Lecture: Fourth Nerve Palsy: Tips & Tricks to Understand and Treat

Fourth nerve palsy whether in kids or in adults seems to be a difficult topic to understand and interprete whether for ophthalmology residents or the general ophthalmologist. Here is a very simple and down-to-earth way to understand the signs and decide management modalities.

Lecturer: Dr. Alan Mulvihill, Princess Alexandria hospital, Edinburgh, Scotland
Panelist: Adedayo Adio FWACS, Consultant Pediatric Ophthalmologist
University of Port Harcourt teaching hospital, Nigeria.
Chairperson, Nigerian Pediatric Ophthalmology and Strabismus Society (NIPOSS)

Transcript

[Adedayo] Hello, everyone. Welcome to the second in a series of webinars in a session with Cybersight. Today we’ll be talking with Alan Mulvihill who is talking about fourth nerve. The evaluation and tips that we need to understand and every kind of trick that we can employ to be able to help us make a good diagnosis. But before then, I will just say a little bit about what NIPOSS is all about. The society of all pediatric ophthalmologists in Nigeria who are committed to ensuring the overall eye health of the Nigerian child. And we’ve been together like this for a decade now. And we have noticed that some of us live in a very diverse society, almost 200 million population, we live in different parts of the country. To come together is a challenge. But we would like to have continuing medical education and this came about with a collaboration with Cybersight. Also, Nigeria, because of NIPOSS, training from different parts of the world, we have people from India, Zambia and very far away from here. So interesting about Nigeria is also important.
We have a population of about 186 million with 90 million under the age of 18 years. Our capital is Abuja. We just finished celebrating Children’s Day in Nigeria this last Monday. And all of our country, all of our pediatric ophthalmologists were together in different, with their children, celebrating with them, having a great time, and we all had a lovely time together.
We’re just 37 in number. And that is just less than 10% of the entire number of ophthalmologists in the whole country. But we are spread in 21 centers all over the country. You can see in all those dots all around the place. But we have, most of us concentrated in the southern parts with very few in the northern parts of the country. So this collaboration with Cybersight is, like I said, is born out of a need for continuing medical education. And it’s supposed to happen every quarter, we had one earlier in the year and we’re going to have two more before the year runs out.
Today we’ll be discussing fourth nerve, tips and tricks. Why this topic? This topic is perceived to be very difficult to understand. Those of us who relates with residents know that it’s a very difficult topic. They’re always complaining they can’t understand it, they fail to remember, it’s very labile in the memory. So we’ve brought in a very distinguished guest. He’s a consultant pediatric ophthalmologist who works in Princess Alexandra Eye Pavilion in Edinburgh. He’s been there since 2002. He had his clinical fellowship training in pediatrics at Moorfields Eye Hospital and Hospital for Sick Children in Toronto. And his areas of interest is in general pediatric ophthalmology, pediatric and adult strabismus, and also he screens children for ROP.
I was with him in 2016 and had a very stimulating time together. And this is our distinguished guest, Dr. Alan Mulvihill, he’s going to be talking to us about fourth nerve palsy. Make sure to write down all your questions, all your queries, every area that is difficult for you to understand and he will speak to us in a way that is in an interactive manner. And he’ll take all questions. Thank you very much for coming. All right, over to you, Alan.
[Alan] Okay, thank you Dr. Adio. Hello, everybody. I’m going to approach this, not necessarily as a completely didactic lecture, but a sort of series of learning points. And try to have an evolving and teach you an approach of history, examination, and management of patients with fourth cranial nerve palsy.
I think it’s worth starting with anatomy. Fourth nerve, its nucleus is in the midbrain. The nerve leaves the nucleus, passes through the substance of the midbrain, decussates in the posterior medullary velum, and then wraps around the midbrain to the front of the midbrain, passes through the cavernous sinus in the lateral wall of the cavernous sinus, and into the orbit. So it has the longest intracranial course of any nerve and it decussates within the brain, which is highly unusual. But it’s that long course that makes it vulnerable to various things, including traumatic injury.
As you know, the fourth nerve only supplies one structure, the superior oblique muscle, which is quite an unusual muscle. It runs along the superior nasal wall of the orbit, it reflects through the trochlea to become a tendon that’s wrapped around the globe. And it has actions that are primarily first intorsion, or rotating the globe, on its anteroposterior axis. Has some abduction effect and it has some depression effect. And all these are important.
There’s various causes of fourth nerve palsy. Probably the commonest one, certainly if you’re practicing pediatric ophthalmology, is some form of congenital fourth nerve palsy. That term has been a little bit controversial in recent years because there’s some evidence that it might be a purely myogenic, or muscle development problem. But there’s also some evidence that it might be a developmental problem of the fourth nerve nucleus or the nerve itself. So whether it’s truly myogenic or neurogenic, is a little uncertain. But it’s certainly a common childhood problem. The vast majority of childhood fourth nerve palsy sit into this category.
I’ll talk in a little while about traumatic fourth nerve palsy that tends to occur in closed head injury. But that can occur in children, it’s more likely in adults. And middle age to older adults, some form of microvascular fourth nerve palsy, basically arterial disease is the most common cause. And then there’s some rare outliers to just tumors and aneurysms and treatment for tumors and other problems.
