Although it is often considered a childhood condition, the incidence of strabismus is actually higher in adults. “Approximately 1 percent of children have strabismus,” says David Stager Sr., MD, who is in private practice in Plano, Texas. “In adults, the incidence is probably closer to 4 percent. Many of these cases are completely new entities, but, occasionally, it can be a recurrence of a childhood problem. I frequently tell parents that chances are 80 percent that it is fixed for a lifetime, but it’s not 100 percent. Many times, it can be decades before they start having a problem again.”
If an adult has new-onset strabismus, it is typically the result of a disease process or trauma. “There are myriad causes of adult strabismus, and the treatment often relates to the cause,” says Stephen P. Christiansen, MD, from Boston University School of Medicine. “It’s not uncommon for childhood strabismus to reappear in adults. Strabismus that patients were either able to control on their own or that was corrected with previous surgery may redevelop. Or, some patients may develop a problem for the first time that is related to their childhood misalignment. That’s a common scenario. Then, of course, adults are often prone to acquired forms of strabismus just because of the varying impact of disease and disease processes, such as thyroid eye disease. These are patients who have dysfunctional thyroid or abnormal thyroid function and then develop thickening and inelasticity of the extraocular muscles. Then, they develop vertical, horizontal or torsional strabismus.”
Additionally, there are patients who have strokes or ischemic disease that cause misalignment of the eye by affecting the cranial nerves that innervate the extraocular muscles, and these patients can have various forms of paralytic or paretic strabismus. “Then, there are patients who have trauma, and sometimes that trauma is iatrogenic,” says Dr. Christiansen. “For example, patients who had cataract surgery with various forms of retrobulbar anesthesia can develop muscle dysfunction and need realignment. There are patients who have had glaucoma surgery and have had seton implantation or scleral buckle placement that impacts the extraocular muscle rotation and function. Those patients may also develop strabismus.”
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| Figure 1. An adult strabismus patient pre- and postoperatively. |
He notes that the success rate of treatment is extremely high and offers vision improvement and psychosocial benefits. “Strabismus is not a cosmetic problem so much, because we usually think of a cosmetic condition as something normal that you would just prefer to change,” he says. “Strabismus is not a normal condition. We now know that there are functional benefits to treating strabismus that are not cosmetic. Many of these patients will develop binocular vision or depth perception. There has been a tremendous amount of work done also on the psychosocial benefits. A lot of these patients have improved self-esteem, chances at work and chances at marriage. They are very much negatively impacted by strabismus, and correcting strabismus can offer tremendous improvement in all of those areas.” According to a paper by Burt Kushner, MD, “Strabismus surgery in adults achieves satisfactory alignment with one operation in approximately 80 percent of patients, depending on the specific nature of the problem. Risks of adult strabismus surgery are relatively low, and serious complications are anecdotal and rare. Even if the strabismus has been long-standing, most adults will experience some improvement in binocular function after strabismus surgery. Consequently, adult strabismus surgery should not be considered merely cosmetic in most cases. In esotropic patients, this improvement typically takes the form of an expansion of binocular visual fields; however, some patients may also regain stereopsis. There are many psychosocial benefits to adult strabismus surgery. This is reflected in the finding that the majority of adults surveyed with strabismus would trade a portion of their life expectancy to be rid of their strabismus.”1
Non-Surgical Treatments
The treatment of strabismus depends on the severity, and management options range from observation to surgery. According to Michael Repka, MD, who is in practice at the Johns Hopkins Children’s Center in Baltimore, “For small amounts of strabismus, prism correction and other optical approaches would be attempted first. If that doesn’t work, depending on many factors or the situation for that patient, surgical approaches may be employed.”
Dr. Christiansen agrees. “Oftentimes, adults will develop small vertical or horizontal strabismus,” he says. “These patients can sometimes be best managed with either observation, if it’s not especially symptomatic, or with small amounts of prism placed in the glasses. If patients start developing a need for larger and larger amounts of prism to correct the alignment, they may develop spectacle distortion that they don’t like, and then you need to start thinking of other forms of treatment. My rule of thumb is that if they need more than 10 prism diopters in their glasses, they are probably going to be a surgical candidate at some point.”
Dr. Stager Jr. notes that certain types of orthoptic exercises or orthoptic training can be used to help give the patient better fusion. “Sometimes, we will just have to patch the eye to avoid diplopia if the patient is not a good candidate for other treatments. Often, in patients who are not good candidates for these other treatments, surgery can be an excellent option,” he says.
According to Dr. Christiansen, botulinum toxin A (BTX-A) is a fairly recent advance in strabismus surgery. “It can be used alone in some cases or, more commonly, as adjunctive treatment with standard muscle surgery,” he says. “BTX-A results in muscle paralysis that lasts for up to three months; however, the change in alignment of the eye may last much longer. There are certain forms of strabismus that can be successfully treated with BTX-A. More recently, bupivacaine has been proposed as a means of treating patients with strabismus. It is a local anesthetic that actually makes muscles bigger and stiffer. It is not widely used in the United States, but that may change if efficacy can be shown.”
In a recent study conducted in Brazil, a change in ocular motility was observed after 180 days of intramuscular injection of bupivacaine and botulinum toxin in horizontal extraocular muscles.2 In both botox- and bupivacaine-injected muscles, there was an increase of muscle thickness after 30 days of injection when measured by ultrasonography. This change was greatest on lateral rectus muscles after bupivacaine injection.
This study included eight patients (eight amblyopic eyes) in whom ocular motility was measured prior to injection and one, seven, 30 and 180 days after one injection of 2 mL of 1.5% bupivacaine and 2.5 U of botulinum toxin A in agonist and antagonist muscles, respectively. Muscle thickness was measured prior to injection and on days one, seven, and 30 after injection using 10-MHz ultrasonography.
