Treatment of strabismus in adults with botulinum toxin A

The History of Botulinum Toxins in Medicine: A Thousand Year Journey

Botulinum toxin is one of the most potent and deadliest substances on earth. Because of its unique mechanism of action at the synaptic junction and the ability to precisely deliver the toxin locally to where it is needed, botulinum toxin has been used as an effective treatment for a plethora of diseases from head to foot, from chronic migraine to ankle spasticity. Unlike systemic drugs, botulinum toxin is delivered by injection to the site of disease. As we will see from the history of botulinum toxin, the ability to deliver the drug locally to minimize the amount of botulinum toxin needed and thereby minimizing systemic exposure has been key to its medical utility. Botulinum toxin was first approved by the US Food and Drug Administration in 1989 for the treatment of blepharospasm and strabismus, but the history starts long before this, with outbreaks of food poisoning in the tenth century. Importantly, the development of botulinum toxins for medical use continues today with the engineering of novel toxins to treat disease.

Management of Thyroid Eye Disease-Related Strabismus

Purpose:

To review various treatment methods in thyroid eye disease (TED) related strabismus.

Methods:

We searched in PubMed and Google Scholar and Ovid MEDLINE for keywords including TED-related strabismus, strabismus in thyroid-associated ophthalmopathy, Graves^' ophthalmopathy related strabismus or squint, and restrictive strabismus. Two expert strabismus specialists selected and evaluated the English articles that were related to our paper and had been published since 2000. Some articles were added based upon the references of the initial articles.

Results:

One hundred fifteen articles were found, 98 of which were mostly related to the topic of this review. Management of TED-related strabismus was reviewed and categorized in non-surgical and surgical. Botulinum toxin A (BTA) is a useful non-surgical management of strabismus in an active TED and residual deviation after strabismus surgery. Postoperative under-correction is relatively more common in TED-related esotropia. Lateral rectus resection and BTA are the options to manage the problem. Muscle rectus muscle resection should be performed after maximum recession of restricted muscles. It should be avoided on a restricted or enlarged muscle. Management of TED-related vertical deviation is challenging. In these cases, the surgical treatment selected depends on forced duction test (FDT) (pre and intraoperative), orbital imaging (which muscle is enlarged), and the amount of vertical deviation (in both down-gaze and primary position).

Conclusions:

TED-related strabismus needs careful evaluation and management to achieve optimal outcome. Different surgical and non-surgical options are available for intervention in TED-related strabismus.

The Use of Botulinum Toxin in Strabismus Treatment

There is a long and extensive experience with the use of Botulinum Toxin type A (BoNT-A) injection in the treatment of different types of strabismus and oculomotor palsies. The frequency of its use varies depending on the country and institution. It is a short procedure, may reduce general anesthesia exposure, causes minimal scarring compared to surgery, and can be proposed as an early treatment in unstable strabismus. Over many years, the experience of using BoNT-A indications has been refined and new applications have been reported. The use of BoNT-A in the postoperative period, after strabismus surgery or during surgery, can also be beneficial.

Botulinum toxin chemodenervation for childhood strabismus in England: National and local patterns of practice

Background

Botulinum toxin injection chemodenervation is a well-established intervention for adult strabismus, and has also been recognised as an effective alternative to routine incisional surgery for paediatric disease. We aimed to investigate the temporal patterns of practice, indications and outcomes of chemodenervation for paediatric strabismus at national and tertiary centre level.

Methods

Retrospective study using routinely collected patient data: Hospital Episode Statistics (HES) data were used to identify children undergoing non-incisional strabismus procedures in England from 2007 to 2016. Single–centre retrospective data on children undergoing botulinum toxin injections (Dysport^® 2.5 units/ 0.1ml) as an isolated intervention (not involving incisional procedures) was undertaken to identify indications and outcomes. Successful outcome was defined as deviation <11 prism dioptres (PD).

Results

Between 2007 and 2016, there was no increase in the proportion of childhood strabismus involving non-incisional procedures. Amongst 150 children undergoing chemodenervation for strabismus within the tertiary centre, the most common diagnoses were acute onset esotropia (n = 34), infantile esotropia (n = 16) and consecutive exotropia (n = 15). Median age at injection was 8.5 years (range 0.9–15 years), and median follow up 12 months (6 months—11 years). Success rates differed by diagnosis, from 66% (non or partially accommodative esotropia) to 0% (congenital cranial disorders). Adverse events were seen in 62/150, 41%, most commonly transient ptosis (39%, n = 58). Overcorrection was seen in 14/119, 13%. Mild subconjunctival haemorrhage (n = 2) was the only other adverse event.

Conclusions

Botulinum toxin for childhood strabismus has an acceptable safety profile, and considerable potential therapeutic benefit. However, nationally there has been no increased uptake of chemodenervation non-incisional procedures. Further prospective studies are necessary to understand the predictors of outcome within the separate clinical subgroups, to guide clinical decision making.

