Wagner: Today's topic is management of divergence insufficiency esotropia, which is often called age-related distance esotropia. I want to distinguish that from true divergence insufficiency, which often implies a neurologic cause. It still can in older individuals, but this is more specifically about a patient who developed the condition over time. An active and healthy 74-year-old woman presented with double vision at distance. This started intermittently, but became constant at distance after a few weeks and she still was only bothered slightly at near. It was particularly bothersome while driving and watching television. She had cataract surgery with intraocular lenses implanted in both eyes approximately 1 year before experiencing any double vision, so it didn't seem to be proximal to the surgery. On examination, she had a comitant deviation of 15 prism diopters at distance and a slight esophoria of 2 prism diopters at near, which did not seem to bother her as much as the distance diplopia. How would you treat this patient with an acquired comitant esotropia with a greater distance deviation?
Wang: Although your presentation indicates that this is a primary age-related phenomenon, I would first make sure that I'm not dealing with a sixth nerve palsy or some variant of a paretic lateral rectus muscle. I would make sure that in addition to the fact that she's comitant, she doesn't have any abduction deficiency or endpoint nystagmus. She has nothing in her history that would indicate something else is going on, such as headaches or any neurologic history that would indicate increased intracranial pressure. If all of those things were in place, I would continue to follow her. I probably wouldn't do neuroimaging, but I would if I had any suspicions. I would treat her distance diplopia with prisms.
Wagner: In this particular case, she didn't have an abduction deficit. Nerves were normal, but I think everyone would agree that this is the proper approach to this type of presentation. You're not really sure if it was isolated or not.
Guo: I agree. I would definitely want to make sure that the patient had a full eye examination and there were no other neurological issues. I would also make sure that the patient had no thyroid issues or myasthenia. If there were any suspicious findings, I would do neuroimaging to rule out incomitant esotropia. If all of the neurological and systemic work-ups are negative and the typical presentation was as you have mentioned, I would observe the patient. If she is symptomatic at distance, I would give her base-out prisms first.
Duss: I would also check for a sedimentation rate if she's in that age group and make sure she has no symptoms of giant cell. I'm seeing more of this type of patient in my own practice. Although we're apt to go straight to prisms, I've had a few patients who wanted to be spectacle free. I'm not opposed to the idea of surgery even with such a small angle deviation. This is a new presentation for this patient, so I agree that prisms are probably the first step. However, more of these patients who have specialty intraocular lenses or have refractive procedures along with their cataract surgeries want to be spectacle free. I have operated on several small-angle divergence insufficiency esotropias with good success.
Wagner: To follow-up on what you said about the frequency, the Rochester Epidemiology Project estimated divergence insufficiency esotropia to be present in approximately 10% of all adult strabismus cases. It's more common than you might think, and the median age at presentation was 74 years in the study that they mentioned. Do you try to correct the distance deviation completely and, if so, does that ever lead to an overcorrection at near?
Wang: You can cut Fresnel prisms and put them just in the distance. When they make a progressive lens, they can put the prism just in the distance, so you don't have to worry about tipping them over at near.
Duss: I've actually never converted them to an exotropia at near and I do usually prescribe the full distance deviation. In fact, I've started to measure both convergence and divergence amplitudes in these patients and you would be surprised how much convergence they have. They can actually tolerate significant base-out prism without overcorrecting. In my opinion, overcorrection is rare.
Guo: I have corrected fully for distance with prisms and my patients have done well without overcorrection at near.
Wang: One of the reasons I like to prescribe the prisms first is that I think the literature is confusing. On one hand, the etiology of this entity is that there's something wrong with the superior rectus–lateral rectus band that Joe Demer talks about and the lateral recti muscles become weak because they fall a little bit. I go along with that, and I don't think these things really resolve. But the literature talks about the natural history of this and a lot of cases resolve. I suspect that all of the ones that resolved were microvascular sixth nerve palsies where we don't see anything structural and they go away.
