Question

A patient presents with a constricted pupil. Which of the following would most likely be the source of the problem?

1) Inflammation of the iris
2) Damage to the oculomotor nerve
3) Increased sympathetic stimulation
4) Decreased parasympathetic stimulation

Answer 1

A constricted pupil is most likely due to damage to the oculomotor nerve, which carries parasympathetic fibers controlling pupil constriction. Increased sympathetic stimulation or decreased parasympathetic stimulation generally leads to dilation, not constriction.

Step-by-step explanation:

If a patient presents with a constricted pupil, it most likely involves the parasympathetic nervous system, particularly if the constriction is abnormal or paired with other symptoms. The oculomotor nerve (cranial nerve III), which carries parasympathetic fibers, is generally responsible for pupil constriction via the neurotransmitter acetylcholine (ACh). Damage to this nerve or the associated parasympathetic pathway can cause abnormalities in pupil size, such as an unusually constricted pupil (miosis).

Here are the possible reasons for the constricted pupil based on the provided options:

1. Inflammation of the iris could potentially cause a constricted pupil, but it would often be accompanied by other symptoms such as eye pain or redness.
2. Damage to the oculomotor nerve is a more likely source of a constricted pupil, as this nerve controls the muscles that constrict the pupil.
3. Increased sympathetic stimulation typically causes pupil dilation, not constriction, so this is less likely to be the cause.
4. Decreased parasympathetic stimulation could theoretically cause dilation, rather than constriction, of the pupil.