Certified Surgical First Assistant (CSFA) Practice Test

What type of drug can paralyze the sphincter muscle of the iris?

1. Myotics

2. Cycloplegics

3. Anticholinergics

4. Sympathomimetics

The correct answer is: Cycloplegics

The sphincter muscle of the iris is responsible for constricting the pupil, and its paralysis can lead to dilation of the pupil, a condition known as mydriasis. Cycloplegics are drugs that specifically induce paralysis of the ciliary muscle, which is involved in accommodation, but they also have an effect on the iris sphincter muscle. When the iris sphincter muscle is paralyzed, it prevents constriction, consequently leading to dilation. This dilation can be useful during certain ophthalmic procedures where a wider field of view is needed, or to relieve pain associated with certain conditions. Cycloplegics can be administered through topical drops and are often used in both diagnostic and therapeutic settings in ophthalmology. While myotics are drugs that would cause constriction of the pupil, anticholinergics can block the effects of acetylcholine and lead to dilation, but they are more commonly associated with cycloplegic effects rather than directly affecting the sphincter muscle paralysis. Sympathomimetics work by mimicking the effects of adrenaline and can also cause pupil dilation, but they do not directly paralyze the sphincter muscle of the iris in the same way cycloplegics do.