What is the pupillary reflex?

From the Guidelines

The pupil reflex is a critical component of a neurological examination, and its assessment is essential for evaluating the integrity of the autonomic nervous system and brain function, as highlighted in the 2023 study on pediatric eye evaluations preferred practice pattern 1. When assessing the pupil reflex, clinicians should evaluate the size, shape, symmetry, and response to light, as well as the presence of a relative afferent pupillary defect, which can indicate a unilateral problem with the optic nerve or other areas in the anterior visual pathway 1. The swinging-light test is a useful method for assessing the pupillary reflex, where a penlight is shined in one eye and then quickly moved to the other eye, observing for pupillary constriction or dilation, which can help identify an afferent pupillary defect 1. Abnormal pupillary responses can indicate various conditions, including brain injury, nerve damage, or drug effects, and the speed, symmetry, and completeness of pupillary reactions provide valuable diagnostic information about the integrity of neural pathways and brain function 1. In clinical practice, the assessment of the pupil reflex should be performed in a systematic and thorough manner, taking into account the patient's age, medical history, and any potential underlying conditions that may affect the pupillary response, as emphasized in the 2020 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1. Key considerations in the assessment of the pupil reflex include the use of a bright light source, the observation of both direct and consensual responses, and the evaluation of the pupillary response in both eyes, as outlined in the 2011 clinical report on guidelines for the determination of brain death in infants and children 1. By prioritizing the assessment of the pupil reflex and using a systematic and thorough approach, clinicians can gather valuable information about the patient's neurological function and make informed decisions about their care. Some important points to consider when assessing the pupil reflex include:

• The size and shape of the pupils should be evaluated in dim light to assess for any differences in size, which can be clinically significant if greater than 1 millimeter 1.
• The pupillary response to light should be evaluated by shining a light directly into each eye and observing for constriction or dilation, which can help identify an afferent pupillary defect 1.
• The swinging-light test should be performed to assess for the presence of a relative afferent pupillary defect, which can indicate a unilateral problem with the optic nerve or other areas in the anterior visual pathway 1.
• The assessment of the pupil reflex should be performed in a systematic and thorough manner, taking into account the patient's age, medical history, and any potential underlying conditions that may affect the pupillary response 1.

From the FDA Drug Label

CLINICAL PHARMACOLOGY This anticholinergic preparation blocks the responses of the sphincter muscle of the iris and the accommodative muscle of the ciliary body to cholinergic stimulation, producing pupillary dilation (mydriasis) and paralysis of accommodation (cycloplegia). CLINICAL PHARMACOLOGY This anticholinergic preparation blocks the responses of the sphincter muscle of the iris and the ciliary muscle to cholinergic stimulation, dilating the pupil (mydriasis).

The pupil reflex is affected by both cyclopentolate and tropicamide, as they both cause mydriasis (pupillary dilation) by blocking the responses of the sphincter muscle of the iris to cholinergic stimulation.

• Cyclopentolate produces mydriasis and cycloplegia (paralysis of accommodation) 2.
• Tropicamide also produces mydriasis, and the stronger preparation (1%) paralyzes accommodation 3.

From the Research

Pupil Reflex Overview

• The pupil reflex, also known as the pupillary light reflex, is a critical component of the neurological examination 4.
• It involves the constriction and dilation of the pupils in response to light and is controlled by the autonomic nervous system.

Abnormal Pupil Reflex

• Abnormalities in the pupil reflex can indicate various neurological conditions, such as Horner syndrome 5 or Holmes-Adie syndrome 6.
• In Horner syndrome, the pupil reflex is affected due to disruption of the sympathetic nerves supplying the eye, resulting in miosis (pupil constriction) and ptosis (eyelid drooping) 5.

Diagnostic Techniques

• Pupillometry is a diagnostic technique used to assess the pupil reflex and has been shown to be more accurate than manual penlight examination in neurocritical care populations 7.
• Automated pupillometry can detect early changes in neurologic function, intracranial pressure, and treatment response to osmotherapy, making it a valuable tool in neurocritical care 7.

Prognostic Value

• The absence of the pupillary light reflex 3 days after cardiac arrest has been shown to predict poor outcome 8.
• Quantitative assessment of the pupillary light reflex using pupillometry has been found to predict poor outcome early after cardiac arrest, with nonreactive pupils being associated with high mortality 8.

Clinical Applications

• Pupillometry has been used to identify patients with disturbed irideal innervation, such as those with Horner syndrome or Holmes-Adie syndrome 6.
• Dilute solutions of phenylephrine and pilocarpine can be used to diagnose disordered autonomic innervation of the iris, with supersensitivity to these agents being a useful diagnostic feature 6.