The ciliary muscle is a ring of smooth muscle within the ciliary body that controls the shape of the crystalline lens for accommodation. When the ciliary muscle contracts in response to parasympathetic stimulation during near vision, the ciliary ring constricts, the zonular fibres relax, and the elastic lens springs to a more convex shape to increase its refractive power. Relaxation of the ciliary muscle, under sympathetic influence, allows the zonules to tighten and flatten the lens for distance vision.
| Origin | Scleral spur and trabecular meshwork at the anterior chamber angle |
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| Insertion | Ciliary processes and the choroid posteriorly via the ciliary crown |
| Nerve Supply | Parasympathetic fibres from the ciliary ganglion via the short ciliary nerves (CN III pathway) |
| Blood Supply | Major arterial circle of the iris |
| Actions | Contraction relaxes the zonular fibres, allowing the crystalline lens to become more convex (accommodation for near vision); Longitudinal fibres open the trabecular meshwork, facilitating aqueous humour outflow |
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Presbyopia is the gradual loss of accommodation due to hardening of the crystalline lens and reduction in ciliary muscle effectiveness with age, beginning at approximately 40 years. Cycloplegic agents (cyclopentolate, atropine) paralyse the ciliary muscle, preventing accommodation, used to accurately measure refractive error in children and to treat inflammatory uveitis by preventing ciliary spasm. Pilocarpine contracts the ciliary muscle and the sphincter pupillae and also opens the trabecular meshwork, lowering intraocular pressure in glaucoma.
Not palpable; assessed indirectly by accommodation testing and slit-lamp examination.
Sustained involuntary contraction of the ciliary muscle in young patients (often from prolonged near work or emotional stress) produces pseudomyopia with blurred distance vision, headache, and eye ache, managed with cycloplegic drops and vision therapy.
Age-related stiffening of the crystalline lens reduces its ability to change shape in response to ciliary muscle contraction, producing the gradual loss of near vision accommodation after age 40 that is corrected with reading glasses, bifocals, or contact lenses.