The so-called congenital fourth nerve palsy. It’s presumably present from birth but often only becomes noticeable later on. Sometimes in the first six or 12 months of life, but often later. I saw a child yesterday who was only picked up at our national preschool vision screening program. So at about about age four, four and a half, where an orthoptist examined this child and noticed a head tilt and a small vertical squint. And the parents had never been aware of it. The child’s not having a problem, the parents are happy. So we’re just electing to observe. But it’s a very big spectrum from big head tilt and all sorts of problems with adopting a torticollis, or head tilt, to keep the eyes aligned to almost negligible problems.
The typical congenital fourth nerve palsy. And I’m going to use that term, I understand that some people disagree with the term. But I think it’s helpful because we know what we’re talking about. One of the commonest, probably the commonest feature is a compensatory head posture or tilt to the opposite side, or away from the side of the palsy. Children may be noticed to close one eye when they’re reading or when they’re tired. Double vision is uncommon, it’s very uncommon for children to report double vision with this condition. But they may, when they’re old enough, report that their vision is a bit blurred or their eyes ache at times. So they might have eye strain symptoms. If they’re old enough to be able to measure a vertical fusional amplitude with a prism bar, they’ll have a large fusional amplitude vertically. Most of us who don’t have any sort of congenital fourth nerve palsy or other vertical ocular motor misalignment, might have a tolerance for overcoming just one or two prism diopters worth of vertical prism. People who have a long-standing fourth nerve palsy, where they’re controlling it with binocular vision, could have 10, 12, or more prism diopters of vertical fusion range. Which tells you they’ve been dealing with it for quite a long time.
Often when you examine people, they can have excyclotorsion of the eye. When you look in the back of the eye, I’ll have a slide on that in a minute. Rarely, if ever, are people with a congenital fourth nerve palsy aware of torsion. They don’t appreciate tilting vision.
In my experience, these have a habit of gradually getting worse over the years. Most, but not all, get to the point where it becomes intolerable and the head tilting, or sometimes prisming glasses isn’t enough and you eventually have to consider some form of squint surgery. It’s not inevitable, but I think a very large proportion just gradually worsen. It’s like an elastic band that stretches and stretches and just reaches a point where it just can’t give anymore.
And finally, facial asymmetry is not that uncommon. Because of the tilting, over time, it seems that the face, the growth of the facial bones changes. I’m sure you’re all aware of that. It can be quite subtle. But it’s perhaps an argument for intervening surgically sooner rather than later. But it’s always a bit of a difficult sell to parents, because if their child is generally happy and they haven’t noticed a problem until somebody points it out, I always try and let the parents come to their own decision on that and try and nudge them. But I’ll never tell them that their child needs a treatment.
Next I want to talk a little bit about traumatic fourth nerve palsies. It tends to occur in young to middle aged adults. Sometimes can occur in sports, road traffic accidents, all sorts of trauma, falling off walls. Young men who work as builders, working construction, they fall, whatever. Working in agriculture and industry. Young men tend to be a little bit more reckless and a little less safety conscious than the more mature of us. Well, I use that word advisedly, but a little older and a little more aware of our mortality. But it’s generally a condition of young to middle aged adults. There are exceptions to that and occasionally you see it in kids.
So typically it occurs with a closed-head injury. People have a whiplash injury or a concussion playing sport, or they fall off a wall, or off a bicycle. If they’re unconscious, obviously, they’re not going to notice double vision until they regain consciousness. Whether that’s days or weeks later. Even if they have only a brief concussion or loss of consciousness, often the symptoms aren’t there on day one. It might be a day or two before they become symptomatically aware. So just because they only become symptomatic a day or two later, it doesn’t mean they’re inventing the symptoms. And that seems to be quite common..
Often they may report vertical double vision in primary, they might or might not be aware of some tilt or torsion in primary gaze. But torsion trends to be more symptomatic in down gaze. And torsion is a very big factor in traumatic fourth nerve palsy and it’s quite often the most troublesome problem for the patient. And the one that it’s hardest for us to manage.
But the good news is, it’s a very high rate of recovery. Depending which scientific paper you read, or your own personal experience, it varies from 50, to 75, 80% or even higher. It’s definitely worth waiting as long as possible. I would wait an absolute minimum of six months, and preferably up to a year before intervening surgically. And try and manage the patient with prisms, and usually press-on prisms on glasses. Because it tends to be a moving target. So I would rarely, if ever, go for ground-in prisms, unless the patient is particularly unhappy about press-on prisms and is happy to spend money every time they need to change a prism, but that’s pretty rare.
And the final thing about traumatic fourth nerve palsy is they’re often bilateral. They may be asymmetric, and you may not be able to see the fourth nerve palsy on the other side. But you always have to have in the back of your mind the possibility that it might be bilateral. Especially if there’s higher degrees of excyclotorsion. If there’s more than eight or ten degrees of excyclotorsion, I think you need to be very suspicious that this might be bilateral.
Microvascular fourth nerve palsy is something that occurs in older people, usually above age 60. It can be below that, but if it’s below age 60 I’d be a little bit suspicious for other causes. It’s typically a sudden onset, they wake up with it, or it comes on over a few hours. There’s usually no associated headache, nausea, vomiting, it’s usually not part of a wider stroke situation. It’s just an isolated event. It’s usually unilateral, often the patients have hypertension, diabetes, the usual cardiovascular risk factors. They might be smokers.