AbobotulinumtoxinA: A 25-Year History

During the late 1960s and early 1970s, Alan Scott showed that intramuscular injections of botulinum toxin (BoNT) corrected nonaccommodative strabismus without resorting to surgery. The UK doctors who trained with Scott soon realized the significant potential offered by BoNT type A as a therapeutic option for several difficult-to-treat diseases. This led to a collaboration between these pioneering clinicians and the Centre for Applied Microbiology and Research at Porton Down, United Kingdom, and, in turn, to the development and commercialization of abobotulinumtoxinA as Dysport (Dystonia/Porton Down; Ipsen Biopharm Ltd., Wrexham, UK). Dysport was approved in Europe for the treatment of specific dystonias in December 1990 and now has marketing authorizations in 75 countries. Since then, the use of BoNT in therapeutic and aesthetic indications has grown year-on-year, and continues to expand well beyond Scott's initial aim. For example, ongoing trials are assessing potential new indications for BoNT-A, including acne and psoriasis. Furthermore, a growing number of other BoNT products, often termed "biosimilars," together with innovative formulations of well-established BoNT types, are likely to reach the market over the next few years. This review focuses on the history of Dysport to mark the 25th anniversary of its first launch in the United Kingdom.

Clinical outcomes of botulinum toxin injection in patients with cerebral palsy and esotropia

PURPOSE

To assess the efficacy of botulinum toxin (Novotox) injection in patients with cerebral palsy (CP) and esotropia.

PATIENTS AND METHODS

In a non-comparative, prospective interventional case series botulinum toxin injection was done in 44 patients with CP and esotropia. A single dose of botulinum toxin was injected in both medial rectus muscles of all patients and was repeated in 12 patients. Angle of deviation within 10 prism diopters (PD) of orthotropia was defined as a successful outcome.

RESULT

Forty-four patients (21 males) with the mean age of 47.56 ± 35.86 months were included in the study. The mean esotropia in all patients was 52.27 ± 18.40 PD (25-123 PD). The range of follow-up was 12-24 months. Thirty patients (68.18%) were treated successfully one year after surgery. The rates of success, consecutive exotropia, and residual esotropia were 61.4%, 13.63%, and 25% in the last follow-up, respectively. The logistic regression showed statistically significant results between success result and lower age, higher pre-injection deviation, one month post-injection deviation, and severe ptosis. Complications included subconjunctival hemorrhage and ptosis.

CONCLUSION

Botulinum toxin injection is reasonably less invasive with light anesthesia, scar free, and a therapeutic alternative for the patient with esotropia and CP. Therefore, it can provide more possible surgical options in future.

Surgical dose-effect relationship in single muscle advancement in the treatment of consecutive strabismus

PURPOSE

To evaluate the dose-effect relationship for single muscle advancement in consecutive esotropia and consecutive exotropia.

METHODS

Medical records from 22 patients with consecutive esotropia (n = 11) or exotropia (n = 11) were retrospectively reviewed. All patients had undergone either single lateral rectus or medial rectus advancement surgery. The alterations in muscle position and the angle deviation were measured in millimeters and prism diopters (PD) and the change in deviation was determined by subtracting the postoperative angle of deviation at 1 week from the preoperative angle. To quantify the clinical effect of muscle advancement, the ratio of the change in muscle position to the change in visual angle deviation was calculated (ie, the surgical dose-effect relationship).

RESULTS

The mean deviation was 25.5 ± 10.4 PD preoperatively and 0 ± 6.9 PD at 1 week postoperatively. The success rate was 82% in the consecutive esotropia group and 91% in the consecutive exotropia group. The average correction ratio was 4.31 ± 0.96 PD/mm. In multiple regression analysis of total patients with consecutive strabismus and the consecutive esotropia group, the amount of muscle advancement and preoperative angle deviation were positively correlated with the correction ratio. In the consecutive exotropia group, there was no significant relationship between variables.

CONCLUSIONS

Single muscle advancement generally provides enough correction for most consecutive strabismus cases. Surgical dose-effect relationship increases with preoperative angle deviation and amount of muscle advancement. Surgeons should consider reducing the amount of muscle advancement in patients with larger angle deviations, especially patients with consecutive esotropia.

Acute effect of bupivacaine and ricin mAb 35 on extraocular muscle in the rabbit

PURPOSE

To identify acute histologic change of extraocular muscles induced by bupivacaine or ricin mAb 35 injection.

METHODS

The superior rectus and inferior rectus of white rabbits were injected with bupivacaine (0.4 mg in 0.3 ml) or ricin mAb 35 (0.2 microg/kg in 0.3 ml). After 1, 2, and 4 weeks, the rectus muscles were harvested, and postinjection changes in the muscle layers were examined histopathologically.

RESULTS

Bupivacaine and ricin mAb 35 induced myotoxic changes in both the orbital and the global layers. However, the inflammation and the myofiber destruction produced by bupivacaine injection was localized to the injection site, which compared with the diffuse change induced by ricin mAb 35. Inflammation reduced rapidly over 2 weeks. Regenerating myofibers with a central nucleus were found at 1 week after injecting these myotoxins. Four weeks after injection, the acute changes induced by these two toxins respectively were much recovered with prominent myofiber regeneration.

