Uneven Pupils

What Causes Uneven Pupils?

Physiological anisocoria is a medical term for uneven pupils. Some people have this medical condition and there may also be no apparent reason for it. In most cases, having uneven pupils isn't anything to worry about. Unless one of the pupils is considerably larger than the other. People who were born with anisocoria are known to have a deformity of the nerve pathways that control the pupil.

To properly diagnose why a person is suffering with uneven pupils, it all depends on which eye is affected and which one of the pupils is either smaller or larger than the other. For example, if one of the pupils is smaller and does not react to the dimming of light, there may be a defect in the sympathetic fibers. This is called Horner's syndrome. But if there are no deformities to the eye, there are several other reasons why a person can suffer with uneven pupils.

If a person receives a blow to the head they might end up with uneven pupils. Even if the injury does not seem to be severe, if there is any bleeding inside the skull it can result in anisocoria. A brain tumor or abscess inside of the skull can also cause uneven pupils but this isn't because of blood loss. It is a result of pressure on the back of the eye causing the nerves to react.

Meningitis is an infection of the membranes that surround the brain. It can also have an affect on the pupils. In this case, uneven pupils are a symptom of this particular disease. People who suffer with meningitis are usually given antibiotic therapy to control all of the symptoms of the infection and the uneven pupils usually go away.

Oculomotor nerve palsy affects the ocular mobility. One pupil may appear larger than the other and poorly reacts to light. This type of problem usually stems from a lesion that is putting pressure on the eye. This condition is called Hutchinson pupil.

Tonic pupil syndrome is another condition that affects the pupils. It is most common in younger women and always starts in one eye. This condition is not considered dangerous and is not a symptom of any other disease. But people who have tonic pupil syndrome do have problems focusing because of diminished tendon reflexes.

Certain types of eye drops can make uneven pupils. People who wear contact lenses and have other allergies associated with the eye use different types of eye drops. Some of these affect the eye by dilating the pupils or changing ocular mobility. This isn't considered dangerous but can be a cause of concern if the condition has never presented itself before.

A third cranial nerve abnormality can not only affect pupil size but also affects the eye movement and eyelid position. There is usually only one eye that has a different sized pupil but the eye lid itself, over the dilated eye can become droopy. This is a clear indication of third cranial nerve malfunction. The eye will not move properly and if the problem stems from a third cranial nerve palsy it can be life threatening and should be treated immediately.


When it comes to treating anisocoria, it is different for every individual case. If the uneven pupils are a result of using the wrong eye drops, the doctor can prescribe new ones. But if the uneven pupils are a symptom of another disease, than surgery will probably be needed to correct the problem.

If you notice a change in your pupils it is a good idea to see a doctor. Most of the time the condition can be cleared up easily. But in some cases the reasons behind anisocoria can be life threatening.