Dose Effect of Botulinum Toxin A in Heterotropia and Heterophoria

Success rates of botulinum toxin in different types of strabismus and dose effect

OBJECTIVE

To determine the effect of botulinum toxin in different types of strabismus and analyze its dose effect.

DESIGN

This was an interventional clinical study performed in a tertiary care university hospital.

METHODS

Eighty six patients treated with botulinum toxin for strabismus were included. Main outcome measures involved success of botulinum toxin, alignment change per unit of toxin, and dose effect on complications and outcomes.

RESULTS

Success rates were 31% for infantile esotropia, 25% for partially accommodative esotropia, 61.5% for residual esotropia, 25% for third cranial nerve paralysis, 13.3% for sixth cranial nerve paralysis, 75% for Duane retraction syndrome, and 38.5% for nonaccomodative esotropia. Improvement in deviation size after botulinum toxin treatment was significant in patients with infantile esotropia (p = 0.001), residual esotropia (p = 0.001), and nonaccomodative esotropia (p = 0.03). Mean deviation change per 1 unit of toxin was 2.7 ± 2.4 prism diopters (PD) with a single injection and 2.1 ± 1.9 PD with multiple injections. A 3.32 PD of early deviation change with botulinum toxin corrected 1 PD of final deviation. Success rate was not correlated with age (r = 0.040, p = 0.8), sex (r = -0.083, p = 0.6), mean dose (r = -0.149, p = 0.35), or total dose (r = 0.165, p = 0.29) but was significantly correlated with deviation size (β = -0.077, p = 0.0001). Complications were not associated with the dose of botulinum toxin (p > 0.05).

CONCLUSIONS

Botulinum toxin has variable outcomes in different types of strabismus. Still, it reduces the deviation size in most patients, thus allowing for a smaller amount of subsequent muscle surgery. Early overcorrection is a more powerfull indicator of better outcome than postinjection duction deficit.

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.