CONCLUSIONS

We found that extraocular muscle has a superb ability to recover from the acute injury induced by bupivacaine or ricin mAb 35, and the two myotoxins induce unique damage including the predilection of muscle layers and duration of damage persisted. Further investigation about the functional change during recovery from the myotoxin-induced injury of extraocular muscles is needed.

Effects of botulinum A toxin injection on the extraocular muscle fiber layers: comparison between subtenon injection and intramuscular injection

PURPOSE

To compare the morphological changes following injection of botulinum A toxin to the extraocular muscle fiber layers with those following injection to the subtenon intramuscular system.

METHODS

Twelve New Zealand white rabbits were divided into two groups. In the first group (six rabbits), four received injections of 10 units of botulinum A toxin into the subtenon space of the superior rectus muscle OD, and the same dose of botulinum A toxin was injected directly into the superior rectus muscle OS. The other two rabbits in the first group were labeled as control animals; 0.1 ml of normal saline was injected into the subtenon space OD, and direct intramuscular injection was performed on the opposite eye. The animals in the first group were killed after 4 weeks to measure the average diameter of the muscle fibers in both the orbital and global layer. In animals of the second group (six rabbits), the same procedures were performed and the animals were killed 12 weeks after treatment.

RESULTS

The average diameter of muscle fibers in both the orbital layer and global layer was markedly reduced in all of the botulinum A toxin-injected groups at 4 weeks after treatment compared with the controls. There was no difference in the average diameter of the muscle fibers between the orbital layer of the subtenon-injected group and that of the intramuscular-injected group at 4 weeks after treatment, but the average diameter of the muscle fibers in the global layer was significantly reduced in the intramuscular-injected group compared with the subtenon-injected group at 4 weeks after treatment. At 12 weeks following treatment, there was no difference in the average diameter between the botulinum A toxin-injected group and the control group regardless of where the toxin was injected.

CONCLUSION

Subtenon injection of botulinum A toxin induced similar morphological changes as direct intramuscular injection in the extraocular muscle fiber layers. These results suggest the possibility of clinical applications of subtenon botulinum A toxin injection for the treatment of strabismus.

The role of Botulinum toxin in management of acute traumatic third-nerve palsy

PURPOSE

To study the effect of botulinum toxin A injection in the management of paralytic exotropia resulting from acute traumatic third (oculomotor) nerve palsy.

METHODS

Nine patients with acute traumatic partial third-nerve palsy of less than 2 months' duration were treated by injection of botulinum toxin A into the ipsilateral lateral rectus muscle. The horizontal deviation angles before and after the injections were recorded. A distance exotropia of less than 10(Delta) or absence of diplopia in the primary position at the last follow-up was defined as recovery.

RESULTS

The mean preinjection deviation in the primary position was 48.3(Delta) of exotropia, and the mean postinjection deviation in the primary position was 14.2(Delta) at the last follow-up. Seven patients experienced recovery and regained single binocular vision in the primary position. The overall recovery rate was 77.8%. Two patients did not recover and subsequently underwent strabismus surgery.

CONCLUSIONS

Patients with acute traumatic partial third-nerve palsy treated by injection of botulinum toxin A in the lateral rectus muscle showed marked recovery when injection was performed within 2 months of the onset of palsy. Botulinum toxin injection into the lateral rectus muscle may provide temporary relief of symptoms in some patients and seems to be a useful treatment option in cases of acute traumatic third nerve palsy in the short-term.

Botulinum toxin treatment of extraocular muscles in rabbits results in increased myofiber remodeling

PURPOSE

Botulinum toxin A (Botox) is commonly used for strabismus treatment. Although other muscles atrophy after intramuscular injection with Botox, extraocular muscles (EOMs) do not. A continuous process of myonuclear addition in normal uninjured adult myofibers in rabbit EOMs was studied. In this study, the effect of Botox-induced muscle paralysis on myofiber remodeling in adult EOMs was examined.

METHODS

The superior rectus muscles of adult rabbits were each injected with 5 units of Botox. The contralateral muscle received injections of saline only. Bromodeoxyuridine (BrdU) was administered for various periods after Botox treatment, followed by various BrdU-free periods. Myonuclear addition, the number of BrdU-positive satellite cells, and the number of MyoD-positive satellite cells were quantified, as were alterations in expression of immature myosins.

RESULTS

Intramuscular injection of Botox resulted in a significant increase in both the number of BrdU-positive myonuclei and satellite cells. MyoD expression in both satellite cells and myonuclei was significantly increased after Botox injection in EOMs. In Botox-treated EOMs, an increased number of myofibers positive for the neonatal myosin heavy chain (MyHC) isoform was detected in the orbital layer.

CONCLUSIONS

Botox-induced EOM paralysis resulted in a significant short-term increase in satellite cell activation and myonuclear addition in single myofibers in adult rabbit EOMs compared with control muscles. The appearance of MyoD-positive myonuclei suggests that protein synthesis becomes upregulated after Botox injection, and this, in turn, may help explain the minimal effects on myofiber size in EOMs after Botox injection. Understanding the effect of Botox on satellite cell activation and myonuclear addition in existing myofibers may suggest new ways to maximize the clinical effectiveness of Botox in patients with strabismus.

