What is the cause of a non-reactive pupil, also known as a fixed pupil (mydriasis)?

From the Guidelines

A non-reactive pupil is a serious neurological sign that requires immediate medical attention, and the most recent evidence suggests that neuroimaging, including MR imaging with gadolinium and magnetic resonance angiography (MRA) or computed tomography angiography (CTA), should be performed to rule out a compressive lesion, especially an aneurysm involving the posterior communicating artery 1. If you encounter someone with a non-reactive pupil (a pupil that doesn't constrict when exposed to light), you should call emergency services immediately as this may indicate increased intracranial pressure, brain injury, stroke, or other life-threatening conditions. Non-reactive pupils can be unilateral (one side) or bilateral (both eyes), with bilateral fixed pupils generally indicating a more severe condition. This occurs because damage to the brain stem or third cranial nerve disrupts the normal pupillary light reflex pathway. While waiting for emergency services, keep the person still, monitor their breathing and consciousness, and don't give them anything to eat or drink. Some key points to consider in the evaluation of a non-reactive pupil include:

• The presence of associated neurologic symptoms, such as ataxia, tremor, hemiplegia, sixth nerve or fourth nerve palsy, and noted pupillary asymmetry, and vision loss 1
• The importance of a comprehensive eye examination, including a sensorimotor exam, evidence of ptosis and anisocoria, and pupillary responses in bright and dim illumination 1
• The need for neuroimaging, including MRA or CTA, to rule out a compressive lesion, especially an aneurysm involving the posterior communicating artery 1
• The potential for other causes, such as tumors, including meningioma, schwannoma, and metastatic lesions, trauma, subarachnoid hemorrhage, viral illnesses, demyelinating disease, and leptomeningeal disorders 1 Medical professionals will need to perform immediate diagnostic tests like CT scans or MRIs to determine the cause and appropriate treatment, which might include medications to reduce brain swelling (like mannitol or hypertonic saline), surgery to relieve pressure, or other interventions depending on the underlying cause. The prognosis varies widely based on the cause, timing of treatment, and extent of neurological damage. It is also important to note that a non-reactive pupil can be a sign of a serious underlying condition, and prompt medical attention is essential to prevent long-term damage or even death. In some cases, a non-reactive pupil may be a sign of a life-threatening condition, such as a brain aneurysm or stroke, and immediate medical attention is critical to prevent serious complications or death 1. Overall, a non-reactive pupil is a serious neurological sign that requires immediate medical attention, and prompt evaluation and treatment are essential to prevent long-term damage or even death.

From the Research

Non-Reactive Pupil

• A non-reactive pupil can be a symptom of various conditions, including third nerve palsy, which can result from lesions located anywhere from the oculomotor nucleus to the termination of the third nerve in the extraocular muscles within the orbit 2.
• In some cases, a non-reactive pupil may not be present, as seen in a case report of a girl with third cranial nerve syndrome, where there were no changes in pupil reactivity 3.
• The diagnosis and management of third nerve dysfunction vary according to the age of the patient, the characteristics of the third nerve palsy, and the presence of associated symptoms and signs 2.
• Examination of the pupils is a crucial part of any eye examination, and unequal pupils (anisocoria) may indicate underlying disease of the eye, orbit, brain, neck, or chest 4.

Possible Causes

• Third nerve palsy can be caused by various factors, including intracranial aneurysm, pituitary apoplexy, and giant cell arteritis 2.
• Diabetic patients may experience third nerve palsy due to glycemic imbalance and ischemic phenomena caused by cardiovascular risk factors 5.
• Other possible causes of third nerve palsy include trauma, neuro-syphilis, and demyelination secondary to infliximab and multiple sclerosis 6.

Diagnosis and Management

• The management of a third nerve palsy depends on localization of the causative lesion and determination of the underlying etiology 6.
• Recent advances in non-invasive neuroimaging facilitate early diagnosis, and improved imaging technology with high-resolution magnetic resonance imaging (hr-MRI) allows for direct visualization of the entire nerve path and the affected muscles 6.
• Treatment options for third nerve palsy may include strabismus surgery, globe-tethering procedures, and frontalis suspension for correcting ptosis 6.