Botulinum Toxin Management of Essential Infantile Esotropia in Children

To do good research inthe field of strabismus, one must think fourth dimensionally—the fourth dimension being time. One needs to know not only theshort-term outcome of a given study, but also how those results hold up over time.Frequently manuscripts dealing with strabismus report data on patients who have beenfollowed up for a short while after surgery; the reader never learns how those samepatients fare as more time passes. Consequently, McNeer et al are to be heartilycongratulated for their article in this issue of the ARCHIVES. They report additionalfollow-up on a group of patients who were treated with bilateral botulinum toxin type Ainjections for infantile esotropia. (The initial report has been published.) At firstglance, the results they report seem good, so good in fact that the reader must answer thequestion:“Should botulinum toxin type A be thetreatment of choice for infantile esotropia?” As such, the article deserves to be read very critically. After such a reading, I believe the question remains unanswered because of some important unresolved issues.

McNeer et al report that 89% of patients had goodalignment with a follow-up of at least 1 year since the last injection. They note thatthese results are in sharp contrast with those of other reports of the use of botulinumtoxin type A in similar patient populations. They do not, however, speculate on why theirresults are so different from those of other investigators. Conceivably, experience andskill may explain the different results; however, this is unlikely. With this treatmentmodality, the main challenge for the surgeon is to create a pharmacologic paralysis of thetarget muscle. As long as the clinician is able to accomplish that, differences intechnique probably play a minimal role. One therefore must ask whether the patientpopulations being treated were different.

All investigators studying the treatment of infantileesotropia are plagued by the problem of inclusion criteria. It is generally agreed that togive a diagnosis of infantile esotropia, strabismus must have been present before 6 monthsof age. Unfortunately, clinicians rarely have the opportunity to see strabismic childrenthat young, and, consequently, researchers must rely on the history given by the parentsor observations made by primary care physicians. I am aware that the naysayers andpolemical critics of published studies are quick to point out that these 2 means ofdiagnosis may be flawed. I also realize this attitude can place an unfair burden on theresearchers. Nevertheless, the study by McNeer and coworkers raises serious questionsabout their patient population. They indicate a mean preinjection deviation of 33.4 prismdiopters with a range of 10 to 60 PD in their series of children with infantile esotropia.This is very low. In fact, 15 of 41 patients younger than 12 months of age hadpretreatment deviations of 25 PD or less. In my experience, it is rare for a child withinfantile esotropia to have a deviation less than 25 PD; I have a hard time acceptingtheir patient mix as representative of infantile esotropia. Von Noorden pointed out thatpPD to 62 PD, in my own previously reported series, the mean was 51 PD. Two explanationsfor this discrepancy seem possible. Perhaps many of the patients of McNeer and coworkersdid not have infantile esotropia despite the autors' efforts to keep the population pure.Inadvertent inclusion of patients with acquired esotropia would have skewed the resultstoward a better outcome. Alternatively, there may have been selection bias. The parents ofthe patients were given a choice as to whether they wanted incisional surgery or botulinumtoxin type A injection. We are not told anything about the number or characteristics ofthose patients whose parents elected incisional surgery. Were they possibly patients withlarger deviations? Such selection bias also could have influenced the results.

Of the patients studied, the deviations in 37 (49%)were well aligned horizontally (by the authors' criteria) with only 1 injection. Theremaining patients required multiple injections or their deviations were not acceptablyreduced. this is somewhat poorer than most reports on standard incisional surgery. What ismore noteworthy is that during a mean follow-up period of about 3 years, 11 patients (14%)required 3 or more procedures, and 6 (8%) had 4 or more. These numbers include onlyprocedures needed to obtain satisfactory horizontal alignment; they do not includeprocedures to correct dysfunction of the inferior or superior oblique muscles ordissociated vertical divergence. If one includes procedures needed to correct those 2disorders, the number of patients who need 3 or more procedures would undoubtedly behigher. The number of patients who need a large number of procedures with botulinum toxintype A injection is certainly higher than would be found in a series of patientsundergoing incisional surgery. Although McNeer et al point out that botulinum toxin type Ainjection is simpler and carries less risk than incisional surgery, I believe they haveoverstated the risks and complications of standard surgery. Also, McNeer et al indicatethat late referral compromises the results of incisional surgery in patients withinfantile esotropia. It is unclear to me why the factors that lead to delay of incisionalsurgery until an undesirable older age would not similarly result in delay of treatmentwith botulinum toxin type A injection. Indeed, almost half of the authors' patients wereolder than 12 months of age when treated.

Unfortunately, we are not told how many patients didnot meet the criterion of 12-month follow-up since the last injection because they neededongoing repeated injections. Certainly if there were many such patients, one would viewthese results differently.

In the end, it may be a matter of trade-offs, between which patients and clinicians may have a choice. Standard surgery may provide a higher success rate with a smaller number of procedures; botulinum toxin type A injection may be simpler and quicker, but require more interventions to reach the desired goal.

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