Table of ContentsView AllTable of ContentsWhat Is the Pupil?Testing Pupil SizeAssociated ConditionsPupil Size and LASIK
Table of ContentsView All
View All
Table of Contents
What Is the Pupil?
Testing Pupil Size
Associated Conditions
Pupil Size and LASIK
Normal pupil size ranges between 1/16 to 5/16 of an inch (2.0 to 8.0 millimeters), depending on the lighting.
The size of your pupil can tell your healthcare provider quite a bit about your health. It’s an important key to unlocking possible medical conditions you might not otherwise know about.
There are manyparts of the eye, and the pupil is among the most important. It controls the amount of light that enters your eye. It also continually changes size.
Your pupil naturally widens and narrows based on the brightness of the light around you. It also changes size depending on whether you are looking at near or far objects.
This article discusses how the size of your pupils can give healthcare providers clues about your health and help them diagnose medical conditions.
Verywell
The pupil is the round, black circle in the center of theiris. Your iris is the colored part of your eye. The pupil is actually a hole through which light passes to theretina, the light-sensitive layer in the back part of the eye.
Your pupils are similar to a camera aperture. They widen or narrow to let more or less light in. Pupils can expand to become larger (dilate) orcontract to become smaller(constrict).
Your iris contains muscles that respond to outside stimuli to control the amount of light that reaches your retina.In bright light, the pupil constricts to reduce the amount of light entering the eye. In dark or dim light, the pupil dilates to allow more light into the eye so you can see better. Dilated pupils—calledmydriasis—range from 4 to 8 millimeters in size.
Your pupils also constrict slightly to look at close objects and dilate slightly to look far away.
The younger you are, the larger your pupils tend to be in normal light.
Although it is rare, some people can have naturally larger pupils. People with naturally large pupils are prone to light sensitivity. The larger pupil allows more light in the eye, which can be uncomfortable but not harmful.
The Function of the Pupil
When your healthcare provider examines your pupils, they will first look foranisocoria—a condition in which the pupils aren’t the same size.Twenty percent of the general population has slight anisocoria that does not signal anything abnormal. But in some cases, unequal pupil sizes can be a symptom of a health condition, such as a brain aneurysm, cluster headache, or stroke.
Pupil Size and Your Health
The optic nerve andoculomotornervesboth control pupil size. These nerves receive some of their messages from the autonomic nervous system. This part of the nervous system controls all of your vital functions, many of which are automatic.
A disruption of the autonomic nervous system might cause changes in how your pupils react to stimuli. That’s why the size of your pupils can indicate health conditions completely unrelated to your eyes.
Pupil size abnormalities can sometimes mean you have a disease or health condition. This is just a small sample of medical conditions you could have. There are also other conditions that can cause irregular pupil function.
Conditions include:
In addition, recreational drugs and alcohol can cause the pupils to dilate or constrict abnormally.This is the reason why healthcare providers check your pupils when there is a concern about intoxication or overdose.
Some prescription and over-the-counter medications, including antihistamines and a few medications used to treat glaucoma, can sometimes dilate your pupils as well.
A Word From Verywell
—ANDREW GREENBERG, MD, MEDICAL EXPERT BOARD
How Pupil Size Affects LASIK Surgery
It is possible that the size of your pupils can prevent you from havingLASIK eye surgeryto correct your vision.People with very large pupils are generally not good candidates for LASIK and other refractive procedures.
Eye specialists may use a device called an infrared pupillometer to measure the size of the pupils. The device consists of a large camera that shines infrared light (an invisible type of light) on the eye and senses the reflected light.
Having naturally large pupils or pupils that dilate heavily in dim light may increase the chances of glare and halos following LASIK. This would interfere with the clear vision you are hoping for from the surgery. For this reason, measuring pupil size is an important step in deciding if LASIK is right for you.
Summary
The size of your pupils can give your healthcare provider clues about your health. Pupil size constantly changes according to the amount of light entering it. It also changes depending on whether the objects you are looking at are near or far away.
