Certified Ophthalmic Technician Practice Test 2025 – Complete Exam Prep

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Which mechanism do sympathomimetic agents use to dilate the pupil?

Relaxing the sphincter muscle

Stimulating the ciliary body

Stimulating the radial muscle of the iris

Sympathomimetic agents induce pupil dilation primarily by stimulating the radial muscle of the iris. When these agents are administered, they activate the alpha-adrenergic receptors present in the radial muscle, leading to contraction of this muscle. As the radial muscles contract, the pupil dilates, a process known as mydriasis. This is an important physiological response that occurs independently of the sphincter muscle, which would function to constrict the pupil, and is a different mechanism than directly stimulating ciliary body activity, which primarily affects accommodation and not pupil size. It also does not involve inhibiting parasympathetic activity as a direct mechanism for dilation; rather, it exerts its action through sympathetic pathways promoting dilation.

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Inhibiting parasympathetic activity

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