The functional and histopathologic change in the levator palpebrae superioris and Müller muscle after subconjunctival injection of triamcinolone acetonide

Aims: The aim of this study was to evaluate the functional and histopathologic changes in the levator palpebrae superioris and Müller 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 Müller muscles, changes in the mean transectional area of Müller 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 α-smooth muscle actin, which are related to the contractility of Müller muscle. 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 Müller muscle were found, and myosin light chain phosphorylation and α-smooth muscle actin levels were decreased. This was consistent with the histologic changes of Müller 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 Müller muscle in rabbits. This may be explained by the effect of improvement in lid retraction regardless of the minimal specific change observed in the levator muscle.