When your healthcare provider notices your pupils aren’t acting normally, it indicates you may have a medical condition, or that you may be under the influence of recreational drugs or alcohol.
If your healthcare provider notices that you have naturally large pupils, you probably are not a candidate for LASIK surgery. That’s because people with naturally large pupils may experience glares and halos following a LASIK procedure.
16 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94–106. doi:10.3758/s13428-017-1007-2Aguirre GK.A model of the entrance pupil of the human eye.Sci Rep. 2019;9(1):9360. doi:10.1038/s41598-019-45827-3Michigan Medicine.Eye anatomy and function.Spector RH.The Pupils. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 58.American Academy of Ophthalmology.Why are my pupils so naturally large?MedlinePlus.Anisocoria.LaRoche MJ.Anisocoria and an array of neurologic symptoms in an adult with Ewing sarcoma.J Adv Pract Oncol. 2017;8(1):18–23. doi:10.6004/jadpro.2017.8.1.2U.S. National Library of Medicine.What kinds of eye examinations are there?April 20, 2016.McDougal DH, Gamlin PD.Autonomic control of the eye.Compr Physiol. 2015;5(1):439–473. doi:10.1002/cphy.c140014Johns Hopkins Medicine.Pupillary disorders including anisocoria.American Academy of Ophthalmology.4 neuro conditions not to be missed. March 23, 2016.Brigham And Women’s Hospital.What is a brain aneurysm?Liu SL, Nie YH, He T, Yan XX, Xing YQ.Iris metastasis as the first sign of small cell lung cancer: a case report.Oncol Lett. 2017;13(3):1547–1552. doi:10.3892/ol.2017.5648Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM.Pupillary reactivity as an early indicator of increased intracranial pressure: the introduction of the Neurological Pupil index.Surg Neurol Int. 2011;2:82. doi:10.4103/2152-7806.82248Peragallo J, Biousse V, Newman NJ.Ocular manifestations of drug and alcohol abuse.Curr Opin Ophthalmol. 2013;24(6):566–573. doi:10.1097/ICU.0b013e3283654db2Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB.Pupil size and quality of vision after LASIK.Ophthalmology. 2003;110(8):1606-14.Additional ReadingDoran M, Karmel M, Stuart A.4 neuro conditions not to be missed. American Academy of Ophthalmology. 2012.
16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94–106. doi:10.3758/s13428-017-1007-2Aguirre GK.A model of the entrance pupil of the human eye.Sci Rep. 2019;9(1):9360. doi:10.1038/s41598-019-45827-3Michigan Medicine.Eye anatomy and function.Spector RH.The Pupils. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 58.American Academy of Ophthalmology.Why are my pupils so naturally large?MedlinePlus.Anisocoria.LaRoche MJ.Anisocoria and an array of neurologic symptoms in an adult with Ewing sarcoma.J Adv Pract Oncol. 2017;8(1):18–23. doi:10.6004/jadpro.2017.8.1.2U.S. National Library of Medicine.What kinds of eye examinations are there?April 20, 2016.McDougal DH, Gamlin PD.Autonomic control of the eye.Compr Physiol. 2015;5(1):439–473. doi:10.1002/cphy.c140014Johns Hopkins Medicine.Pupillary disorders including anisocoria.American Academy of Ophthalmology.4 neuro conditions not to be missed. March 23, 2016.Brigham And Women’s Hospital.What is a brain aneurysm?Liu SL, Nie YH, He T, Yan XX, Xing YQ.Iris metastasis as the first sign of small cell lung cancer: a case report.Oncol Lett. 2017;13(3):1547–1552. doi:10.3892/ol.2017.5648Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM.Pupillary reactivity as an early indicator of increased intracranial pressure: the introduction of the Neurological Pupil index.Surg Neurol Int. 2011;2:82. doi:10.4103/2152-7806.82248Peragallo J, Biousse V, Newman NJ.Ocular manifestations of drug and alcohol abuse.Curr Opin Ophthalmol. 