will cause double vision in specific patterns. And then there's also another subgroup, which is known as intranuclear problems with eye alignment. And so, the most common of that is going to be intranuclear ophthalmoplegia. And so that's very common in patients with demyelinating disorders, or it can also happen with strokes and tumors and other causes.

And then there's infranuclear problems, which are from the cranial nerve nuclei out, and so those would be the cranial nerves themselves. So that's where your microvascular palsies, any tumor pressing on the nerve in those locations can cause palsies like that, any inflammatory disorder along that course. Then as we get more distal, we get into the orbit, we have the neuromuscular junction---so, the connection between the nerve and the muscle. And of course, that's our myasthenia gravis. And there are rare causes, things like botulinum and tick borne illnesses and certain other things that are more rare. And then, of course, we get to the muscle itself, and there can be different muscular dystrophies, different things like myositis or inflammatory disorders of the orbit or even physical trauma. So, if a patient, you know, had a trauma in trapping an extraocular muscle, that can be a localization. So really, anywhere along that pathway you can have double vision. So, I love to approach it from that perspective to help narrow down the diagnostic possibilities.

Dr Monteith: Okay, just like everything?

Dr Mackay: Just like all of the rest of the neurology. See, it's not that scary.

Dr Monteith: You know, and so, yeah. And then you do a lot more than, you know, a few cranial nerves, right?

Dr Mackay: Right. That's right. There's a lot more to double vision than that. I think as neurologists, we get lost if it's not a cranial nerve palsy, we're like, oh, I don't know what this is. And if it's not myasthenia, not a cranial nerve palsy. But it's worth also considering that there are ophthalmologic causes of someone having double vision that we often don't consider. So maybe someone who was born with strabismus, or maybe they have a little bit of a tendency toward an eye misalignment that their brain compensates, for and then it decompensates someday and that now they have a little bit of double vision intermittently, so that those can be causes to consider as well.

Dr Monteith: Yeah, well, we'll just have to, you know, request those records from forty years ago. No problem.

Dr Mackay: That's right.

Dr Monteith: Why don't you also give us a little bit of tip when we're on the wards and we want to teach either a medical student or a resident, or if it's a resident listening, may want to teach a junior resident and seem like a star when approaching a patient with diplopia. Give us some teaching pearls.

Dr Mackay: Yeah. So, I would love people teaching more about this at the bedside. I'd say probably the first thing to do would be to equip yourself by recognizing what some of the pertinent questions are to ask someone with double vision. Those things would include, is the double vision worse when looking in a certain direction? Does the double vision go away or not when you cover one eye? What happens when you tilt your head one direction or the other? Is it intermittent or constant? What makes it better? What makes it worse? Those kinds of things can really help us narrow down the possibilities. And then the other thing would be to equip yourself with some tools for examining. And it doesn't have to be physical tools. These can actually be things like, you mentioned the cross-cover test or cover/uncover test. That's described in the article. And I think knowing how to do that properly, knowing how to examine the eye movements properly and how to check for subtle things like a subtle intranuclear ophthalmoplegia, which is also mentioned in the article, being familiar with those things can be a really useful exercise in allowing you to teach others later on.

Dr Monteith: Cool. Why don't you tell us about some of the things you're most excited about in the field?

Dr Mackay: One of the things about our subspecialty for so long is we really haven't had big data with, you know, big trials and all these things that all the stroke people have. And that's starting to change slowly. There's been, for example, the idiopathic intracranial hypertension treatment trial that was published back in, I think it was 2014. You know, of course we had the optic neuritis treatment trial, back a few decades ago now. Some of the exciting ones coming up, there's going to be a randomized controlled trial looking at different treatments for idiopathic intracranial hypertension that are surgically based. So, for example, comparing venous sinus stenting with optic nerve sheath fenestration. And so, figuring out, is there a best practice for surgical intervention for patients with IIH? So, we're starting to have more trials like that now than I think we've had in the past. And so, it's exciting to get to have an evidence base for some of the things that we recommend and do.