A single transcutaneous injection with Botox for dysthyroid lid retraction

PURPOSE

To evaluate the safety and efficacy of injections with botulinum toxin type A (BTTA,Botox), given transcutaneously, in the treatment of upper lid retraction associated with thyroid eye disease (TED).

METHODS

A total of 15 patients (21 eyes) with a stable (TED) condition, and a euthyroid state, were enrolled into the study. There were 12 females and three males from ages 23 to 52 years. A single injection, at the centrally superior tarsal border transcutaneously, aiming at the levator aponeurosis and Müller muscle, was administered into each eyelid with 5-6 U of Botox. All patients were followed regularly for 4-6 months. Any complications, such as ptosis, diplopia, pain,or lid ecchymosis were recorded.

RESULTS

All patients, except one, experienced much reduction of palpebral fissure. The mean difference of MRD1 between pre- and postinjections of Botox at the first week was -3.1 mm, and the effect remained, at least, for 2 months. There were temporary complications of ptosis in three patients and vertical diplopia in two patients, lasting 3-4 weeks.

CONCLUSIONS

A single transcutaneous injection with Botox for the treatment of thyroid lid retraction is safe and effective. Some minor complications may occur, such as ptosis and diplopia; however, it may offer an alternative and temporary method for patients with dysthyroid lid retraction, who are waiting for a staged operation of either an orbital decompression or a strabismus surgery or both.

Efficacy and complications of dose increments of botulinum toxin-A in the treatment of horizontal comitant strabismus

PURPOSE

To investigate the efficacy and complications associated with dose increments of botulinum toxin-A (BTA) for comitant horizontal strabismus patients.

METHODS

Twenty-five esotropic (ET) and 45 exotropic (XT) patients received 2.5-20 U of BTA injection. Parameters for achieving less than 10 prism dioptres (pd) of horizontal deviation and percentage correction of the pretreatment deviation were assessed for injections of less than 10 U and more than 10 U of BTA. Induced ptosis and vertical deviation were examined within and after 6 months of follow-up.

RESULTS

The mean pretreatment deviations were 38.6 +/- 2.5 pd and 37.6 +/- 1.9 pd for the ET and XT groups, respectively. After receiving 1.6 and 1.5 injections on average, improvement to less than 10 pd at the primary position occurred in 32% of ET and 22% of XT patients; the difference was not statistically significant. The percentage corrections of the ET patients were 41.4 +/- 9.3% and 36.9 +/- 5.6% in those treated with less than 10 U and more than 10 U of BTA respectively; the difference between the two groups was insignificant. For the XT patients the values were 42.1 +/- 7.4% and 28.9 +/- 3.5% respectively, which also were not statistically significantly different. Frequency of induced ptosis was more common in ET than XT patients (p = 0.01) and this difference was more pronounced with increased doses of BTA (7.7% in ET and 5.3% in XT patients with less than 10 U of BTA, and 24.0% in ET and 4.3% in XT patients with more than 10 U of BTA). Ptosis resolved completely within 6 weeks in all cases. Induced vertical deviation with less than 10 U of BTA was encountered in one case of ET (11.1%, 9 pd) and in another case of XT (8.3%, 4 pd), increasing to 60.0% (2-20 pd) and 38.8% (4-16 pd) respectively with more than 10 U of BTA injection. In about a year, induced vertical deviation resolved in approximately 40%, and decreased in 30% of the cases.

CONCLUSION

Increasing the dose of BTA is clinically effective in larger deviations, although statistically indifferent, especially in ET compared with XT. However, an increased dose is accompanied by increased incidence of induced ptosis and vertical deviation. Ptosis is temporary, but vertical deviation may persist for a long time and may present a cosmetic problem for some patients when more than 10 U of BTA is used.

What is the role of botulinum toxin in the treatment of dysthyroid strabismus?

BACKGROUND

Botulinum toxin A has been used in the treatment of dysthyroid strabismus primarily as a temporary measure during the active phase of the disease. We report on our experience with 65 patients.

METHOD

We review the records of 65 patients with dysthyroid strabismus who were treated with botulinum toxin A at Moorfields Eye Hospital between 1984 and 1996.

CONCLUSIONS

Patients with a short duration of relatively mild dysthyroid strabismus have a chance of long-term benefit with botulinum toxin A. There is little use for botulinum toxin A in cases of severe dysthyroid disease.

Long-term results of botulinum toxin in consecutive and secondary exotropia: outcome in patients initially treated with botulinum toxin

INTRODUCTION

Long-term ocular alignment can be difficult to achieve in patients with consecutive and secondary (sensory) exotropia, and botulinum neurotoxin A (BTXA) is a recognized alternative to surgery in this group.

PATIENTS AND METHODS

We reviewed the results of 44 patients aged 15 to 77 years (mean 31 years) who underwent their first BTXA injections from 1989 to 1990. In 30% of cases the choice of toxin treatment was made by the patient. In the remainder BTXA was recommended by the clinician to assess the risk of postoperative diplopia. Thirty-three patients (75%) were consecutively exotropic and 68% of patients had had previous strabismus surgery. The mean preinjection deviation was 41 delta of exotropia (range 12 to 85 delta exotropia) and the minimum mean angle change after 1 injection was 27 delta (range 0 to 57 delta). The average number of injections was 3 (range 1 to 17).

