Binocular diplopia in unilateral aphakia: the role of botulinum toxin.

We have treated 12 unilaterally aphakic patients, with a manifest squint and binocular diplopia, with botulinum toxin injection to the appropriate horizontal rectus muscle, in an attempt to reduce the angle of squint and thereby resolve the diplopia. In all cases a short-term reduction in the angle of squint was achieved. In nine patients, whose aphakia was corrected with a contact lens, and eight of whom had had their lenses removed because of trauma, this reduction was only temporary. In three patients, however, who had had a non-traumatic cataract removed, replaced with a posterior chamber implant, control of the deviation was maintained long after the acute effect of the toxin had disappeared, with the development of coarse binocular single vision, a fusion range, and abolition of all diplopia. The possible reasons for these different responses are discussed and it is suggested that in cases of binocular diplopia following lens extraction, botulinum toxin treatment should be considered prior to any extraocular muscle surgery, as temporary reduction of the deviation may be sufficient to allow recovery of binocular single vision.