The Role of Calcium Signaling Within the Ciliary Muscle Tissue in the Accommodation Spasm Induced by Carbachol Eye...

Calcium signaling is closely linked to smooth muscle contraction. The ciliary muscle, an intraocular smooth muscle essential for eye focusing, undergoes spasm as the main cause of accommodation spasm. This study aimed to investigate the role of ciliary muscle calcium signaling in this condition.

An accommodation spasm model was established in guinea pigs using carbachol eye drops. Measurements were taken at 7, 14, 21, and 28 days post-administration, including refractive status (retinoscopy), ciliary muscle morphology (light microscopy), calcium concentration (microplate assay), IP3 level (ELISA), and IP₃R/RYR expression (qRT-PCR and western blotting).

In the model eyes, carbachol treatment for 7, 14, 21, and 28 days induced significant myopic refraction, manifesting as accommodation spasm. The ciliary muscle fibers were more densely packed in the model group than in the normal group. Moreover, calcium and IP₃ concentrations were higher in the model group in a treatment duration‑dependent manner, peaking at 28 days. The ratio of IP₃R and RYR protein expression increased in the model group compared to the normal group and was dependent on the duration of medication; IP₃R expression was the highest after 28 days, and RYR expression was the highest after 21 days. The ratio of IP₃R and RYR mRNA expression increased in the model group compared to the normal group; IP₃R expression was higher on the 7^th, 21^st, and 28^th days, and RYR expression was higher on the 28^th day.

The continuous carbachol-induced contraction of the ciliary muscle led to an increase in the concentration of Ca²⁺ in the tissue. Meanwhile, the activation of the intracellular calcium reservoir membrane proteins IP₃R and RYR further led to the release of Ca²⁺. These findings indicate that calcium signaling of the ciliary muscle may contribute to accommodation spasms.