RESULTS

Of the patient group, 59% went on to strabismus surgery, 14% continued to attend for maintenance treatment, and 9% were discharged with a small, stable deviation. The remainder were either followed up elsewhere or failed to reattend.

CONCLUSIONS

Botulinum toxin appears to be a satisfactory treatment for constant exotropia in patients at risk of postoperative diplopia who have undergone multiple operations but, because more than half the group went on to surgery, surgery as a first therapy may be preferable in uncomplicated cases.

Large-angle exotropia corrected by intraoperative botulinum toxin A and monocular recession resection surgery

PURPOSE

Surgical correction of large-angle exotropia, greater than 70 PD, traditionally requires operating on three or four horizontal muscles. However, in secondary exotropia from monocular visual loss, it is advisable to operate only on the eye with poor vision. We used intraoperative botulinum toxin as an adjunct to the monocular recession-resection procedure for large-angle sensory exotropia, therefore operating only on the visually impaired eye.

METHODS

Three patients underwent monocular recession (10 mm) and resection (10 mm) along with intraoperative botulinum toxin A injection of 10 units into the recessed muscle. All had desired cosmetic repair of long-standing large-angle exotropia (range 100 to 110 PD) with amblyopia and vision worse than 20/200 in the deviated eye.

RESULTS

Within 4 days after operation all patients demonstrated maximal paresis of the lateral rectus muscle. This lasted 8 to 12 weeks and resulted in stable orthotropia at 2.5 years in case 1 and stable 8 PD exotropia at 4 years in case 2. The third case demonstrated a stable 18 PD exotropia by 7 months with a satisfactory cosmetic result.

CONCLUSION

This technique provides an alternative for the surgical correction of large-angle exotropia by operating only on two horizontal muscles. In sensory exotropia it also avoids subjecting a normal eye to an operative risk.

Dissociated effects of botulinum toxin chemodenervation on ocular deviation and saccade dynamics in chronic lateral rectus palsy

AIM

Changes in saccade velocity/amplitude characteristics (main sequence) and attenuation of distance esotropia in response to botulinum toxin (BTX-A) chemodenervation of the antagonist medial rectus were studied in a group of nine patients with chronic lateral rectus palsy.

METHODS

Serial measurements of ocular deviation and infrared oculograms of saccadic eye movements to targets at 5 degrees-20 degrees of lateral gaze were made before injection and at 2, 4, 8, 16, and 20 weeks after injection.

RESULTS

At 2 weeks after injection, the ocular deviation changed by a mean of 34.5 prism dioptres and the 5 degrees and 10 degrees adduction saccades were significantly slowed (p < 0.02 Wilcoxon signed rank test). By the second examination, however, the adducting saccade peak velocity had returned to normal while the mean ocular deviation remained significantly changed (p = 0.01 Wilcoxon matched pairs). By 20 weeks the mean ocular deviation was not significantly different from that before injection (p = 0.14 matched pairs).

CONCLUSIONS

The ocular realignment caused by BTX-A may persist after saccadic function has been restored. This may be because toxin may have a more profound and long lasting effect on the orbital singly innervated fibres which are active tonically at rest to hold gaze whereas there is relative sparing of the additional motor units recruited during fast eye movements.

Botulinum toxin management of childhood intermittent exotropia

OBJECTIVE

Intermittent exotropia is a common form of childhood strabismus that has a late onset and presents a difficult and frustrating management dilemma. Surgical treatments have a high recurrence rate, and multiple surgeries often are required to achieve a desirable motor outcome. This study presents long-term observations on the use of botulinum toxin for the treatment of intermittent exotropia in children.

DESIGN

This study is a nonrandomized, case-controlled study of consecutive pediatric patients who had intermittent exotropia.

PARTICIPANTS

Thirty-two neurologically normal children ranging from 3 to 144 months in age were diagnosed with intermittent exotropia with a minimum distance deviation of 15 prism diopters (PD).

INTERVENTION

Simultaneous bilateral injections of 2.5 units botulinum toxin type A were made into the lateral rectus muscles with the patient receiving nitrous oxide-ethrane inhalation anesthesia. Patients were observed for 12 to 44 months after the initial injection.

MAIN OUTCOME MEASURES

A satisfactory outcome was considered to be stable binocular alignment of the eyes to an orthophoric range of +/-10 PD.

RESULTS

Bilateral lateral rectus muscle injections of botulinum toxin were effective in reducing the mean preinjection deviation of -29 PD to an average exotropic angle of -6 PD. Stable orthophoria (+/-10 PD) was achieved in 22 patients (69%). Overall, male patients required significantly fewer injections than did female patients. All patients between 24 and 56 months of age, irrespective of gender, required only a single bilateral injection to achieve a favorable motor outcome.

CONCLUSIONS

Botulinum toxin is at least as effective as surgical outcomes reported previously for the treatment of intermittent exotropia in children. This treatment method is particularly effective in children between 2 and 4.5 years of age irrespective of the initial strabismic angle and is not associated with any secondary abnormalities.

