Lacrimal Gland Botulinum Toxin Injection Versus Simple Glandular Needling: Histopathological and Electron Microscopic Evidence and Potential Clinical Implications.

Abstract

To investigate the histopathological and ultrastructural changes in the lacrimal glands (LGs) of rabbits following either botulinum toxin (BTX) injection or simple glandular needling. Twenty-four LGs of 24 eyes of 12 healthy New Zealand white rabbits were included in the study. Of these, 4 LGs of 4 eyes of 2 rabbits were used as controls. In the intervention group, all the right LG received 5 U in 0.1 ml of BTX-A (Botox, Allergan, Dublin, Ireland) and the left LG received simple glandular needling under general anesthesia. The BTX-A was injected directly into the LG via the transconjunctival route under direct visualization. For simple needling, 5 LG passes were made through a single-entry point using a 29-gauge needle mounted on an empty tuberculin syringe. The rabbits did not receive any postoperative medications other than lubricants. The rabbits were sacrificed at 8 weeks and the 20 treated and 4 control LG's were retrieved for histopathological and transmission electron microscopic (TEM) analysis as per standard protocols. In comparison to the control LG samples, both the treated groups showed pathological changes, which were more pronounced in the simple needling group. The BTX-A-treated LGs showed mild to moderate acinar atrophy, few degenerating acini and patchy chronic inflammatory infiltrates with thick hyalinized collagen within the glandular stroma. TEM analysis showed the cytosol of few acinar cells to contain vacuoles and autophagosomes with marginal chromatin condensation of the nucleus and an eccentric nucleolus. The LGs treated with simple needling showed marked pathological changes which include moderate to severe, focal, and diffuse acinar atrophy, dense stromal fibrosis, inflammatory infiltrates, and peri-vasculitis. TEM analysis showed focal disorganized acinar morphology, loss of intra-acinar and ductal architecture, and needle track zones with surrounding fibrotic areas. Histopathological and ultrastructural changes were noted in the LGs treated with BTX-A and simple glandular needling. Simple needling of the LG has the prospect to be an effective and cheaper alternative to BTX-A.