INTRODUCTION Botulinum toxin type A (BTX-A) has demonstrated impressive safety and efficacy for the treatment of dynamic facial rhytides, particularly in the upper face. Numerous reports have cited an associated brow lift with BTX-A injections in the glabellar complex, presumably caused by deactivation of the brow depressor muscles. Few analyses examining this phenomenon more closely exist, however.
OBJECTIVE The objective was to examine objective changes in eyebrow and eyelid height following BTX-A treatment for glabellar rhytides.
METHODS A retrospective analysis of subjects' photographs taken during a single-center, dose-ranging, parallel-group, double-blind, randomized trial with 1-year follow-up in which women with moderate-to-severe wrinkles at maximum frown received a total of 10, 20, 30, or 40 U BTX-A in seven sites in the glabella alone. Photographs of the eyes and forehead region were taken in repose at baseline and every 2 weeks after treatment for up to 20 weeks. Eyebrow height was measured at midpupillary line (“a”), outer edge (“b”), and medial canthus (“c”). Changes in eyebrow height between baseline and after treatment were recorded for each subject. Brow lift was considered successful if measurements “a” and “b” increased after treatment.
RESULTS A total of 79 women were assessed. Central injections of 20 to 40 U BTX-A into the glabella alone (with the most lateral injection at the midpupillary line) led to an immediate lateral eyebrow elevation, followed by a central and medial eyebrow elevation that peaked at 12 weeks after treatment. The lowest dose of BTX-A (10 U) produced an initial mild brow ptosis and the weakest response.
CONCLUSION Doses of 20 to 40 U BTX-A produced dramatic changes in eyebrow position that may be due to diffusion of BTX-A into and partial inactivation of the medial fibers of the frontalis, with resulting increased muscle tone in the lateral and superior muscle fibers of the frontalis.