Factors influencing success and dose-effect relation of botulinum A treatment

Botulinum toxin type A (BTA) treatment is an alternative to strabismus surgery. In this retrospective study the data on 45 esotropic and 49 exotropic patients with concomitant strabismus who were treated with BTA were analysed for dose-effect relationship, the effect of repeat doses and amblyopia on success of botulinum treatment. The esotropic patients were treated with a total of 80 and exotropic patients with 91 injections. The deviations were corrected within 5 degrees of straight in 33% of esotropic and 18% of exotropic patients. In esotropic patients the effect was dose dependent. This relation was not shown in exotropic patients. The repeat doses of BTA corrected the deviation to the same extent as the primary ones for both esotropic and exotropic patients.

Strabismus after retinal detachment surgery: etiology, diagnosis, and treatment

Between 5% and 25% of patients may experience persistent diplopia after surgery for retinal detachment. The complexity of the presentation poses a distinct challenge to both the retinal and the strabismus surgeon. Careful evaluation to determine factors contributing to the strabismus and assessment of fusional capabilities are essential before treatment. A combination of the appropriate surgical approach with nonsurgical adjuncts such as prisms or botulinum toxin is often successful in relieving symptoms.

The role of botulinum toxin in third nerve palsy

Isolated third nerve paresis is a rare diagnosis among patients presenting to the Botulinum Toxin Clinic at Moorfields Eye Hospital. Ten patients with this diagnosis are reviewed in this study. Head trauma is a common cause of third nerve palsy and is often severe enough to cause damage to fusion potential. If fusion is present and there is adequate adduction of the divergent eye, then botulinum toxin injection of the lateral rectus may induce long-term control of the ocular deviation. Three of the four patients who experienced long-term control of their ocular deviation following toxin injection shared these features. Toxin injected into the lateral rectus did not, however, reliably assess medial rectus function and therefore predict the outcome of horizontal squint surgery. Reasons for this are discussed.

Binocular diplopia in unilateral aphakia: the role of botulinum toxin

We have treated 12 unilaterally aphakic patients, with a manifest squint and binocular diplopia, with botulinum toxin injection to the appropriate horizontal rectus muscle, in an attempt to reduce the angle of squint and thereby resolve the diplopia. In all cases a short-term reduction in the angle of squint was achieved. In nine patients, whose aphakia was corrected with a contact lens, and eight of whom had had their lenses removed because of trauma, this reduction was only temporary. In three patients, however, who had had a non-traumatic cataract removed, replaced with a posterior chamber implant, control of the deviation was maintained long after the acute effect of the toxin had disappeared, with the development of coarse binocular single vision, a fusion range, and abolition of all diplopia. The possible reasons for these different responses are discussed and it is suggested that in cases of binocular diplopia following lens extraction, botulinum toxin treatment should be considered prior to any extraocular muscle surgery, as temporary reduction of the deviation may be sufficient to allow recovery of binocular single vision.

Use of botulinum toxin in strabismus after retinal detachment surgery

Botulinum toxin was used to treat 20 patients with strabismus after retinal detachment surgery. Preinjection motility deviations ranged from 10 to 60 prism diopters (D). Postinjection deviations ranged from 0 to 20 prism D, with 75% being 10 D or less. Eighty-five percent achieved fusion that persisted, with 73% requiring only one or two injections. Only muscles in the eye that had undergone retinal reattachment surgery were injected. The average period of follow-up was 12 months. Complications were rare and all resolved spontaneously. Botulinum toxin appears to be useful as a primary treatment modality for persistent strabismus following retinal detachment surgery, possibly obviating the need for complicated strabismus surgery.

Succinylcholine-stimulated muscle tensions following botulinum injection in the domestic cat

Succinylcholine (SCh) selectively stimulates, and can therefore selectively assay, the multiple innervated (MI) fiber system of the extraocular muscles. Since botulinum-A toxin has been observed to induce changes in eye position in humans, SCh was used to assess the effect of botulinum-A on the SCh-sensitive MI fibers of extraocular muscles. Intravenous SCh infusion (40 micrograms-1 kg-1 min-1 was performed in the anesthetized domestic cat. Thirty-eight infusions were performed in 19 normal controls, measuring the peak tensions generated in the four horizontal and four vertical rectus muscles. Succinylcholine-stimulated muscle tensions (SSMT) were then repeated in nine animals, 4 weeks and 10 weeks following injection of botulinum-A toxin into both medial rectus muscles. Mean peak SSMTs were unchanged at 4 and 10 weeks following botulinum injection when compared to controls. We propose that botulinum chemo-denervation has no acute or chronic effect on the MI SCh-sensitive muscle fibers of the medial recti of the domestic cat. This lack of effect on the postsynaptic MI fibers indirectly supports light and electron microscopic studies which show changes predominantly in the singly innervated (SI), rather than the MI fibers following botulinum injection. Mean peak SSMTs were also greater for medial and superior rectus muscles compared to lateral and inferior recti respectively, suggesting a greater number or proportion of MI fibers in medial and superior recti.