And what I do with these patients, I take careful history and I examine them, including examination of the fundus, a quick cranial nerve examination. Which, if you’re experienced, you can do a quick cranial nerve examination in under a minute. Even in a busy clinic, you can do a quick cranial nerve examination, quick confrontation visual fields. If the history and the examination feel right, I don’t investigate further. Certainly for the first few months.
If it gets to about three months out, and there’s no sign of improvement, I tend to, in the past I didn’t, but now I’m more inclined to do neuroimaging. The one thing that can sometimes minic a microvascular is patients with a condition like meningiomas around the cavernous sinus on the greater wing of sphenoid. More likely they’ll present with a third or six, but occasional a fourth nerve palsy is not completely unknown. And they can have a funny course. They can come on quite quickly, they can improve, and then worsen again.
Usually there’s no intervention, but people don’t like that a diagnosis like that has been missed. But in the normal situation with a microvascular fourth, I would just observe and manage with prisms if possible for the first three months or so. If they’re starting to improve, or they’ve gotten better by three month, fantastic. If they’re not improving and certainly if there’s any worsening, if the measurements are increasing, then I would do neuroimaging. And the test I would do would be an MRI scan of the brain and orbits. So I’ve mentioned, otherwise, neuro-ophthalmic examination.
I’ll add there’s some miscellaneous ones. Tumors, or its treatment, pretty rare causes of fourth nerve palsy. Not impossible, but very rare. But if the situation is changing, if it’s worsening, especially if it’s worsening over a few months, rather than over a few years. Congenital fourth nerve palsies can gradually worsen, but it tends to be very slow over many years. If it’s worsening over a period of a few months, I’d be worried. After vasculitis conditions, such as Zoster. I’ve seen quite a number of cranial nerve palsies, they tend to get better. Usually all resolve. And then myasthenia, a great mimic condition, it can mimic just about any muscular ocular motility disorder. It’s always there in the back of our minds. It’s the commonest blood test that I order. I don’t tend to order full blood counts and renal function tests very much because I’m not seeing patients with many systemic diseases. But I ask for acetylcholine receptor antibody test very frequently.
Regarding the assessment of fourth nerve palsy, history’s always important. We were taught this in medical school and it applies even in a very specialist clinic. You make the most of your diagnosis on the basis of history. And while you’re taking the history, you’re also observing the child or adult. Is there a compensatory head posture, is there monocular eye closure, is there facial asymmetry? All sorts of other things. Do they walk into the room normally? Are they ataxic? Do they have poor vision? All these things are all really important, we all do them probably unselfconsciously, without realizing it, it becomes part of our normal routine. And a full ophthalmic examination. Even if they’ve been referred by another ophthalmologist, but it’s someone who’s not a pediatric ophthalmologist, or strabismus specialist, or if the previous doctor who saw them was maybe a resident, don’t accept the diagnosis at face value. Always take some history yourself. As in all patients, you need to do measured vision, you do fundoscopy, motility, and prism cover testing. I’m a very big believer in doing the examination myself.
We have great orthoptists in our department, but I like to do my own motility examination and measure the prism cover test. And measure it in the different positions of gaze. Again, it’s like the cranial nerve examination, if you do it regularly, you become quick at it. When Dr. Adio was in our hospital, I think she probably saw me using the prism bars a lot. It’s like anything, the more you do it the better you get. And you become confident about your examination.
Here’s a typical fourth nerve palsy case, could be a child, could be an adult. In this situation, I’ve put a history. It’s a 25-year-old who reports gradually worsening of eye strain symptoms over several years. And has become aware that they’re tilting their head to the right. And if you look at the motility exam, we could record it in different ways, I tend to record it this way. Can you see the pointer there? Dr. Adio? Is it moving on the screen?
A left hypertropia, on left gaze it’s negligible, just a flick of hyperphoria, but it increases on right gaze and on left tilt. So I think most of us would say that’s a pretty typical fourth nerve picture. It’s also present when you measure for near, about a third of a meter on distance. The left inferior oblique muscle is overacting. The superior oblique is mildly underacting. When you look at the opposite eye and the right eye, there’s an apparent under-action of the opposite superior rectus. Isolated superior rectus under-action is really, really rare. It’s usually the opposite fourth nerve. But sometimes it can get diagnosed as a sort of under-action.
But what we’re seeing here, we’re seeing this asymmetry goes from a foot, nothing in left gaze to something moderation in primary position, to big on contralateral gaze and on ipsilateral tilt. Let’s come back to that in a moment.
On examination, you notice the patient has a degree of facial asymmetry. And when you look at the back of the eyes, there’s fundus excyclotorsion, but the patient reports no torsion and they’ve no measurable torsion. They just have vertical. When you disassociate the eyes, on cover and uncover test, they briefly have vertical double vision but are able to bring the eyes back together using their motor fusion.
And finally, the patient has a big vertical motor fusion range of about 10 to 12 prism diopters. So this all feels like a long-standing fourth nerve palsy. It’s very reassuring. The features are all sort of what you might call typical. Facial asymmetry, fundus excyclotorsion, and a large vertical motor fusion range.
