Some people have a difference in pupil size from birth, particularly if forceps were used during delivery. This difference in pupil size is not linked with any underlying condition. This difference is the same, regardless of whether they are in a dark room or in bright light. Many people have a difference of up to 1mm between the two pupils.

The pupil also becomes smaller when we focus on something close-up, thereby helping the eye to focus an image onto the back of the eye. In bright light, the pupils become smaller so the light doesn’t dazzle us. In a dark room, the pupils become bigger to let more light in, so we can still see. By changing the pupil size, light more or less enters the eye. The iris is a ring-shaped muscle - more precisely, it contains two muscles, one to make the pupil bigger, and the other to make the pupil smaller. The pupil is the ‘hole’ in the centre of the iris, the blue/brown part at the front of the eye. Is this something to be concerned about if you notice it in your child?ĭr Annegret Dahlmann-Noor, director of the children’s eye service at Moorfields Eye Hospital, London, discusses this issue in this informative article for parents and carers.

However, it’s possible that they are different sizes. Any prescribed treatment will likely aim to address the underlying cause of your anisocoria.It goes without saying that our pupils are an incredibly useful part of our eyes because of how they automatically adjust to light, allowing us to adapt to our environment in an instant. 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. If you notice a sudden difference in size between your pupils, you should contact your eye doctor immediately. What do I do if I notice that I have unequal pupils? 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. In this type of anisocoria, the unequal pupil sizes occur as a side effect of medication. 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. Damage to the eye can include eye trauma, complications after or resulting from eye surgery, glaucoma or inflammation of the eye.Ĭongenital anomalies (anomalies present from birth) present in the iris are also classified under mechanical anisocoria. When unequal pupil sizes are caused by damage to the eye, it falls under the category of mechanical anisocoria. This constriction then results in anisocoria.

For example, in people with Horner’s syndrome, one of the symptoms is miosis, which is the constriction of one pupil. Pathologic anisocoria is unequal pupils caused by an underlying condition or disease, such as Horner’s syndrome or Third nerve palsy. In fact, simple anisocoria can be intermittent or constant, and may sometimes even go away on its own without any medical intervention.

Simple anisocoria is the most common type, and is generally not a cause for concern. 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. There are four different types of anisocoria, and each type has different causes and manifestations: 1. 4 different types of anisocoria ( unequal pupils ) and their causes One pupil may be larger than normal, or one pupil may be smaller than normal, therefore resulting in unequal pupil sizes. In most people, they are usually the same size in both eyes.įor people with anisocoria, the pupil sizes in both eyes are different. Pupils, the black circles at the centre of our eyes, are what allows light to enter our eyes so that we can see. If you have unequal pupils, you could be suffering from anisocoria.

One pupil bigger than the other