What is the Pupil?
The pupil is the black circle in the middle of the colored portion of the eye, the iris. The pupil is actually a hole that allows light to enter the eye.
The size of the pupil changes due to light, medication, and some disease processes.
A large pupil is considered a dilated pupil and may reach a size of up to ten millimeters across.
Causes of Large Pupils
The cause of a large pupil is important to determine as some causes can indicate a larger disease that is involving the eyes.
If the pupil is large in dim light and then returns to a small size when bright light is shined in the eye or in the room, the large pupil may be completely normal and a result of the iris changing size due to the light.
However, if the pupil is constantly large, even in bright light, it is likely associated with medication or a disease or condition.
Medication that Causes Dilated Pupils
One of the most common eye drops that is used by eye doctors, dilating drops are a type of medication designed to cause the pupils to become large in order to allow the doctor to examine the back of the eye.
These dilating drops are not available over the counter and are only prescribed for at home use in a few eye conditions.
Common medications that are considered dilating eye drops are tropicamide, phenylephrine, atropine, and homatropine.
These dilating drops may be prescribed for eye inflammation, amblyopia in children, and other eye conditions.
The primary affect of these eye drops is to increase the size of the pupil and will typically be very effective and cause a much larger pupil than an eye without the medication.
Medications that Cause Large Pupils as a Side Effect
While there are medications that are designed to increase the size of the pupil, some medications will cause a larger pupil as a side effect rather than the main effect of the medication.
Some medications that can result in large pupils are allergy medication, anxiety and depression medications, and decongestants, such as Visine, among others.
These medications are commonly prescribed or available over the counter. Many of these medications will have a small effect and result in a pupil that is slightly larger than normal but may not be obvious.
However, there is the potential for many of these medications to result in a large dilation and the pupil size to increase greatly.
Diseases that Cause a Dilated Pupil
Having a single large pupil can be a cause for concern of a variety of serious medical conditions including a brain aneurysm, carotid artery blockage, or tumor in the brain.
While there is a possibility of a severe disease that could be causing the large pupil, it is also a possibility that the large pupil is harmless as in Aide’s Tonic Pupil Syndrome.
In order to differentiate between a serious disease or condition or a harmless condition, your eye doctor should complete a comprehensive eye exam and may need to make a referral for imaging of the brain or neck.
What to Do for a Large Pupil
If you notice that one or both of your pupils are larger than normal, consider if you have used any eye drops recently or if you have begun any new medications that list dilated pupils as a result.
If you are not able to identify a cause of the large pupils, schedule an appointment with your eye doctor to complete an entire eye health evaluation to ensure that a serious disease is not responsible for the large pupils.
