In patients presenting with bilateral miosis (i.e. pinpoint pupils) of unknown etiology, the astute clinician may consider acute pontine injury, opiate overdose, or medication-related causes as the source.
In such cases, one should consider performing the simple corneal reflex test to evaluate mid and lower pontine function.
This test consists of lightly touching the cornea with the cotton swab of a Q-tip and observing blink responses in both eyes. It assesses afferent fifth nerve (sensory) and efferent seventh nerve (motor) function.
A normal response is simultaneous (i.e. consensual) eye blinking. An abnormal response may be manifest by midline deviation, followed by relaxation, of the lower eyelids.
TAKE HOME POINT: Corneal reflex testing is an easy way to help distinguish pontine injury from an opiate overdose in patients presenting with pinpoint pupils. Confirmatory studies by way of brain imaging should follow.
