Action of Botulinum Toxin on Isometric Contraction of Medial and Lateral Rectus Muscles in Esotropic or Exotropic Patients

Purpose: To study the action of botulinum toxin A on isometric contraction of the medial and lateral rectus muscles in esotropic or exotropic patients. Methods: Isometric contraction in patients with strabismus (exotropic and esotropic) and in volunteers without strabismus was compared 30 days after the use of botulinum toxin A. Results: Findings show that this drug has changed the strength ratio between direct agonist and antagonist muscles. This has promoted the displacement of the point of equilibrium between muscle strengths toward the nasal direction in esotropic cases, toward the temporal direction in exotropic cases, and subsequent deviation of the eye toward its primary position. The average achieved correction was approximately 10 prism diopters in both groups of patients. Conclusion: In both exotropia and esotropia, the average variations in the induced points of equilibrium related to injection of botulinum toxin A were similar. This means that the greatest percentage of corrections happened in cases of small deviations.481384