Botulinum treatment of childhood strabismus

Four hundred thirteen children ranging in age from 2 months to 12 years were treated for strabismus by botulinum injection of extraocular muscles. An average of 1.7 injections per patient was given. Follow-up at an average of 26 months after the last injection (minimum, 6 months) was available on 362 children (88%). The frequency of correction of 10 prism diopters (PD) or less in various groups of strabismus cases was: all 362 cases, 61%; all esotropia, 66%; infantile esotropia, 65%; and exotropia, 45%. Smaller deviations (10-20 PD) were more frequently corrected (73%) than were larger deviations (20-110 PD, 54%). The frequency of correction to 10 PD or less of previously operated cases was not different from that of unoperated cases. There was no globe perforation, amblyopia, or visual loss produced by the injection treatment in this series.

Early and late botulinum toxin treatment of acute sixth nerve palsy

Ten patients with sixth nerve palsy were treated with botulinum toxin injection to the antagonist nonparetic medial rectus. All patients were followed for a minimum of 14 months after the last injection. Six patients were treated within eight weeks of the onset of the palsy. Within a few days five of the six gained fusion, without the necessity of a marked head turn and none complained of confusing reversal of diplopia. The same five recovered full function. Four patients with no medial rectus contracture on forced duction testing were treated six months or longer after the onset of the palsy and none recovered full function. One of the four patients was permanently over-corrected despite persistent weakness of the lateral rectus. This preliminary report suggests that early botulinum toxin injection of patients with recent onset (acute) sixth nerve palsy is beneficial. Since some patients may recover spontaneously a randomised double-blind study is necessary to more precisely determine the effectiveness of this form of therapy. Botulinum toxin does not appear to be effective in facilitating recovery in those cases with poor lateral rectus function six months or longer after the onset of the palsy, even when there is no contracture of the medial rectus.

Management of strabismus with botulinum A toxin

Three hundred eight patients with strabismus were treated with botulinum A toxin (Oculinum) chemodenervation; 153 were followed by the authors for at least 6 months. In this study group, 97 received botulinum A toxin injections as the primary method of treatment of their ocular deviation. Fifty-six received injections after traditional extraocular muscle surgery. Botulinum A toxin was useful for management of patients with recent surgical overcorrections and for management of some patients with sixth cranial nerve palsy. Chemodenervation of an extraocular muscle was not as successful as traditional strabismus surgery for treatment of infantile esotropia and other comitant deviations. Botulinum A toxin injection was ineffective in patients who had restrictive strabismus. This drug has limited application in the management of patients with strabismus.

The role of botulinum toxin in the management of sixth nerve palsy

Fifty-five patients with sixth nerve palsy have been treated with Botulinum toxin injection to the antagonist medial rectus, either in isolation or in combination with rectus muscle surgery. Forty of these patients (72 per cent) obtained significant benefit from injection at some stage in their management. Botulinum toxin has a major role in conjunction with transposition muscle surgery for the treatment of complete unrecovered sixth nerve palsy. In less severe paresis, a functional cure may be obtained in a significant number of cases with the use of Botulinum toxin alone, 37 per cent in this series. No serious complications were observed. In view of the safety of this procedure it is reasonable to consider an injection of Botulinum toxin in any adult patient with a persisting sixth nerve palsy.

Effect of botulinum toxin on extraocular muscle proprioception

Injections of botulinum toxin type A (BoTox) in one extraocular muscle (EOM) induce long lasting paretic lengthening of the muscle permitting realignment to occur in strabismus, while eye movements appear to be unaffected after the transitory period of induced paresis. It has been hypothesized a BoTox-induced change in the spindle discharge of EOMs to explain the effect in EOM length. In decerebrate lambs and goats, first order neurons of eye muscle spindles were identified in a cellular pool located in the medial dorsolateral portion of the semilunar ganglion. The belly of the muscle to which the recorded unit belonged was infiltrated with BoTox. A decrease in afferent discharge of the spindle and in its stretch sensitivity was observed. This effect began 10-15 minutes after the injection. There was no corresponding decrease in muscle tension during the first 45 minutes. This finding suggests that the block of release of acetylcholine at motor endings is earlier and more efficacious in gamma- than in alpha-motoneurons. As a result of the proprioceptive input reduction, an unbalance between the agonist and antagonist muscles should occur favouring the ocular realignment.

Treatment of sixth nerve palsy in adults with combined botulinum toxin chemodenervation and surgery

This study reports the results of treating unrecovered sixth nerve palsy in adults with a combination of botulinum toxin and surgery. Twenty-two adults, 11 with unilateral and 11 with bilateral unrecovered sixth nerve palsy, were treated with injections of botulinum toxin to the contracted medial rectus followed by transposition surgery to the vertical rectus muscles. This management technique produced a satisfactory reduction in esotropia, averaging 46 prism diopters (PD), comparable with that achieved by conventional surgery in other series. The advantages of this form of treatment are discussed.

