The Functional and Histopathologic Change in the Levator Palpebrae Superioris and Muller Muscle After Subconjunctival Injection of Triamcinolone Acetonide

Abstract

Aims: The aim of this study was to evaluate the functional and histopathologic changes in the levator palpebrae superioris and Muller muscles after subconjunctival injection of triamcinolone acetonide (TA) in rabbits. Methods: Twenty-four white New Zealand rabbits were divided into 2 groups. In group A, a subconjunctival injection of 0.5 mL TA (40 mg/mL) was administered to the right eye, whereas a normal saline injection of the same volume was administered to the left eye. In group B, the same procedures were done with a 1.0-mL injection of TA or normal saline into each eyelid. Follow-up was done to evaluate the histopathologic changes in the levator and Muller muscle, and changes in the mean transectional area of Muller muscle, and changes in upper-lid height (marginal reflex distance 1) at 1, 2, 4, and 6 weeks after injection. Western blot analyses were used to determine the levels of myosin light chain phosphorylation and alpha-smooth muscle actin, which are related to the contractility of Mull music Results: No specific changes in marginal reflex distance 1 were noted in either group A or B. No significant histopathologic changes were found in the levator muscles. However, significant thinning of Muller muscle were found, and myosin light chain phosphorylation and alpha-smooth muscle actin levels were decreased. This was consistent with the histologic changes of Muller muscle observed in rabbits that received a TA injection. These changes were reversible and influenced by the volume of the injection. Conclusions: Subconjunctival injection of TA into the upper eyelids appears to be temporally influential on both the functional and histopathologic changes of Muller muscle in rabbi. This may be explained by the effect of improvement in lid retraction regardless of the minimal specific change observed in the levator muscle.