2013;24(6):566–573. doi:10.1097/ICU.0b013e3283654db2Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB.Pupil size and quality of vision after LASIK.Ophthalmology. 2003;110(8):1606-14.Additional ReadingDoran M, Karmel M, Stuart A.4 neuro conditions not to be missed. American Academy of Ophthalmology. 2012.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94–106. doi:10.3758/s13428-017-1007-2Aguirre GK.A model of the entrance pupil of the human eye.Sci Rep. 2019;9(1):9360. doi:10.1038/s41598-019-45827-3Michigan Medicine.Eye anatomy and function.Spector RH.The Pupils. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 58.American Academy of Ophthalmology.Why are my pupils so naturally large?MedlinePlus.Anisocoria.LaRoche MJ.Anisocoria and an array of neurologic symptoms in an adult with Ewing sarcoma.J Adv Pract Oncol. 2017;8(1):18–23. doi:10.6004/jadpro.2017.8.1.2U.S. National Library of Medicine.What kinds of eye examinations are there?April 20, 2016.McDougal DH, Gamlin PD.Autonomic control of the eye.Compr Physiol. 2015;5(1):439–473. doi:10.1002/cphy.c140014Johns Hopkins Medicine.Pupillary disorders including anisocoria.American Academy of Ophthalmology.4 neuro conditions not to be missed. March 23, 2016.Brigham And Women’s Hospital.What is a brain aneurysm?Liu SL, Nie YH, He T, Yan XX, Xing YQ.Iris metastasis as the first sign of small cell lung cancer: a case report.Oncol Lett. 2017;13(3):1547–1552. doi:10.3892/ol.2017.5648Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM.Pupillary reactivity as an early indicator of increased intracranial pressure: the introduction of the Neurological Pupil index.Surg Neurol Int. 2011;2:82. doi:10.4103/2152-7806.82248Peragallo J, Biousse V, Newman NJ.Ocular manifestations of drug and alcohol abuse.Curr Opin Ophthalmol. 2013;24(6):566–573. doi:10.1097/ICU.0b013e3283654db2Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB.Pupil size and quality of vision after LASIK.Ophthalmology. 2003;110(8):1606-14.
Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94–106. doi:10.3758/s13428-017-1007-2
Aguirre GK.A model of the entrance pupil of the human eye.Sci Rep. 2019;9(1):9360. doi:10.1038/s41598-019-45827-3
Michigan Medicine.Eye anatomy and function.
Spector RH.The Pupils. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 58.
American Academy of Ophthalmology.Why are my pupils so naturally large?
MedlinePlus.Anisocoria.
LaRoche MJ.Anisocoria and an array of neurologic symptoms in an adult with Ewing sarcoma.J Adv Pract Oncol. 2017;8(1):18–23. doi:10.6004/jadpro.2017.8.1.2
U.S. National Library of Medicine.What kinds of eye examinations are there?April 20, 2016.
McDougal DH, Gamlin PD.Autonomic control of the eye.Compr Physiol. 2015;5(1):439–473. doi:10.1002/cphy.c140014
Johns Hopkins Medicine.Pupillary disorders including anisocoria.
American Academy of Ophthalmology.4 neuro conditions not to be missed. March 23, 2016.
Brigham And Women’s Hospital.What is a brain aneurysm?
Liu SL, Nie YH, He T, Yan XX, Xing YQ.Iris metastasis as the first sign of small cell lung cancer: a case report.Oncol Lett. 2017;13(3):1547–1552. doi:10.3892/ol.2017.5648
Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM.Pupillary reactivity as an early indicator of increased intracranial pressure: the introduction of the Neurological Pupil index.Surg Neurol Int. 2011;2:82. doi:10.4103/2152-7806.82248
Peragallo J, Biousse V, Newman NJ.Ocular manifestations of drug and alcohol abuse.Curr Opin Ophthalmol. 2013;24(6):566–573. doi:10.1097/ICU.0b013e3283654db2
Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB.Pupil size and quality of vision after LASIK.Ophthalmology. 2003;110(8):1606-14.
Doran M, Karmel M, Stuart A.4 neuro conditions not to be missed. American Academy of Ophthalmology. 2012.
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