The circularly arranged smooth muscle fibers in the highlighted structure perform which function?

Answer:constriction of pupil

Explanation:the circularly arranged smooth muscle fibers in the highlighted structure ie the iris causes constriction of the pupil.

The iris basically has ciliary muscles that control Lens shape, this happens when the ciliary muscles under the signal of the parasympathetic nervous system contract leading to the constriction of the pupil and when these muscles relax then dilation of the pupil will occur