Causes & Concerns Of Dilated Pupils

Causes & Concerns Of Dilated Pupils

Pupils that are larger than normal in size are referred to as ‘dilated pupils’. The size is managed by muscles located in the iris; coloured part of the eye as well as the total light that reaches the eyes. When eyes are exposed to a brighter light, pupils get constricted (smaller) naturally which prevents excess light from entering the eyes whereas in dim and dark setting, pupils dilate (expand/enlarge) allowing more light to enter which adjusts our vision/sight to the surrounding.

In general, size of normal pupil ranges between 2-and-4 millimetres in brighter light whereas 4-and-8 millimetres in dark but as we age, pupil size gets smaller which is a natural process. A research performed on individuals ranging between the age of 18 and 34 years concluded about pupil size:

  • Approximately 3.35 millimetre in direct light when eye is exposed for around 15-seconds
  • More or less 3.86 millimetre in normal/average lighting
  • Nearly 6.41 millimetre in near-complete darkness

Just in-case the pupils are significantly larger than any of the above stats, this is surely the condition referred to ‘dilated pupil’. Even a widened (dilated) pupil can react to light sometimes and shrinks further however, this isn’t always the case. An already enlarged pupil which is completely unresponsive or intact when exposed to light is known as “fixed dilated pupil”.

It must be noted that this anomaly shouldn’t be confused with ‘anisocoria’ which is a common condition in which both, eyes or pupils react normally to light with approximately a half-millimetre variance in size. Anisocoria is a benign situation which affects more or less 20% of the world population.

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There’re many different reasons for dilated pupils. Some of the most common are:

  • Medications

Certain prescribed and non-prescribed medicines can impact on the size of the pupil as well their ability to react to light. These medicines are:

  • Decongestants
  • Antihistamines
  • Tricyclic antidepressants
  • Motion sickness pills
  • Anti-nausea and seizure drugs
  • Medication for Parkinson’s Disease
  • Medication containing botulinum toxin that includes botox injections
  • Atropine which is to control myopia and various medical purposes

Eligibility of the person having dilated pupils to undergo Lasik is determined after careful examination by an eye specialist and severity of the onset that can only be treated with a refractive laser therapy.

  • Eye injury

A serious and penetrable eye injury that can damage the iris also cause dilated pupil in the affected eye, giving it an irregular shape. In rare cases, such an injury can also occur during an eye surgery including a complicated corneal transplant or cataract surgery.

  • A brain injury or disease

A stroke, injury to the head and even tumour in the brain also affect eye pupils and the way they react to light whereas the onset can be present in both the eyes. This is the reason sports physicians check athletes’ pupil with a penlight post-traumatic injury sustained during a game or when a patient is reported to the hospital’s emergency department besides the possibility of stroke symptoms.


Even the slightest eye anomaly should be reported immediately to the doctor for timely diagnosis and appropriate treatment.

Author Bio:

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