What Is the Cause of Abnormal Pupillary Responses?

The pupils have what medical professionals consider being a normal response to light and other stimuli. These responses are necessary for the body to function properly and are essential to the neurological system.

When a patient has abnormal pupillary responses, the pupils are not responding correctly. This may indicate an underlying traumatic brain injury that requires treatment.

This article describes abnormal pupillary responses and how they relate to TBIs.

What is an abnormal pupillary response?

An abnormal pupillary response is the inability of the pupils to respond normally. Traumatic brain injuries (TBIs) or other health problems can cause it, but it is infrequent in patients without a history of head trauma.

The pupils respond to light, so if they do not respond properly, this can indicate an underlying problem.

Examination of pupil reactivity

There are different ways in which a doctor can examine pupil reactivity. Some of them include:

• General pupil evaluation: The doctor will examine pupils’ size, shape, and reactivity. While performing the pupillary evaluation, they should check for any asymmetry between them.
• Pupillary observation: Doctors should perform a pupil diameter measurement to know if the pupils react together to light. If there is any difference in the pupils’ response, it could be a sign of neurological or other health problems.

Pupillary reflex tests

As an additional way to check pupil reactivity, doctors can conduct different pupillary reflex tests. They include:

• Light reflex: This is the most common pupillary reflex test. Here, doctors shine a light in one eye of the patient and then observe how their pupils react to it. If the pupil constricts when exposed to light, this is a good sign that everything is fine with that eye. They will repeat the same test with the other eye. The light reflex should be equal in both eyes. If there is a difference, it could be a sign of problems with that eye and the brainstem.
• Swinging flashlight test: This test is like the light reflex test but requires a swinging flashlight instead of a steady one. Doctors will hold up the flashlight and ask patients to follow it with their eyes as they move it back and forth. If the pupil constricts when exposed to light, this is a good sign that everything is fine with that eye. They will repeat the same test with the other eye.
• Near reflex test: This involves pupil measurement. The doctor will have a patient look at a small object that is held close to the eye. If they can focus on it, this is a good sign that there are no problems with their vision and brain.

Abnormal pupillary responses

We will now look at some of the abnormal responses that can be seen in the pupillary reflex test.

1. Anisocoria

This is when one pupil is bigger than the other. Damage to the sympathetic nerve fibers, which connect the brainstem to each eye, can cause this. A mild anisocoria will not affect the patient’s ability to see properly, but it could indicate a more severe problem.

2. Unilateral large pupil

This is when a pupil is larger than the other in a dark room. Damage to the parasympathetic nerve fibers, which connect the brainstem to each eye, can cause it. This could mean a problem with the cranial nerves that control eye movement and muscle function.

3. Unilateral small pupil

Here, the pupils do not dilate when exposed to light. This could be due to damage to the sympathetic nerve fibers, which connect the brainstem to each eye. It may also indicate damage to the oculomotor nerve, which controls eye movement.

This condition leads to asymmetric photophobia and asymmetric pupil dilation.

4. Non-reactive pupil

When the pupils are non-reactive, there is no change in size when exposed to light. We can divide this condition into two:

• Unilateral non-reactive pupil: This is a condition in which the pupil does not react to light on one side of the eye. It may be due to damage in the oculomotor nerve pathway, which controls eye movement.
• Bilateral non-reactive pupils: This is a condition in which both pupils are not reactive to light. This can happen when the retina, optic nerve, or brain is damaged.

Conclusion:

Abnormal pupillary reactions are a common condition caused by various illnesses and injuries. Pupils can be reactive or non-reactive to light; a doctor must perform a pupillary evaluation to ascertain these conditions.