I have to confess, I don’t look for fundus excyclotorsion that often. But when I look for it, I’m also expecting to find it. Normally when we look at the back of the eye, as you know the fovea should be just very slightly below the level of the optic disc. Both these eyes, it looks like the fundus is excyclotorted a bit, especially the left fundus. But in somebody who has a congenital fourth nerve, they might be completely asymptomatic with regard to torsion.
Again, the critical examination points, so gradual onset, large vertical fusion range, that points to a long-standing problem. And there’s the typical oblique muscle pattern which is nothing-something-worse. So when you have an oblique muscle problem to go from nothing here, something worse. The case I’ve just shown also follows Park’s three-step test, which I’ll come on to in a moment, and that’s a very helpful test. Because it pulls together various aspects of the eye, of the motility examination. Which as Dr. Adio mentioned, often sort of bamboozles trainees somewhat because there’s different things happening in different directions of gaze. You have to think in three dimensions. And in the typical case I’ve just described, cranial nerve examination was normal, confrontation visual fields are normal.
So I mentioned again, about oblique muscle dysfunction. A very helpful phrase I was taught when I was in Toronto by Dr. Steve Craft, who’s the strabismus expert there was, if it’s an oblique problem it goes from nothing-something-worse. So in the case I demonstrated, so on left gaze there’s nothing, primary gaze there’s something, on right gaze it’s worse. So just bear that in mind. It’s a very useful framework to have in the back of your mind when you’re assessing somebody with a motility problem.
Park’s three-step test, you’ve probably heard of that, it’s a very useful thing. It’s particularly useful for residents, but it’s still helpful to think of it ourselves because it gives you a basis for moving forward. So step one is a hyper-deviation. So the case I discussed, the left sided hypertropia, or intermittent hyperopia. So I’ve recorded it there as the T for tropia in brackets. So it’s an intermittent. On contralateral gaze, the deviation increases significantly. And that’s step two. And then the third step is on ipsilateral head tilt, it increases. And it’s important to measure in tilt to both sides. And if it’s asymmetric, it’s very helpful. So it increases on the ipsilateral tilt.
The Park’s three-step test, described by Marshal Park, who’s one of the founding gurus of pediatric ophthalmology. He was a very distinguished ophthalmologist, and I think he was in Washington Children’s Hospital. I had the honor of meeting him in his latter years, he’s now sadly deceased. But he was one of the great inspiring figures and a great clinician. He examined patients carefully and he was an honest clinician. He was able to say which tests work, which operations worked, which ones didn’t. An open, inquiring mind, which is exactly what you need.
The three-step test, very helpful. Once again, an ipsilateral hyper-deviation, step one. Increased on contralateral gaze, step two. And an ipsilateral head tilt, step three. It’s present in most, but not all fourth nerve palsies. If it doesn’t follow the three-step test, especially the head tilt component, I think you need to be a little bit suspicious. You need to step back and think, “Is this really a fourth nerve palsy or is this something else?” It’s not always present, so just because it’s not present, doesn’t mean it isn’t a fourth nerve palsy, but it does mean that you need to think again.
And finally, measuring torsion. Torsion is probably the most difficult thing I find to measure. I’m very happy to do prism cover testing and different positions of gaze. But there’s various methods for measuring torsion. The Maddox wing is probably the simplest instrument, but I’ve never been terribly impressed by it for measuring torsion. I’ve always considered it to be something like a random number generator. You never get the same answer twice.
The Double Maddox rod test is probably the best test, if you don’t have an orthoptist who can measure torsion for you on a synoptophore. I’m very lucky to work with a great bunch of orthoptists. And if I’m suspicious of torsion, or I know there’s torsion, I’ll ask them to measure it with a synoptophore in the various positions of gaze. But especially primary position and down gaze.
In some orthoptic departments it tends to gather dust, but it should be an instrument that’s in regular use. It’s old fashioned, it looks like it was made in the 1950s, but it’s still a really important, invaluable piece of equipment. Hess chart or Lees screen, in our department we don’t tend to do them terribly much. Partly because they’re time-consuming for the orthopists. I think, personally, I find examining the patient myself and doing the prism cover testing and different directions of gaze, I find that the most helpful for me. For people who are non-motility specialists, they like the Hess chart because… I always think of it is most helpful for people who can’t do cover testing themselves.
I’ve worked with a big department of maxillofacial surgeons who deal with a lot of orbital fractures and they really like having Hess charts before and after orbital fracture repairs. I think that’s fair enough. Because they like to be able to show whether they’re making things worse or better. But from my point of view, I don’t need it, I make my own decisions on the history and examination. And the Hess chart I show there, it’s showing a typical fourth nerve palsy on the left side with superior oblique under-action and inferior oblique overaction.
This next one shows a right fourth nerve palsy, where again, superior oblique under-action, inferior oblique overaction, but this part of it, the Hess chart on the right side, the bottom part shows some torsion. That’s what torsion looks like. I had to get these from Google images because I don’t have any myself because we rarely do them in our department.