Dr Monteith: And what about some of the treatment for diplopia? Like prisms, and where are we with some of that?

Dr Mackay: Yeah, great. So, it's a pretty simple concept, but still kind of difficult in practice. I kind of say there are four different ways to treat double vision: you can ignore it, you can patch or cover one eye, you can treat with prisms, and you can treat with eye muscle surgery. And so, those are the main ways other than, of course, treating the underlying disorder if there's a disorder causing double vision. So those are the main ways to treat. In terms of knowing if someone's going to be a candidate for prism therapy, we also have to remember that prisms are really going to be most helpful for when someone's looking straight forward. So, we need to make sure that their double vision is happening when they look straight forward. So, for example, if they're only having double vision looking to the left or to the right, that patient may not benefit from prisms as much as someone who is having double vision when they look straight forward. So that's one thing I look for. And then strabismus surgery is something to be considered if someone is not tolerating prisms and they're not helping and their eye alignment is stable. So, if you think about it, if someone's eye alignment is changing a lot, you're probably not going to want to do surgery for that patient because it's going to keep changing after surgery. And so, if someone's eye alignment is stable for six months or more and they're not getting the benefit they'd like from prisms, then maybe referral to a strabismus surgeon might be something to consider.

Dr Monteith: Great. And then, I guess another question is just popping up in my head selfishly. What are your thoughts about patients that get referrals for exercises? Say they have, like, a convergence efficiency or something causing diplopia, maybe after a concussion. Maybe there's not a lot of evidence, but what is your take on exercising?

Dr Mackay: Yeah, excellent question. So, there actually is evidence for exercises for convergence insufficiency. So, we know that those do work. Now where exercises are probably not as helpful, or at least not- there isn't an evidence base for them, is really with just about every other kind of eye misalignment in adults. We hear a lot about eye movement therapies for concussion and barely any other acquired misalignment of the eyes as well. And really, the evidence really hasn't shown us that that's helpful; again, with the exception being convergence insufficiency. So, we know that an office-based vision therapy type program for convergence insufficiency does work, but of course it's kind of inconvenient. It can cost money that may or may not be covered by insurance. And so, there are difficulties even with doing that. And so, I often recommend that patients with convergence insufficiency at least try something called pencil push-ups, where they take a pencil at arm's length and they bring it in and exercise that convergence ability. You know, that's a cheap, easy way to try to treat that initially. So yeah, there can be some limited utility for eye muscle exercises in certain conditions.

Dr Monteith: My one example. I was- it was fuzzy, but in a different way. So, what do you do for fun? I mean, it sounds like you like to see a lot of eyeballs?

Dr Mackay: I do. I like to see a lot of eyeballs.

Dr Monteith: When you're not doing these things, what do you do for fun?

Dr Mackay: So, people ask me what my hobbies are, and I laugh because my hobby is actually raising children.

Dr Monteith: Oh, okay!

Dr Mackay: So, my wife and I have eight kids-

Dr Monteith: Oh, wow!

Dr Mackay: Ages three to thirteen. So, kind of doesn't allow me to have other things right now. I'm sure I'll have more hobbies later on, but no, I really love my kids. And I- they give me plenty to do. There's no shortage of- in fact, they were really, they were really excited about this podcast today. They're so excited that Dad gets to be on a podcast, and so I'm going to have to show this to them later. They're going to be thrilled about it.

Dr Monteith: Excellent. Well, thank you so much for being on the podcast.

Dr Mackay: Thank you. It's been my pleasure.

Dr Monteith: Again, today I've been interviewing Dr Devin Mackay about his article on approach to diplopia, which appears in the most recent issue of Continuum on neuro-ophthalmology. Be sure to check out Continuum Audio episodes from this and other issues. And thank you to our listeners for joining today.

Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.