Complications of botulinum toxin a and their adverse effects

Strabismus. 2009 Oct-Dec;17(4):139-42. doi: 10.3109/09273970903303860.


Aim: To evaluate the prevalence of complications after low doses (< 3 units) of botulinum toxin (BT) injection to horizontal extraocular muscles for diagnostic and therapeutic purposes.

Methods: A case record review was undertaken of patients treated with BT (Dysport) since 2000. Data were extracted for gender, age, diagnosis, number of BT injections, dose, recorded complications, and time to recovery.

Results: Two hundred eleven (211) cases were reviewed, 48.5% children, 51.5% adults (45.5% male, 54.5% female). Diagnoses included constant and intermittent esotropia and exotropia, decompensating esophoria, exophoria and microtropia, accommodative spasm, mechanical restrictions, and cranial nerve palsy. One hundred sixty-three (163) patients had one injection; 38 had two; 7 had three; 2 had four; 1 had six; for a total of 274 injections. BT dose was 1 unit in four cases; 2.5 units in two; 3 units in seven; and 2 units in the remainder. At 2 weeks follow-up, six cases had induced vertical deviation; three had subconjunctival haemorrhage. At 2 weeks, 23 cases had ptosis, but a further 10 cases had ptosis that had resolved by 2 weeks follow-up. All complications had resolved by 6 weeks follow-up.

Conclusions: A low incidence of complications per injection (12.4%) was found particularly for induced vertical deviations (2%) and hemorrhages (1%). Incidence for ptosis was the highest (8.4%). Notably, 10 additional cases of ptosis had resolved before follow-up. Two children were given occlusion therapy to prevent the possibility of stimulus deprivation occlusion until ptosis resolution.

Publication types

  • Comparative Study

MeSH terms

  • Adolescent
  • Adult
  • Blepharoptosis / chemically induced*
  • Blepharoptosis / epidemiology
  • Botulinum Toxins, Type A / administration & dosage
  • Botulinum Toxins, Type A / adverse effects*
  • Child
  • Child, Preschool
  • Eye Movements
  • Female
  • Follow-Up Studies
  • Humans
  • Incidence
  • Injections, Intramuscular
  • Male
  • Neuromuscular Agents / administration & dosage
  • Neuromuscular Agents / adverse effects*
  • Oculomotor Muscles
  • Retrospective Studies
  • Risk Factors
  • Strabismus / drug therapy*
  • Strabismus / physiopathology
  • United Kingdom / epidemiology
  • Young Adult


  • Neuromuscular Agents
  • Botulinum Toxins, Type A