Most of the time, I’m happy to make the diagnosis on history and examination. Occasionally I’ll do some other test. And the commonest test I do is a blood test for myasthenia. If the history seems like it might be changing or if it’s variable, disassociated ptosis, I think it’s worth checking for acetylcholine receptor antibodies. Sometimes if you get an equivocal result, which you can because you can have antibody negative myasthenia, probably the best test is a trial of pyridostigmine or mestinon. Probably need to do it for several weeks and you gradually build up the dose.
Occasionally I will do an MRI scan, especially if it’s a atypical one, that shows where the patient is quite clear that there’s no history of head injury, but they’ve had progressive symptoms. Over the years I’ve diagnosed one or two fourth nerve schwannomas and other things. It’s pretty rare, but they can occur. So if the history or examination is atypical, I do sometimes order an MRI scan. But I think a CT scan in this situation is not the right test. It has to be an MRI scan. And crucially, for me, it’s not just the scan but the radiology doctor who reports the scan. Again, ideally it’s a neuroradiologist as opposed to a general radiologist.
So, treatment planning. We’re back to this case that is sort of typical fourth nerve palsy that we discussed a few minutes ago. So it’s got the classical nothing-something-worse pattern, it’s a left hypertropia, and there’s various approaches. I think for most of us, the most common surgical approach. I’m presuming here that conservative measures aren’t working. If it’s an adult that either prisms are intolerable, or they’re not satisfactory, or they’re just unexceptable, they don’t like wearing prisms and glasses, or they’re may be an myope and they want to wear contact lenses and they can’t put prisms in their contact lenses. But I haven’t talked too much about the conservative measures today. Perhaps I should have put a slide or two in about that. Taking a step back, I think it’s always worth, we always try and manage these things conservatively if possible. Because I’ve had my fingers burnt a few times after surgery with people who aren’t happy with the outcome, so it makes you a little bit cautious. Surgery is always the last resort. But in fourth nerve palsy, you often are at the last resort quite quickly.
For a typical fourth nerve palsy, inferior oblique weakening is probably the simplest and probably the commonest operation. My personal preference is a myectomy and disinsertion of the inferior oblique. I know that some people like recession of the inferior oblique, but I’ve tried that but I find myectomy and disinsertion works better for me. But I think you’ll find plenty of people who say a recession is better or it’s their preferred option. I don’t think there’s a great amount of evidence one way or the other.
There’s a small subset of strabismus doctors who might do anteriorization of the inferior oblique to alongside the lateral border of the inferior rectus. I don’t tend to do this for fourth nerve palsy, but I do use that operation for dissociated vertical deviation. For which, I think, it is by far and away the best operation.
Inferior oblique weakening. When I do an inferior oblique weakening, I do an inferotemporal fornix incision between the inferior rectus and lateral rectus. I put in a retractor, personally I prefer a Fliesen retractor, to pull the tissues back. And I try and visualize the inferior obliques before hooking it. So I don’t put a squint hook in blindly, I identify where the muscle is. Once I’ve got the muscle hooked, I then, with a second hook, I put a hook underneath the lateral rectus and then under the inferior rectus, to make sure I’ve got the correct muscle. Because what you don’t want to do is cut off the wrong muscle, because that would be a disaster.
Once you’re sure you’ve got the correct muscle, you also need to double check that you’re not near the… Usually the lateral rectus will be over here and the inferior rectus here. I tend to try and hook it closer to the lateral rectus end. Because if you lift the muscle forward, and look down there. You usually see a vortex vein, and you don’t want to damage the vortex vein and get lots of bleeding.
So I stretch the inferior oblique as gently as possible between two squint hooks, I put two artery clamps on, and I remove the piece of muscle in between. I try and remove at least four or five millimeters of muscle, maybe more. And I cauterize the ends and then I let the proximal portion just rebound back into the orbit. Before I remove the clamp on the distal end, the bit that’s attached to the sclera, I use as a handle to pull the eye upwards. And with a retractor, you get a really good view down into the muscle cone and see are there any residual fibers of inferior oblique. Sometimes it’s quite easy to not hook all of the muscle and to leave fibers behind. Because you can inadvertently split the muscle or sometimes it can be an anatomically split muscle with a split insertion like that. So it’s possible to miss fibers of the inferior oblique. So you have to specifically think of that and look for it.
But before you remove the clamp attached to the distal end that’s attached to the sclera, it’s a really good handle for just gently bringing the globe up, put a retractor in and look down the hole, because you don’t want to leave any attached fibers. I then tend to do a two-layer closure, firstly of the tenons and then the conjunctiva with 6-0 Vicryl.
Now, just a couple of points. One is I always say to residents, it’s a bit like being in court where you’re told the truth, the whole truth, and nothing but the truth. But it’s the muscle, the whole muscle, and nothing but the muscle. It’s about the muscle, so the correct muscle. Make sure you cut the inferior oblique and not a rectus muscle. The whole muscle, so you get all of the muscle, and make sure you’ve got all of it, and nothing but the muscle. So don’t get involved in orbital fat and things like that where you can cause an adherence syndrome.
Also, don’t pull too hard on the inferior oblique because you can pull on the neurovascular bundle that supplies the inferior oblique and you can damage the nerve supply. And not just to that muscle, but the inferior division of the third nerve which also supplies the pupil, and you can end up with a permanently enlarged pupil or mydriasis. So you have to be careful not to put too much traction on the inferior oblique.