The mean change in alignment was 10 prism diopters after 180 days. Using ultrasonography, an average increase of 1.01 mm in muscle thickness was observed after 30 days of bupivacaine injection, and an average increase of 0.28 mm was observed after BTX-A injection. A mean increase in muscle thickness of 1.5 mm was seen in lateral rectus muscles injected with bupivacaine.
Surgical Treatments
If the abovementioned treatment strategies do not achieve the desired result, surgery is the next step. “Surgical techniques to treat adults and children are largely the same,” Dr. Repka says. “However, many surgeons use adjustable sutures in adults that are not used in children. Adjustable sutures provide the ability to postoperatively fine-tune the alignment to the desired position.”
However, outcomes can be less predictable in adults than they are in children. “Most often, the techniques we use in adults are the same that we use in children,” says Dr. Christiansen. “However, in some cases, adult strabismus is complicated by abnormal extraocular muscle function, either because of inelasticity or because of paralysis. So, we have to adjust our techniques to the underlying pathology. Because of the unique pathology, and because many adults who have strabismus have had previous surgery, outcomes may be less predictable than in children. In hopes of improving outcomes in these situations, many surgeons use the adjustable suture technique, which allows the surgeon to position the operative muscle where it seems most appropriate. But, rather than securing the muscle permanently, the suture is tied in a temporary fashion, often with a slipknot that can be undone. The muscle position can be readjusted when the patient awakens from surgery. This adjustment can be done from six hours after surgery up to 24 hours after surgery and sometimes longer, depending on the adjustable suture technique. One potential drawback is that this technique requires a cooperative patient, so it is not often used in children.”
He adds that adult patients can usually expect a successful surgical outcome. However, there are some patients who have either such complex strabismus or have had a history of head injury that precludes adequate binocularity, and double vision can result. “As a whole, however, well over 80 percent of adult strabismus patients can be treated successfully,” says Dr. Christiansen. “Goals of surgery and definitions of success need to be discussed carefully with the patient preoperatively. For example, patients with paralytic or restrictive strabismus may not recover normal ocular rotations after surgery, which means that they will have some misalignment of the eyes in some positions of gaze.”
The goal for patients with the more complex forms of strabismus is to get them to fuse with a single image in a straight-ahead position and in the reading position. “That allows them to read, drive, and walk without double vision in these critical gaze positions,” Dr. Christiansen says. “Even with double vision in side gaze, however, many patients learn to adjust their head position, so that they can see singly. I counsel patients ahead of time that double vision may be treated successfully, but not completely. These patients learn to adjust pretty quickly and are much happier having straight eyes both for the cosmetic appearance and for the functionality of the depth perception they can re-establish.”
A number of studies have shown the efficacy of adjustable sutures in adults. For example, a recent Canadian study found that achieving the immediate target angle is the most significant factor in the success of strabismus surgery for exotropia and that adjustable suture surgery results in a larger number of patients achieving this target angle.3
The study included 353 patients who were older than 12 years and who underwent strabismus surgery with either adjustable or non-adjustable sutures. Mean follow-up was 13.9 months (range: four to 132 months). Patients who achieved the target angle immediately postoperatively had a higher success rate (83.6 percent) than patients who did not (63.7 percent), and when the target angle was achieved, the success rate was similar with adjustable (84.8 percent) and non-adjustable (80.9 percent) sutures. However, it is important to note that patients who underwent adjustable surgery obtained the target angle more often than those who underwent non-adjustable sutures (75.5 percent compared with 54 percent). The success rate for exotropia surgery was significantly higher when the immediate target angle was achieved (86.4 percent) than when it was not achieved (58.7 percent). However, a similar beneficial effect was not shown.
Additionally, a recent review of a large national private insurance database found that adjustable sutures were associated with significantly fewer reoperations in the first postoperative year for horizontal muscle surgery. Additionally, they were associated with more reoperations for vertical muscle surgery, but this observation was not statistically significant in the primary analysis after controlling for age.4
In this review, 526 of 6,178 surgical patients required and underwent a reoperation (8.5 percent). Of these reoperations, 8.1 percent were performed in patients who underwent adjustable suture surgeries and 8.6 percent were performed after conventional suture surgeries.
Of the 4,357 horizontal muscle surgeries, reoperations were performed after adjustable suture surgeries in 5.8 percent of cases and after conventional suture surgeries in 7.8 percent of cases. Of the 1,072 vertical muscle surgeries, reoperations were performed after adjustable suture surgeries in 15.2 percent of cases and after conventional suture surgeries in 10.4 percent of cases. Younger age (18 to 39 years) was associated with a lower reoperation rate, and significant multivariable predictors of reoperation for horizontal surgery were adjustable sutures, monocular deviation, complex surgery and unilateral surgery on two horizontal muscles. Adjustable sutures were not significantly associated with reoperation rates after vertical muscle surgery. REVIEW
1. Kushner BJ. The benefits, risks, and efficacy of strabismus surgery in adults. Optom Vis Sci 2014;91(5):e102-109.
2. Hopker LM, Zaupa PF, Lima Filho AA, et al. Bupivacaine and botulinum toxin to treat comitant strabismus. Arq Bras Oftalmol 2012;75(2):111-115.
3. Mireskandari K, Schofield J, Cotesta M, Stephens D, Kraft SP. Achieving postoperative target range increases success of strabismus surgery in adults: a case for adjustable sutures? Br J Ophthalmol May 19, 2015. [Epub ahead of print]
4. Leffler CT, Vaziri K, Cavuoto KM, et al. Strabismus surgery reoperation rates with adjustable and conventional sutures. Am J Ophthalmol 2015;160:385-390.
