A standard neuro examtests the pupillary reflexes. The pupillary reflexes are involuntary responses of the pupil to light and accommodation. Neurological pupillary reflexes help determine brain health by providing information about essential brain functions like vision and eye movement control and neurological disorders like stroke or brain trauma.
However, some neurologists do not include the pupillary light Reflex in their standard neuro exam. This is because they think pupillary reflexes are unreliable enough to provide meaningful information about brain health.
However, some neurologists feel it is crucial to test all the major reflexes during a physical exam. This article will discuss pupillary reflexes and how they help determine brain health.
What are Neurological Pupillary Reflexes?
Apart from the usual neurological tools doctors use during a physical examination, some vital parameters help assess brain health. These parameters are known as neurological pupillary reflexes, and they include the following:
- Direct Reflex is the first response that occurs when light falls on the eye. It is seen in healthy individuals but may not be present in people with specific brain damage.
- Indirect Reflex: – also known as accommodation reflex- occurs when we look at objects close to us or far away from us (near the point of convergence).
Pupil Reactivity and Its Use for Traumatic Brain Injury Diagnosis and Treatment
Doctors can use the delicate but helpful relationship between the brain and the eyes to assess a brain injury, diagnose it, and provide treatment. The vital role of the pupil in brain health can be seen in the following ways:
A pupil reactivity test is a valuable tool for diagnosing traumatic brain injury (TBI) and other diseases that affect the brain. Therefore, using the neurological pupil index to measure the brain’s health is essential. It can provide doctors with a great deal of information about the patient’s neurological status, and it also helps them determine whether they are suffering from a severe brain injury.
The neurological pupil index (NPi) calculates the degree of reactivity of the patient’s pupils. It is a handy tool in the diagnosis and treatment of brain trauma. This index calculates how much each pupil dilates when exposed to light (the brightness reflex).
The greater the dilation, the more responsive they are to stimulus. Other factors can affect the pupils, such as age and health conditions (e.g., diabetes).
The Abnormal Neurological Pupillary Reflexes
The pupils respond to the brain’s signals and react accordingly through neurological reflexes. These responses are called abnormal neurological pupil reflexes (ANPR). They can be caused by damage to the central nervous system or by some medications. There are many types of ANPR, and here we will cover just a few:
Anisocoria
Anisocoria is a condition in which the pupils are of different sizes. Damage to the optic nerve, trauma or inflammation in the eye, or certain medications can cause it. This condition is often readily diagnosed with an ophthalmoscope, but sometimes it may confuse doctors because other conditions, such as Horner’s syndrome, can also cause it.
Unilateral large pupil
A unilaterally large pupil occurs when one pupil is larger than the other and will not constrict in response to light. Damage to the central nervous system or some medications can cause this condition. Both causes are rare, but they should be considered when diagnosing a large unilateral pupil. A unilaterally large pupil may also indicate a tumor, stroke, or other serious condition.
Unilateral small pupil
This is the opposite of a large unilateral pupil, when one pupil is smaller than the other and does not dilate in response to light. This condition is more common than a large unilateral pupil and can be caused by aging, fatigue, or injury. A small unilateral pupil may also indicate brain trauma or damage to the optic nerve.
Impaired pupillary light Reflex
A pupil that does not react when light is shined into it may indicate a brain tumor or aneurysm. Damage to the optic nerve and retina, which is rare, can also cause it. You can test impaired pupillary light Reflex in the doctor’s office by gleaming a bright light into one eye while blocking the other with a finger or special glasses; usually, both pupils will constrict equally when exposed to the light.
Relative afferent pupillary defect
In this condition, the doctor will shine a bright light into one eye while blocking the other with a finger or special glasses; usually, both pupils will constrict equally when exposed to the light. In relative afferent pupillary defect, however, only one eye’s pupil contracts in response to the light stimulus. The cause is damage to the nerves that take information from the retina back to the brain.
Non-reactive pupil
Sometimes, traumatic brain injuries can cause the pupils to be non-reactive. This means they don’t constrict when exposed to bright light and don’t dilate in response to darkness. Neurologists often use a penlight to test the patient’s pupils, looking for signs of reaction. If the pupils do not respond, this can indicate damage to the nervous system, preventing communication between the eye and brain.
Third cranial nerve palsy
In a patient with a traumatic brain injury, the third cranial nerve can become damaged. This will cause the pupil to be non-reactive. The third cranial nerve controls several functions in the eye, including pupil size and shape. It also controls eye movement and focusing ability. If there is damage to this nerve, it can cause double vision or blurry vision and changes in pupil size and shape (for example, if one pupil is smaller than the other).
Horner’s syndrome
Horner’s syndrome is a condition that causes one side of the face to become pale and have reduced sweating. This is due to damage to the sympathetic nervous system, which controls the body’s blood vessels and sweat glands. When this happens, there may be an imbalance in the amount of blood flowing through these structures on each side of the face—making it appear as though one eye or cheek has become smaller than the other.
Near-light dissociation pupils
In near-light dissociation pupils, the patient has anisocoria (unequal pupils) and a contracted pupil on the side away from the light source, but not when looking at something else. This is because when they look at things with their eyes parallel to each other, one pupil will be larger than the other because of refraction differences between them. However, if they look at something very close, their eyes need to point slightly inward toward each other to focus correctly.
Holmes-Adie pupil (Adie’s tonic pupil)
The Holmes-Adie pupil is a sign of damage to the autonomic nervous system that controls involuntary bodily functions. Here, it affects the parasympathetic nerves that control pupil size and accommodation (the ability of the lens within the eye to focus). When you’re looking at something far away from you, your eyes automatically adjust their shape so they can see clearly.
Argyll Robertson (AR) pupil
Here, the pupil doesn’t react to light and is usually small. This is a sign of damage to the parasympathetic nerves that control pupil size and accommodation (the ability of the lens within the eye to focus). In this case, it affects the parasympathetic nerves that control pupil size and accommodation (the ability of the lens within the eye to focus).
