[The dose-response relationship in treatment of strabismus with botulinum toxin]

The dose-response relationship between botulinum toxin and the alteration of ocular alignment of 15 esotropia cases (ET) and 15 exotropia cases (XT) was evaluated. We began with a dose of 0.25 units (U) per injection and stepped it up to 2.5 U per injection in ET and to 10 U per injection in XT. The average number of injections was 3.6 and 5.2, respectively. The maximum effect on ocular alignment developed 7 to 14 days after injection, and following recurrences ceased within 2 to 6 months, indicating a lasting effect. The maximum effect of each injection was within the limits of 10 to 30 prism diopters (delta). The maximum effect per unit dose of the small dose injection was greater than that of the large dose injection. In each dose, a greater effect was observed in the ET than in the XT, Recurrence was within the limits of 8 to 21 delta with both small dose injection and large dose injection. The recurrence amount per unit dose was greater with small dose injection than with large dose injection. The larger the dose injected, the more lasting was the effect obtained. This tendency was more prominent in ET than in XT. A roughly linear relationship between the dose and the ocular alignment was obtained on logarithmic graph paper, and the recurrence was reduced when the dose was increased. These findings suggest that repetitive injection effectively accumulates, resulting in a lasting effect.