What I find after surgery, is it tends to be pretty good in the primary position, but the patient can still be symptomatic on contralateral gaze. And in virtually all cases, if you wait between three and six months, and sometimes more, it just fixes itself. Because these patients do all have binocular vision and motor fusion. And basically the brain resets and recalibrates all the muscles over a series of months and it virtually always fixes itself. So if you’ve chosen the right operation, even if it’s not right initially, it tends to improve. I always warn patients about this in advance. I always advise them that it’ll improve but you may not get all the improvement initially.
And the other thing I always specifically warn the patient or parents, if it’s a child, about, that even if it looks unilateral sometimes it can be bilateral and you only know that when you operate. And then over three to six months, the deviation goes the opposite way and you’ve unmasked the same problem on the other eye. So it’s about a 5% or one in 20 chance that that will happen. So when I’m consenting patients for surgery, I specifically say that there’s about a one in 20 chance that we might unmask the same thing on the other eye. So if it happens, it happens, nobody’s happy about it, but nobody’s desperately unhappy because they were warned.
Now, I’ve mentioned that inferior oblique weakening is my preferred procedure for fourth nerve palsy and that works for the majority. But you have to be careful, if there’s marked under-action of the superior oblique, then weakening of the inferior oblique alone is not enough. So if we look at these nine positions of gaze picture on this side of the slide. If you look at when the patient is looking down to the right, the left eye’s going down reasonably well. When they’re looking down to the left, the right eye is not going down very well at all. It’s going down very poorly and that’s something you need to be wary about. If you’ve got significant under-action of the superior oblique, like -3/-4 under-action, you’re going to have to do a superior oblique tuck. So an inferior oblique won’t fix that, it needs to be a tuck. And that’s something that people are less enthusiastic about. But there are times when you have to do it.
So it’s an operation I do much less frequently, maybe once or twice a year I do a superior oblique tuck. But it’s one of those things the more you do it, the more confident and happier you become about it. I tend to approach it in the superonasal quadrant. It’s actually quite easy to find the superior oblique tendon there. In the pictures, the series of pictures on the right hand side, which I got from Google images, somebody’s using a tucker, there is an instrument specifically for tucking. But if you don’t have that, what you need is an assistant. You need them to lift the tendon up with a hook, and you put two non-absorbable sutures down at the bottom here, where you lift the muscle up, and do a knuckle, like a redundant loop. And I use a 5-0 Dacron and I tie it into a bow-knot, a temporary knot. And what I think is the right amount of tightening or tucking, and then you have to do a forced duction test before you tie the stitch off.
And what you’re aiming to do is when you try and elevate the eye, the inferior limbus should be able to come up just about to the horizontal midline. It’s very difficult to demonstrate in a picture. But you want to be able to bring the inferior limbus just about to the horizontal midline and not beyond. And if you think you’ve got it about right, then you tie off your previous stitches. But it’s important to do an intraoperative forced duction testing before. You need to check it before tying it off. Difficult to demonstrate here, I don’t have a video of it, but if you’re doing a superior oblique tuck, there are plenty of videos on YouTube and Vimeo if you want to have a look at that.
I want to talk a bit about torsion or excyclotorsion, which is particularly something that occurs after traumatic fourth nerve palsy. Also sometimes with fourth nerve palsies following treatment for brain tumors. I mentioned before, wait at least six and preferably 12 months before operating. Because it often improves and that’s the best treatment of all. And I mentioned also previously, suspect a bilateral palsy, especially at higher degrees of excyclotorsion. If it’s above eight or 10 degrees of excyclotorsion, I think I’d be very suspicious that it might be bilateral.
Surgical options, well, probably the best surgical option if it’s isolated torsion, is the Harada-Ito procedure. Where you find the anterior portion of the superior oblique tendon, you split the superior oblique tendon, you put a stitch into the anterior portion, and advance it down towards the upper border of the lateral rectus.
Here’s a diagram I did previously to help understand that this is looking from above. We’re looking at the left eye. Here is the superior oblique muscle, the trochlea, the superior oblique tendon, which is reflected from the trochlea, passes underneath the superior rectus here. And I approach it from the temporal side, so a suprotemperal incision. You hook the superior rectus, then you pass a second hook between the superior rectus and the superior oblique to break the frenulum between the two. And then you definitely need a good assistant for this. The assistant brings the eye forward using the hook under the superior rectus, and you find the superior oblique tendon and you split it in half. I then suture it with a double armed 6-0 Vicryl suture. You need to split the superior oblique tendon at probably at least six to eight millimeters, you are as far back as you can to separate it from the posterior portion. The posterior portion is mainly depression and abduction. The anterior portion of the superior oblique tendon is the incyclotorsion part of it.
Once you’ve secured it with a 6-0 Vicryl, and you’ve detached the anterior portion of the tendon from the globe, you advance it towards the lateral rectus. Not towards the insertion, but maybe six, seven, eight millimeters behind the insertion of the lateral rectus, and bring it as close to the lateral rectus as you can. Just stretch it as far as it’ll stretch, and you suture it to the sclera. Often the superior oblique looks really small and diaphanous and you wonder how could this possibly fix anything? But when you do it properly, it’s an operation that could work really well. It’s a really effective treatment for torsion. It has negligible effect on any vertical squint. So it only addresses the torsion.
