Patient Experience

  • Reference Number: HEY1420-2023
  • Departments: Ophthalmology Department
  • Last Updated: 1 November 2023


This leaflet has been produced to give you general information. Most of your questions should be answered by this leaflet. It is not intended to replace the discussion between you and the healthcare team, but may act as a starting point for discussion. If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team.

What is anisocoria?

Anisocoria is the medical term for unequal pupil sizes. The pupil is the black centre of the eye that controls how much light enters the eye. Anisocoria is a relatively common condition, affecting about 20% of the population. It can be present from birth or develop later in life.

What causes anisocoria?

There are many different causes of anisocoria, including:

  • Physiological anisocoria: This is a normal variation in pupil size that is present from birth. It is usually very slight and does not cause any vision problems.
  • Drug related anisocoria: There are many medications or chemicals that can cause the pupil to dilate or constrict. While some of these medications are intentionally used in the eye, sometimes these medications or chemicals are accidentally rubbed into the eye from your skin, usually by your finger. Eye drops that dilate or constrict the pupil. Other chemicals that affect the pupils: pesticides, the ingredients on flea collars, skin patches for motion sickness, inhalers for asthma, antiperspirant wipes.
  • Pathological anisocoria: This is caused by a medical condition, such as a previous viral infection, compressing lesion, stroke, or injury to the nerve that control the pupil size.
  • Intermittent anisocoria: This is a temporary rather than persistent type of pupil asymmetry, when one pupil dilates for a limited period of time before returning back to the normal size, the condition is called “springing pupil”, the exact cause of this phenomenon is not known but is thought be migraine related.

What are the symptoms of anisocoria?

Most people with anisocoria do not have any symptoms. However, in some cases, anisocoria can be associated with vision problems, such as blurred vision, double vision, or difficulty seeing in certain light conditions. Anisocoria may also be a sign of a serious medical condition.

How is anisocoria diagnosed?

Anisocoria is usually diagnosed during a routine eye exam. The eye doctor will look at the pupils in both a lighted room and a dark room to see how they respond to light. They may also ask about your medical history and perform other tests, such as instilling eye drops, taking photographs, performing a visual field test or a neurological exam.

How is anisocoria treated?

The treatment for anisocoria depends on the underlying cause.  If the anisocoria is caused by a medical condition, that condition will need to be treated.  If the anisocoria is caused by eye drops or medications, those medications may need to be changed.  In some cases, there may be no need for treatment.

A pupil that is chemically dilated or constricted will return to normal size and function, as the chemical wears off. Depending on the specific chemical, this can take hours or days.

What are the complications of anisocoria?

The complications of anisocoria depend on the underlying cause.  If the anisocoria is caused by a serious medical condition, it can lead to certain health problems. However, in most cases, anisocoria is not a serious condition and does not cause any complications.

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the ophthalmology department on tel: 01482 608788

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats you, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to you. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your condition, the alternatives available to you, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

Information about you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide you with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your doctor, or the person caring for you.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.