Experimental paralysis of tensor veli palatini muscle

In an effort to study the effects of experimental paralysis of tensor veli palatini (TVP) muscle on Eustachian tube (ET) function and middle-ear (ME) status, botulinum toxin A (Oculinum) was injected into the TVP muscles of 8 Rhesus monkeys. Tubal function was tested longitudinally in 2 animals with tympanostomy tubes using the forced-response test, while in the remaining 6 animals; ME condition was documented daily using tympanometry. The postinjection tubal function was characterized by abolished active muscular function and decreased closing pressure. Activity associated with tubal dilations gradually reappeared by the fifth week. The lack of lumen constrictions following injection suggested that the TVP muscle is the cause of constriction as well as normal dilation. In 6 animals with intact tympanic membranes, 10 of the 12 ears developed flat tympanograms associated with otitis media with effusion (OME) within 8-30 days of injection and serous effusions were recovered by tympanocentesis in seven ears. These results show that a non-traumatic reversible functional obstruction of the ET was created by injecting botulinum toxin A into the TVP muscle. This functional obstruction was associated with the development of high negative ME pressure and serous effusion.

Neurotransmitter release is blocked intracellularly by botulinum neurotoxin, and this requires uptake of both toxin polypeptides by a process mediated by the larger chain

Botulinum neurotoxins (types A and B), which are microbial proteins consisting of two disulfide-linked chains, inhibit specifically and with high potency the release of acetylcholine from peripheral nerve terminals. As a prerequisite for a long-term development of effective treatments for botulism, the internalization and inhibitory action of the toxin and its constituent chains were examined by electrophysiological methods at identified synapses in Aplysia preparations that allow both intracellular and bath application of the neurotoxins. Intracellular recordings from cholinergic cells of the buccal ganglion demonstrated that extra- or intracellular application of low doses of botulinum neurotoxin results in a specific blockade of evoked transmitter release, without changing the quantal size; an intraneuronal site of action has thus been established. In contrast, release from noncholinergic neurons of cerebral ganglion was prevented by the neurotoxin only after injection into the cell. Purified preparations of the individual renatured chains, shown to be nontoxic in a mouse bioassay, failed to affect acetylcholine release when applied extra- or intracellularly. However, inhibition of release was observed after intracellular administration of both chains or when the light chain was injected and the heavy chain was bath-applied. These findings show that both chains are required on the cytosolic side of the neuronal plasma membrane for expression of toxicity and that the cholinergic specificity of the neurotoxin is attributable to its heavy chain, which mediates targeting and subsequent neuronal uptake.

Botulinum toxin A-induced protective ptosis in corneal disease

Botulinum toxin A produces a temporary, flaccid ptosis when injected into the levator palpebrae superioris muscle. The resulting protective ptosis was used to aid healing in 21 cases of indolent ulceration, and, prophylactically, in 4 cases of neuroparalytic keratitis. Of the indolent ulcers, 90% healed completely. In all but one case, the cornea was covered completely by the lid and complete ptosis was produced in 75% of cases in an average of 3.6 days, lasting for 16 days on average before recovery began. Recovery of levator function was complete in 8.5 weeks on average. Superior rectus underaction was seen in 68% of cases but this recovered completely in all cases in an average of 6 weeks. Impression cytology showed a trend toward normal conjunctival morphology as healing progressed.

Botulinum toxin treatment of acute sixth and third nerve palsy

Thirty-four patients with acute sixth nerve palsy and nine patients with acute third nerve palsy were treated with botulinum toxin injection to the antagonist, nonparalytic horizontal rectus muscle. In a control group of 52 patients with acute sixth nerve palsy not treated with botulinum in the acute stage, only 16 (31%) recovered spontaneously and did not require surgery. Twenty-two of the 31 surviving patients who could be followed with acute sixth nerve palsy had lateral rectus recovery and surgery was avoided. Four required prisms in their glasses to obtain fusion. Nine patients developed chronic sixth nerve palsy and required surgery. In this group of acute sixth nerve palsy patients, eleven were bilateral. Seven of these eleven developed chronic sixth nerve paralysis, and required strabismus surgery. This suggests the prognosis for recovery following botulinum treatment in cases of acute bilateral sixth nerve palsy is not as good as in the unilateral cases. Botulinum toxin treatment does not appear to be effective in chronic sixth nerve palsy, as judged by results of treatment in one patient known to have a chronic palsy. Nine of nine patients with acute third nerve palsy had medial rectus recovery with fusion horizontally in primary gaze. None have required surgery. Only four of nine showed improvement in vertical rotations. The remaining five patients avoid vertical diplopia by a compensatory chin position. Botulinum toxin treatment of patients with acute sixth and third nerve palsy appears beneficial. However, since some in this group of patients may recover spontaneously, a randomized, double-blind study may be necessary to more definitively determine the effectiveness of this therapy.

Paralytic strabismus: the role of botulinum toxin

Five adults with acute extraocular muscle palsies followed by limited recovery of muscle function were treated with injections of botulinum toxin A to the ipsilateral antagonist of the affected muscle. Three were cases of unilateral sixth nerve palsy, one of bilateral sixth nerve palsy, and one of third nerve palsy. After a period of paralysis, during which the strabismus was overcorrected, the injected muscle recovered and binocular sensory and motor functions were restored and have been maintained for periods of up to 21 months. The treatment is a safe and effective alternative to surgery, particularly in cases in which a general anaesthetic is not advisable.