The brow lift is a surgical procedure that has been practiced for several decades. A typical indication is brow ptosis, which can be secondary to involutional changes or facial nerve palsies. Several techniques have been described, including direct, mid-forehead, coronal, and endoscopic approaches. Of these options, the direct brow lift allows for predictable post-operative brow contour and excellent control over the degree of lift achieved. As with any surgical procedure, with direct brow lift comes known undesirable post-operative outcomes, the most common of which is forehead paresthesia from supraorbital nerve damage. Other complications include alopecia and brow asymmetry. However, one of the main critiques of direct brow lift remains the poor cosmesis that can result from scarring just above the brow. A study conducted by Cho et al. concluded that of the main surgical techniques currently employed for treatment of brow ptosis, direct brow lifts held the highest rates of visible scarring.

Scarring can significantly impair an individuals' quality of life. This is particularly true of facial scarring, which is often difficult to conceal. Much research has been conducted in the area of treating postoperative, traumatic, and burn-related scarring. Cadet et al completed a randomized controlled trial using topical silicone gel for direct brow lift-related scarring, given the known benefit of silicone gel sheeting for the same, but did not find a significant difference between treatment and control groups. Some effective techniques described in the literature to date include long-pulsed non-ablative Nd:YAG laser, as well as intralesional steroid injection. On the rise are studies looking into the use of botulinum toxin A for treatment of unfavourable scarring and improved facial cosmesis.

Botulinum toxin is a neuromodulatory agent that has garnered usage in a variety of therapeutic and cosmetic settings. More recently, injection of botulinum toxin as a means to reduce scarring and improve outcomes in wound healing has been investigated. Several studies, including two large metaanalyses, have shown this to be an effective method of treatment. Proposed mechanisms include increased apoptosis and suppressed proliferation of fibroblasts treated with botulinum toxin, modulated via the PTEN/PI3K/Akt pathway. Park et al added to the in vitro literature by demonstrating that fibroblasts treated with botulinum toxin A produced fewer extracellular matrix proteins and pro-fibrotic factors compared to untreated cells. Another underlying mechanism that results in suboptimal wound healing is the constant contraction and relaxation of facial muscles, causing repetitive microtrauma that ultimately increases inflammation and impairs wound healing. It therefore stands to reason that by temporarily paralyzing local musculature during the post-operative period, collagen maturation can take place uninterrupted by excessive tensile forces.

Despite scarring being a widely known and undesirable complication of direct brow lift surgery, there have been no studies to date examining the use of onabotulinum toxin injection to reduce said scarring and improve outcomes. With this double masked, prospective, randomized controlled trial, the investigators aim to determine whether injection of onabotulinum toxin immediately following direct brow lift surgery can improve scores on validated patient and observer scar scales.

The patient population to be studied will include patients undergoing bilateral direct brow lifts at the Victoria General Hospital in Halifax, Nova Scotia.

Patients must meet all of the following inclusion criteria, and have none of the exclusion criteria listed below.

Inclusion criteria:

• Participants must be over 18 years of age
• Participants must be able to attend outpatient appointments at the Victoria General Hospital
• Participants must be able to give informed consent

Exclusion criteria:

• Known allergy to botulinum toxin
• Previous scarring in same region of surgical procedure
• Previous botulinum toxin injection within 6 months of surgical date for direct brow lift
• Currently pregnant or breast feeding
• History of keloid or hypertrophic scarring
• History of myasthenia gravis/ neuromotor disorder

Computer randomization software will be used to determine whether the right or left side will receive onabotulinum toxin injection. The contralateral side will receive a placebo injection of equal volume (normal saline).

The health care professional assisting with the procedure will not be masked to randomization. He/she will draw up the onabotulinum toxin A and placebo in two separate identical syringes marked A (right side) and B (left side). They will reference a form showing the results of the computer generated randomization, which will be kept in a study chart separate from the patient's normal oculoplastic visits. They will sign this form, as well as record the lot number of the onabotulinum toxin A and normal saline.

The oculoplastic surgeon will visually divide each incision in half, and inject half of the volume of syringe A at each side of the right direct brow lift incision, and half of the volume of syringe B at each side of the left direct brow lift incision.