High versus low concentration botulinum toxin A for benign essential blepharospasm: does dilution make a difference?

To evaluate the efficacy and side effects of concentrated versus dilute botulinum toxin A in treating benign essential blepharospasm.

The authors performed a prospective randomized clinical trial of 16 patients with an established diagnosis of benign essential blepharospasm. Patients were randomized to receive low concentration (control, 10 U/ml) injections on one side and high concentration (experimental, 100 U/ml) injections on the other. They were surveyed on a scale of 1 to 10 regarding pain, bruising, and redness immediately after the injection. During their return visit, at an established interval of 1 to 3 months, patients were questioned regarding complications (ptosis, diplopia, tearing, and dry eye), duration of relief, and side preferred. Patients were followed over 8 months for 1 to 6 repeat injections, with the side given the higher concentration alternated at each visit.

With 16 patients, there were a total of 42 visits and 84 observations (eyes) documented. Using the Wilcoxon rank sum test, there was a statistically significant reduction in pain scores (1.94 vs. 4.59, p < 0.001) on the experimental side versus the control side. Patient assessment revealed no significant difference in bruising, redness, complications of injection, side preference, or length of relief of symptoms.

Compared with the control, the high concentration botulinum toxin A demonstrated a 58% reduction in perceived pain. Patients did not report a significant difference in efficacy or complications with either dilution.