I’ll just go back a slide. The other operation that can sometimes help torsion is if you happen to be operating on an inferior rectus, is to move it nasally by a half to two-thirds of a tendon width. I’ve only had to do that once or twice and it has worked pretty well. But I have to say, my procedure of choice for excyclotorsion is the Harada-Ito procedure. It’s a really great operation and by far and away the best operation to correct excyclotorsion in a fourth nerve palsy.
Next, I’ve got a couple of typical cases. They’re all cases that I’ve dealt with myself. This is basically the case that we discussed before. It’s the typical fourth nerve, where it’s a long-standing symptoms, large vertical fusion range. The example I’ve given is a 25-year-old but it could easily be a five-year-old. Where they have the typical nothing-something-worse going from left gaze to primarily position to right gaze, a vertical squint, and there’s a significant difference in the squint with head tilt, to increasing on ipsilateral gaze, increasing to the side of the palsy. The significant overaction of the inferior oblique, I’ve written a +3 overaction. There’s sort of mild to moderate under-action of the superior oblique, I’ve written -1. In this situation, weakening of the left inferior oblique is the most straightforward operation.
Now, here’s something a little bit different. Let’s say it’s the same patient, it’s a 25-year-old, gradual worsening of eye strain symptoms and increasing head tilt. No symptomatic excyclotorsion. This is a bit different. If you look here, there’s quite a big deviation of primary position, it’s 14 hypertropia, it’s bigger on right gaze. But on left gaze, it’s still a significant vertical deviation. They’re able to control it so it’s an intermittent, but it’s measuring 10 diopters of hypertropia. So is this a fourth nerve palsy? I think if you look at it logically, well, there’s something worse and something even worse. And the head tilt is positive. So when you tilt to the ipsilateral size, it’s very different to when you tilt to the right side.
What this is is a long-standing fourth nerve palsy, where over time the deviation has become so big that it’s also present on ipsilateral gaze and there are fourth nerves that are like this. This is a fourth nerve palsy, it’s just a very big one. On contralateral gaze, it exceeds the size of the biggest prism on the vertical prism bar.
What’s the approach here? As I mentioned, it obeys the three-step test. But the operation we did for the previous case, the inferior oblique weakening, it’ll help this somewhat, it’ll help that. But it’s not going to do anything over here because a bit like an oblique muscle problem, oblique surgery will have no effect here. So you need to do something for this as well. So what you need to do in this situation is firstly weaken the left inferior oblique, but it might be enough. And what I do, and I discuss it with the patient and I would say, “This will improve things here, it will improve things here. But maybe not over here. If you just weaken the inferior oblique it might be enough, but it might not.”
And what I often do, in this situation, is I would weaken the left inferior oblique, but also the right inferior rectus. So I would say that approximately 10 or so prism diopters of the height needs to be corrected by the inferior rectus, because this over here on the left gaze represents a rectus muscle problem and also a rectus muscle solution. You have to be careful not to overcorrect it though, because what these patients don’t tolerate is over-correction. This patient will have been dealing with the left hyperdeviation for many years. If you reverse it to give them a right hypertropia, he’ll be very unhappy.
So if you’re going to do something to the inferior rectus, make sure you under-correct them a little bit. I would do a small recession of the opposite inferior rectus and I might well use an adjustable suture. I say “might well” because it’s hard to be certain. This patient has motor fusion of binocular vision. Personally, I think you can get away without an adjustable suture, I know a lot of surgeons will say you must use an adjustable in this situation. I think if you do a modest amount of weakening of the inferior rectus on the opposite side, you’ll probably get a very good result. If you have to error one way or the other, err on the side of under-correction. 10 diopters of hyperdeviation over here, I would do at most 3 millimeters of recession of the opposite inferior rectus.
Right. Now here’s another case, I’m just going to see if I can move this year. Right. This is a bit different, again. Now, let’s say you’ve been asked to see a patient by a resident or it’s been referred by a colleague who’s not quite sure what to do. Or say, “I’ll do a straightforward horizontal squint, but I don’t like doing verticals. So Dr. Adio, I’m going to send it to you because you’re the expert.” Now, there’s a right hypertropia, maybe a little bit bigger primary gaze and a little bit bigger again on left gaze. But look at the head tilt, there’s no difference. So we do look at the motility, the right eye’s tending to go up a lot, the left eye just seems to have a restriction across the board. So you just need to be a little bit suspicious that there’s something else going on.
Just because it’s been referred to you as a fourth nerve palsy, it’s worth sitting back and scratching your head and having a bit of a think about it. For some people who don’t do motility a lot, general ophthalmologists or trainee eye doctors, sometimes every vertical is a fourth nerve palsy. We all know that it’s not that simple. It is the commonest vertical eye movement problem, but it’s not the only one.
