Dilatation of pupils occur in following conditions, except?

SCTIMST Staff Nurse - 2016

Medical & Surgical Nursing

Medium

Appeared in: SCTIMST Staff Nurse - 2016

Explanation

Morphine is a potent opioid analgesic.
Opioid overdose leads to stimulation of the parasympathetic nervous system's control over the pupils.
This stimulation of the Edinger-Westphal nucleus causes the sphincter pupillae muscle to contract, resulting in significant pupillary constriction, often described as 'pinpoint pupils' or miosis.
Because it causes constriction, it is the exception to the other conditions which all cause pupillary dilatation (mydriasis).

Option A: Atropine is an anticholinergic agent that blocks muscarinic receptors, including those on the pupillary sphincter muscle. This blockade prevents parasympathetic-mediated constriction, leading to unopposed sympathetic action and pupil dilatation (mydriasis).
Option C: In brainstem death, the vital centers in the brainstem, including the Edinger-Westphal nucleus (part of the midbrain) which controls pupillary constriction, cease to function. The loss of this parasympathetic tone results in fixed and dilated pupils.
Option D: The third cranial (oculomotor) nerve carries parasympathetic fibers responsible for innervating the pupillary sphincter muscle. A palsy or compression of this nerve interrupts the signal for constriction, leading to an ipsilateral (on the same side) dilated and often non-reactive pupil.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Assessment of pupillary responses in various clinical conditions, including drug overdose and neurological emergencies as background academic context rather than a clinical decision trigger.
Pupillary assessment is a critical, rapid diagnostic tool for nurses in emergency and critical care settings.
The classic triad of opioid overdose is CNS depression (coma), respiratory depression, and miosis (pinpoint pupils). Recognizing this triad is vital for prompt administration of the antidote, naloxone.
A sudden change in pupil size, especially unilateral dilatation, can indicate a neurological emergency like brain herniation and requires immediate escalation to the medical team.

How to Approach the Question

First, identify the keyword 'except'. This signals that you must find the option that is different from the others.
The question asks which condition does NOT cause pupil dilatation. This means you are looking for a condition that causes pupil constriction (miosis) or has no effect.
Recall the autonomic control of the pupil: sympathetic stimulation dilates (mydriasis), and parasympathetic stimulation constricts (miosis).
Evaluate each option: Atropine is an anticholinergic (blocks parasympathetic), causing mydriasis. Brainstem death and CN III palsy involve loss of parasympathetic function, causing mydriasis.
Evaluate the remaining option: Morphine is an opioid known to stimulate parasympathetic pathways, causing miosis.
Conclude that morphine overdose is the correct exception as it causes constriction, while the others cause dilatation.

Concept Tested & Keywords

Concept Tested: Assessment of pupillary responses in various clinical conditions, including drug overdose and neurological emergencies.
Stem keywords: Dilatation of pupils, Atropine overdose, Morphine overdose, Brainstem death, Third cranial nerve palsy
Lead-in keywords: except
Negative lead-in flag: The question uses the word 'except', requiring identification of the option that does not fit with the others.

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E6 Medicine Harrison 22e Part 1 pp. 231-233, 262-264