Unequal Pupil Size - Causes, Symptoms, Diagnosis, and Management

The pupil is the black-colored opening in the center of the eye. It allows light to the cornea and adjusts its size according to the amount of light. Ideally, no two pupils can be of the same length or diameter. However, if the difference in the diameter exceeds 1 mm, it may be termed anisocoria (unequal pupil size). This condition is quite common, and it is said that 15 % of the population would have experienced it at some point in their lives. Anisocoria can be congenital. It can be present since birth, or it may have occurred suddenly due to some underlying disease. However, if it appears suddenly, it may be a cause of concern.

What Are the Symptoms of Unequal Pupil Size?

Symptoms may accompany varying pupil sizes or be pointed out by someone else. A medical practitioner may also diagnose it during a regular visit. Anisocoria may be associated with ocular as well as non-ocular symptoms.

Ocular Symptoms May Include:

1. One pupil that is bigger or smaller in size.

2. Pain in the eyes.

3. Vision loss.

4. The blurring of the vision.

5. Double vision or diplopia.

6. Photophobia or sensitivity to light.

7. Redness of the eye.

Non-ocular Symptoms May Include :

1. Fever.

2. Headache.

3. Nausea.

4. Vomiting.

5. Neck pain.

6. Stiffness in the neck.

7. Dizziness.

What Are the Causes of Unequal Pupil Size?

Causes That May Not Be Associated With Underlying Pathology:

1. Drugs: Consumption of certain drugs may cause the pupil to become bigger or smaller. Drugs that may have an effect on the pupil include Anticholinergics, Pilocarpine, and Sympathomimetics.

2. Consumption of Cocaine: Cocaine can cause the pupils to become bigger.

3. Injury: Injury or trauma to the head, eye, or neck can lead to conditions that may cause the alteration of pupil size. During an injury to the eye, a total or partial separation of the iris may be seen.

Causes That May Be Associated With Underlying Pathology:

1. Migraine: Migraine is a neurological condition that is associated with unilateral headaches. Under such conditions, a person may have unequal pupil size.

2. Seizures: A person experiencing a seizure attack may present with one pupil bigger or smaller than the other.

3. Glaucoma: It is a condition of the eye in which damage to the optic nerve can occur. This condition, at times, can cause one pupil to be bigger than the other.

4. Third Nerve Palsy: The oculomotor nerve, or the third nerve, serves as the nerve supply to the eye, its muscles, and the pupil. Any damage, tumor, or any other pathology of this nerve can cause the nerve to malfunction, leading to unequal pupil size. Third, nerve palsy can also cause drooping eyelids and the inability of the pupil to contract and relax.

5. Horner's Syndrome: The exact cause of this condition is unknown, but can be caused by a tumor or injury. In this condition, one pupil may be constricted or smaller, leading to unequal pupil size. The constricted pupil may not be responsive to light.

6. Tonic Pupil / Adie Syndrome: Under this condition, one pupil is not responsive to light and remains big. This condition occurs more commonly in women than men in the age group of 20 to 40 years.

Causes That Are Localized to the Brain and Neck:

1. Brain Aneurysms: Brain aneurysms are small bulges in the brain's arteries.

2. Strokes: This damage the brain due to disrupting its blood supply.

3. Brain Tumors: These are tumors of the brain and spinal cord.

4. Meningitis: It is an infection of the brain and the spinal cord.

5. Tumors of the lymph nodes may exert pressure on the nerves.

6. Any injury or block to the vessels of the neck may have an impact on the nerves supplying the eye.

How Are Unequal Pupils Diagnosed?

1. Physical Examination: When one pupil is bigger or smaller than the other, a physical examination is a preliminary investigation that is to be done. A medical practitioner will determine whether the pupil is bigger or smaller. The reaction of the pupil to light will be used as a tool to find this.

2. Other Investigation: The reaction of the pupil coupled with other symptoms will lead to further diagnostic tests such as :

• Blood investigations.
• Computed tomography.
• Magnetic resonance imaging.
• Any other investigation as the doctor may deem necessary.

When to Consult a Doctor for Unequal Pupil Size?

Except for congenital cases, wherein one pupil is bigger or smaller than the other, all other cases require immediate medical attention. Unequal pupils can signify some serious underlying medical condition. Hence seeking medical care as a priority is advisable.

How to Treat Unequal Pupil Size?

Treatment of unequal pupil size will be decided based on its causative factor. To treat the condition of the eye, it will be important to address the underlying factors that are causing it. Hence correct diagnosis is the key to the resolution of this condition. Anisocoria that is present since birth requires no treatment as there are no underlying causative factors. In case of anisocoria due to mechanical factors, such as trauma, the injury should be resolved at the earliest. In the case of anisocoria due to any other etiology, it is necessary to address the underlying causes, such as Horner's syndrome and Adie's pupil.

Conclusion:

Anisocoria is a condition that can be resolved by treating the causative factor. Treating unequal pupils is more than just treating irregularities. It is more important to treat the underlying disease, which can be more life-threatening.