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You could be suffering from anisocoria

What is anisocoria?

Pupils, the black circles at the centre of our eyes, are what allows light to enter our eyes so that we can see. In most people, they are usually the same size in both eyes.
For people with anisocoria, the pupil sizes in both eyes are different. One pupil may be larger than normal, or one pupil may be smaller than normal, therefore resulting in unequal pupil sizes.

4 different types of anisocoria and their causes

There are four different types of anisocoria, and each type has different causes and manifestations:

1. Simple anisocoria

Simple anisocoria, also known as essential anisocoria or physiologic anisocoria, is the term for the condition where the difference in pupil size in both the eyes is less than 1 mm, and both pupils react normally when exposed to light. Simple anisocoria is the most common type, and is generally not a cause for concern. In fact, simple anisocoria can be intermittent or constant, and may sometimes even go away on its own without any medical intervention.

2. Pathologic anisocoria

Pathologic anisocoria is unequal pupils caused by an underlying condition or disease, such as Horner’s syndrome or Third nerve palsy. For example, in people with Horner’s syndrome, one of the symptoms is miosis, which is the constriction of one pupil. This constriction then results in anisocoria.

3. Mechanical anisocoria

When unequal pupil sizes are caused by damage to the eye, it falls under the category of mechanical anisocoria. Damage to the eye can include eye trauma, complications after or resulting from eye surgery, glaucoma or inflammation of the eye.

Congenital anomalies (anomalies present from birth) present in the iris are also classified under mechanical anisocoria. Some examples of this condition include coloboma, which is a gap in the iris that gives the pupil a distinct cat-eye appearance, or aniridia, which is an eye condition where there is a complete or partial absence of the iris of one eye.

4. Pharmacologic anisocoria

In this type of anisocoria, the unequal pupil sizes occur as a side effect of medication. Certain drugs have been identified that could be potential causes of pharmacologic anisocoria, such as anti-depression medication, chemotherapy, patches used to treat motion sickness, or certain glaucoma eye drops.

What do I do if I notice that my pupils have become unequal?
If you notice a sudden difference in size between your pupils, you should contact your eye doctor immediately. Depending on your symptoms and medical history, your eye doctor might conduct tests, such as eye exams and blood work, to help diagnose the underlying cause of your anisocoria. Any prescribed treatment will likely aim to address the underlying cause of your anisocoria.