It is theorized that brow elevation after treatment with botulinum toxin Type A (BoNT-A) results from inactivation of the brow depressors. Expert consensus is that increased injection depth delivers more BoNT-A to these depressors and causes increased elevation. This technique is applied to the correction of brow height asymmetry.
To compare changes in brow height after deep versus shallow BoNT-A in patients with brow asymmetry.
A prospective split-face analysis was performed on 23 women with eyebrow-height asymmetry. Subjects received 64 units of BoNT-A, divided among 16 injection sites in the glabella, forehead, and lateral canthal area. On the side where increased brow lift was desired, deep injections were performed and shallow injections on the opposite side. Photographs were taken at baseline and Week 4 for comparison measurements.
All 23 women enrolled completed baseline injections and returned for the 4-week follow-up. There was no significant difference at 4 weeks in the change in brow height between the sides that received deep versus shallow BoNT-A injection.
Because of the diffusion of the BoNT-A between muscle layers, the eyebrow depressor muscles cannot be accurately targeted with deep injection into the muscle belly for correction of eyebrow height discrepancies.