Botulinum toxin injection into Riolan's muscle: somatosensory 'trick'.

We studied the effect of injecting botulinum toxin A (BTX-A) into the pars ciliaris--also known as Riolan's muscle--of patients with eyelid apraxia (ELA). Six patients with ELA were treated with injections of BTX-A into the region of Riolan's muscle at the medial and lateral portions of the upper and lower pretarsal orbicularis oculi. Clinical benefit was seen in all 6 patients, 2 of whom had previously been treated with conventional pretarsal injections of BTX-A and had not improved. BTX-A injections into Riolan's muscle are effective as treatment for ELA. The proposed mechanism is not that of muscle relaxation but rather modulation of the somatosensory cortex, similar to that of a 'sensory trick' in patients with dystonia.