title: Decreased tear expression with an abnormal Schirmer's test following botulinum toxin type A for the treatment of lateral canthal rhytides.
abstract: BACKGROUND
  Inactivation of muscles of facial expression by chemodenervation with botulinum toxin remains an off-label indication. Nevertheless, it continues to be a safe and effective technique to improve dynamic rhytides and is the treatment of choice for the hypertrophic lateral fibers of the orbicularis oculi muscle that can cause the superimposed crow's feet.
  
  
  OBJECTIVE
  Although infrequent and self-limiting, the complication of unexpected muscle weakness from toxin diffusion or erroneous placement is documented.
  
  
  METHODS
  However, injection into the pretarsal portion of the orbicularis oculi muscle resulting in unilateral ocular irritation and diminished tear expression as evidenced by a dry eye and an abnormal Schirmer's test has rarely been reported. Direct injection into the pretarsal fibers of the muscle as opposed to diffusion of the toxin into the muscle fibers or the lacrimal gland was consistent with the onset of action of the toxin and the prolonged duration of the ocular symptoms.
  
  
  RESULTS
  Treatment consisted of ocular lubrication until the effects of the toxin dissipated and muscle tone returned. Subsequent treatment did not result in a result in a recurrence of adverse sequelae.
  
  
  CONCLUSIONS
  Facial muscles are small, not isolated, and often have fibers that interdigitate. An important factor in the administration of botulinum toxin is the identification of the muscles responsible for the corresponding rhytide. Precise knowledge of muscular anatomy and function will aid in minimizing this and other potential complications.
authors.affiliation: Department of Dermatology, University of California School of Medicine, San Francisco, California, USA.
authors.forename: Seth L
authors.initials: SL
authors.lastname: Matarasso
mesh_terms: D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000009:adverse effects*; D003937:Diagnosis, Differential; D015352:Dry Eye Syndromes / Q000139:chemically induced / Q000175:diagnosis*; D005152:Facial Muscles / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D009465:Neuromuscular Agents / Q000008:administration & dosage / Q000009:adverse effects*; D015595:Skin Aging
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A