Would you sit back and have a look at the patient, think there’s a bit of fullness on their left upper eyelid. And this is a patient I saw a few months ago and I sort of inquired a bit more. I asked, “Are you generally well?” And she said, “Yeah.” It was a lady in her early 50s, she’s a healthy lady. I asked, “Any sinus problems? You get blocked nose and nasal discharge?” And she said, “Yeah, I’ve had that for years, it’s ongoing.” So I did an MRI scan. And what this lady turned out to have, is she had, this is her frontal sinus, she had a lot of stuff going on there, and she had stuff in her orbit. Turns out she had a frontal sinus mucocele.
Depending on what part of the world you live in, other diagnoses might be more common. If you live in southeast Asia, nasopharyngeal carcinoma is a very common cause of something like this. But that’s a very rare cancer in my part of the world. So for a deviation that’s relatively even across the piece. That’s more like a rectus muscle problem or a mechanical problem. So always be suspicious. If it doesn’t follow the three-step pattern, ask some more questions. Don’t be afraid to do a scan or investigation. Just because it’s been referred to you as a fourth nerve palsy, doesn’t mean it’s a fourth nerve palsy. Right.
This is a different patient. This patient came to me with a diagnosis. He’d had a brain tumor a few years ago in his posterior fossa. He’d had surgery and he’d been left with a double vision problem. He’d had a right fourth nerve with some vertical double vision and some excyclotorsion. And he was very unhappy. He’d been through a lot, he’s had a brain tumor, he’s 65 years of age, but given he’s 65, he’s actually in pretty good shape considering everything he’s been through. He was a little bit tricky to examine, but one of our orthoptists and myself, but we managed to establish that.
On right gaze he had no vertical squint, in primary position he had a moderate right hypertropia, and it increased on looking to the left. So that looks like a typical oblique muscle problem.
Sorry, this is the other way around, sorry. That should be right hypertropia over there. Anyway, it followed the three-step test. So please disregard this, it’s the wrong way round. This torsion is correct though, he had some torsion in primary position which increased on down gaze. He had about eight or 10 degrees of excyclotorsion. So you might say, is it unilateral, is it bilateral? Well, I’m not sure. So what do we do here?
Well he had a typical oblique muscle problem, so I thought for the vertical squint, I would weaken his inferior oblique. That should correct the vertical. But the inferior oblique probably has some excyclotorsion properties. It might help the torsion, I didn’t feel it was going to correct all that torsion and he was very symptomatic with his torsion, especially in down gaze. So I also did a right Harada-Ito at the same time.
This is a man that I operated on last Monday, so I don’t know how he’s turned out yet. It’s fingers crossed. This is the way I approached the problem, so there was a vertical squint, which followed an oblique muscle pattern so I operated on the inferior oblique for that. And there was a torsion problem for which I did Harada-Ito operation.
Right, so that’s the end of the didactic part of my talk. If you go into the American Academy Series, or other publications, you’ll find that there is a classification for fourth nerve palsies, the Knapp classification, where depending on which type of fourth nerve problems, there’s different approaches. I don’t tend to use that classification but it’s perfectly good. You use what works for you.
I approach each case, I probably effectively use the Knapp classification without calling it that because I evaluate each case on its merits and I work out what’s the right approach. Whether it’s inferior oblique weakening, superior oblique tuck, whether I need to add in inferior rectus recession on the opposite side, or whether I need to do a Harada-Ito. They’re all different, not just clinically different, but the patients are different with different expectations and different needs.
Always, when I’m carrying out squint surgery, I have a careful discussion with the patient, I try to get to know the patient and what kind of person they are, what their expectations are. And sometimes you have to manage expectations. We do that a lot. I can make this better, but I can’t cure it completely. That’s important, you might need more operations. So a standard part of my pre op discussion is about a 10-20% chance you might need another operation. I might not be able to fix this with one operation, I might not be able to fix it at all, even with more than one operation. So it’s important to have that discussion before the operation, not afterwards, I think.
Anyway, questions?
[Adedayo] So for the congenital types of palsies, in the comments, actually. That reviewing childhood photographs, hopefully reveals that the patient had always had some head tilt about them.
[Alan] I think that’s a very relative point. Most parents nowadays will have a smartphone and I ask them to go back and look through photographs, does the child always tilt the head a particular way? The old term for that is what’s called a FAT scan, F-A-T, or Family Album Tomography.
[Adedayo] (laughs) Yes. It’s very interesting. Any other questions, please? If you have any questions right now, Dr. Mulvihill has been talking about fourth nerve palsy. He’s been talking about some mnemonics: nothing-something-worse. Which I learned today. We’ve always been aware of the worse in opposite gaze, better on opposite tilt. And trying to remember which part of the muscle or the eye gaze involved.
Fourth nerve palsy, the tips you need, the impressions you need to be able to do a good job. Sometimes if you don’t get the right muscle or you don’t, you can get strong muscle movement is very important, as he has said. When you have evaluated the superior oblique and inferior oblique, you should be able to check and see whether it’s something that just the inferior oblique can handle, or something that you might need to add superior oblique tuck, or something you might need to do, torsion tests. Check the excyclotorsion and do the higher range. A question forward now, I’m sure many of the audience are quite convinced and maybe it’s clear to them on what to do when they see patients like this.
[Alan] It was a pleasure.
[Adedayo] Thank you.



December 11, 2020

Last Updated: September 12, 2022

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