Functional and Histologic Changes in the Lacrimal Gland After Botulinum Toxin Injection

Abstract

The purpose of this study was to evaluate changes in tear volume, epidermal growth factor (EGF), and histology of the rabbit lacrimal gland after intraglandular application of botulinum toxin. Ten New Zealand rabbits were separated into 3 groups. Eight rabbits received botulinum toxin injection (2.5 U per 0.1 mL) into the right lacrimal gland and saline injection (0.1 mL) into the left lacrimal gland as a sham control. Two rabbits were untreated to serve as normal controls. Tear volume was measured using cotton thread every 2 weeks, and 4 rabbits were killed after 2 and 4 weeks. The lacrimal glands were surgically excised and sectioned or lysed for gene expression analysis. Epidermal growth factor expression and concentration were evaluated by real-time polymerase chain reaction and enzyme-linked immunosorbent assay; morphometric and histologic analyses were performed. The rabbits that were killed 2 weeks after the injection showed decreased tear volume and increased EGF expression and concentration, but differences were not statistically significant. The rabbits that were killed 4 weeks after the injection exhibited similar results. When all 8 rabbits were considered, we detected a significant decrease in tear volume and increased EGF expression and concentration (P = 0.012, P = 0.011, and P = 0.012, respectively). The EGF level was not significantly correlated with the tear volume. There were no prominent histologic changes between the glands, and the lumen versus fibrosis ratio in the interlobular ducts showed no statistically significant difference. The use of botulinum toxin in patients with epiphora is effective, safe, and repeatable because it reduces tear volume and increases the EGF level to prevent corneal damage while causing no histologic changes.