A dilated right pupil observed during surgery is most likely due to which cause?

A dilated right pupil observed during surgery is most likely due to which cause?

• A. Right stellate ganglion block
• B. Accidental introduction of lidocaine into the right eye
• C. Accidental introduction of phenylephrine into the right eye
• D. Right ciliary ganglion block

Answer: (C)

Pupil size is controlled by a balance between the sympathetic system (which dilates the pupil via the iris radial muscle) and the parasympathetic system (which constricts it via the iris sphincter). Phenylephrine is a direct alpha-1 adrenergic agonist that, when it enters the eye, stimulates the iris dilator muscle to contract, producing rapid, unilateral mydriasis. Intraoperative exposure to phenylephrine is a classic cause of a dilated pupil on the affected side. In contrast, a stellate ganglion block reduces sympathetic tone, leading to miosis (constricted pupil) rather than dilation; a ciliary ganglion block would remove parasympathetic input and cause dilation, but this is less likely to occur accidentally in this setting; and introducing lidocaine into the eye typically causes local anesthesia with less predictable or consistent effects on pupil size.

Pupil size is controlled by a balance between the sympathetic system (which dilates the pupil via the iris radial muscle) and the parasympathetic system (which constricts it via the iris sphincter). Phenylephrine is a direct alpha-1 adrenergic agonist that, when it enters the eye, stimulates the iris dilator muscle to contract, producing rapid, unilateral mydriasis. Intraoperative exposure to phenylephrine is a classic cause of a dilated pupil on the affected side.

In contrast, a stellate ganglion block reduces sympathetic tone, leading to miosis (constricted pupil) rather than dilation; a ciliary ganglion block would remove parasympathetic input and cause dilation, but this is less likely to occur accidentally in this setting; and introducing lidocaine into the eye typically causes local anesthesia with less predictable or consistent effects on pupil size.