Duss: I agree with you. I don't see them go away.
Wang: Right. It's a proper time course for a microvascular sixth nerve palsy so that if you go to prisms first, you give them time to resolve if indeed they didn't have a primary degenerative adult divergence insufficiency.
Wagner: I think that makes a lot of sense because it is a mixed bag regarding etiology. There were some theories about a divergence center that is disrupted and it could be caused by a stroke or a neurovascular incident. Then you have the anatomic studies that you referred to that give a different cause and they're not all the same. I agree with Dr. Duss that in many of these patients you don't tend to overcorrect them even if you operate or use prisms to correct the distance deviation primary. Perhaps it is because throughout their lives they've had reasonable convergence and they can fall on the amplitudes later on. Let's say that you decide to perform surgery for whatever reason. What is your surgical approach?
Duss: There's obviously been some controversy over lateral rectus resection versus medial rectus recession and I have opted for a medial rectus recession. I think the biggest difference in these patients is the dose response curve. I have found studies saying maybe even twice as much as your normal surgical tables. I was hesitant to double my surgical tables, as I am sure most surgeons would be. I measure convergence amplitudes to determine each patient's proper surgical target. In the last several cases I've done, none of them have had postoperative diplopia or been overcorrected. I think that the previous studies on undercorrection of these patients actually just undertreated them. If you push them to the point of their diplopic breaking point and use that as your target angle, it can be successful.
Wagner: I assume you have not had trouble with overcorrection at near in these cases either.
Duss: Never. My dose response curve is not quite half of traditional Parks' tables, but it is definitely less. I've also found less prism diopter change per millimeter of recession for the smaller angles than for angles of greater than 20 prism diopters of esotropia.
Wang: I also do the medial muscles and I think you have to do a lot.
Guo: Most of my patients are happy with the prisms. There are a few patients who had the lateral rectus muscle resection with good results.
Wagner: We talked about the idea of sagging eye syndrome with the floppy lateral rectus muscles. When retinal surgeons do a retinal surgery or scleral buckles, they take the cotton tip applicator and they go far back on the muscle, not really meticulously dissecting, but just pushing back some of the connective tissue that's surrounding the muscle so they can get back to where they have to work. Given your theory is correct about these floppy muscles, you would think that you would induce a lot of strabismus from that procedure by disrupting the connective tissue band. Does that make sense?
Wang: Sometimes when they're doing that, the eye doesn't end up with perfect vision, but you certainly don't have to have perfect vision to have diplopia. You can have poor vision with diplopia. I don't think that's the issue. I think that most older people do not develop this syndrome and probably a lot of them have degeneration of their superior rectus–lateral rectus band. It may be that these are patients who have poor fusional vergences on top of it. Most people have good fusional vergences. When the retinal surgeons do that, they still have enough fusional vergences that the patients don't develop diplopia. I think that you can overcome the lateral rectus–superior rectus band issue if you have good fusional vergences. If you don't, then you develop this syndrome.
Guo: I agree. Some patients may have poor vision related to their severe retinal disease in only one eye. So diplopia may not be pronounced after retinal surgery. The other possible explanation is if a scleral buckle surgery is done in 180 or 360 degrees, connective tissue bands would occur in more than two quadrants, involving multiple rectus muscles. However, the superior-lateral rectus band occurs in only one quadrant in sagging eye syndrome. Good fusional vergence could also be the reason why patients do not have a typical or similar age-related distance esotropia syndrome after scleral bucking.
Wagner: I think you are onto something. Consider the patients who come to you with diplopia after scleral buckling. If you operate on them because they moved the insertion of the muscle itself, sometimes there's so much scarring around there, it's malpositioned and it's difficult to even isolate the muscle. I'm sure that happens with more people than present with diplopia, so I am assuming that they may have good fusional vergence that you can overcome.
Duss: I agree. Fusion is key.
Wagner: Thank you for participating.
This Eye to Eye session was conducted on May 22, 2019.