Table of ContentsView AllTable of ContentsHow Pupils Change SizeCauses of MydriasisPupil Dilation in Eye ExamsTreatmentWhen to see a doctor
Table of ContentsView All
View All
Table of Contents
How Pupils Change Size
Causes of Mydriasis
Pupil Dilation in Eye Exams
Treatment
When to see a doctor
Mydriasis occurs when thepupilremains dilated (widened) and doesn’t respond to light changes in an environment. It can happen due to an injury, medications, or psychological factors. Usually, the pupil becomes wider to allow more light into your eye in dim environments and gets smaller to prevent light from entering your eye in bright places. The pupil also dilates in response to factors such as touch, sound, and emotion. In people with mydriasis, the pupil will remain dilated even in bright places and in the absence of any stimulus.
Peter Finch / Getty Images
A pupil is the round black circle in the center of the iris. It controls how much light enters the eye before it reaches the retina. The standard pupil size ranges between 2 millimeters (mm) and 8 mm, depending on the lighting.
Stimulation of the sympathetic nervous system, which is known for triggering a fight-or-flight response when the body is under stress, can also cause the pupil to dilate.
What Is Miosis?
Eye Injury
Left Eye Pain: Why It Hurts and How to Relieve It
Traumatic Brain Injury
Mydriasis can occur in people withtraumatic brain injuries. These often increase intracranial pressure, which can put pressure on and affect the eye system. It tends to happen on just one side, and this type of mydriasis is called unilateral fixed mydriasis, or a blown pupil. The presence of a dilated pupil on only one side suggests that a large mass or lesion may be present.
Lasting bilateral mydriasis and the absence of a light reflex in the pupil following a severe traumatic brain injury are considered signs of irreversible brain stem damage and have been strongly associated with poor outcome.
Traumatic Brain Injury (TBI) Causes and Complications
Medications
Mydriasis can also be a side effect of different medications. While systemic medications cause bilateral mydriasis, direct ocular inoculation with topical medications can cause unilateral mydriasis.
Some of the medicines that can cause the problems are:
Exposure to Certain Plants
Some plants have substances such as scopolamine and atropine that can cause mydriasis. The Angel’s trumpet plant, for example, contains hyoscyamine, atropine, and scopolamine, which can dilate the pupil. Plants of the belladonna family and Jimson weed can also cause mydriasis.
Drug Use
Drugs can expand or shrink the eye muscles, causing mydriasis. Substances such as cocaine increase serotonin level, which can lead to pupil dilatation. LSD has a direct effect on serotonin receptors in the brain, which can also cause mydriasis. Other drugs that have a similar side effect are crystal methamphetamine and ecstasy.
Increased Oxytocin Levels
Oxytocin is a hormone. High levels of oxytocin can lead to mild or moderate mydriasis.
Migraine
Migrainescan occasionally cause benign episodic unilateral mydriasis due to hyperactivity of the sympathetic nervous system or hypoactivity of the parasympathetic system.It is a temporary condition and is more common in young women.
Symptoms of a Migraine
Cranial Nerve Neuropathy
Neuropathyis a disorder that impairs the ability to feel and move. When it affects the third cranial nerve, also known as theoculomotor nerve, the pupil becomes fixed and dilated due to paralysis of the iris sphincter.
What Causes Dilated Pupils?
Not all causes of mydriasis are problematic. Optometrists and ophthalmologists often use drops to dilate your pupils during an eye exam. This allows them to examine theoptic nerveandretina. This dilation typically lasts four to six hours, but sometimes a doctor will use a drop that can last 24 hours or more. Other causes, however, may be serious and require treatment.
It often takes up to 30 minutes for a pupil to dilate after receiving the eye drops. Your eye doctor cannot tell you how blurry your vision will be and for how long. That depends on the type of dilating eye drop used and how your eyes react to it.
When your eyes are dilated, they are often extremely sensitive to light. Your vision becomes blurry and you will have trouble focusing on near objects.
How Long Do Pupils Remain Dilated After an Eye Exam?
Treatment will depend on what causes mydriasis. When prescribed medications cause it, the pupils will go back to normal after the effect diminishes and you stop taking the medication. No treatment is required in this case.
To measure the pupil and how it responds to light, an eye care specialist will use a manual or automated pupillometer. The automated pupillometer, which offers a more precise result, is an infrared digital video device that can obtain objective measurements of pupil size and reactivity.
Eye Exams Are Now Recommended Every Year—But Do You Really Need One?
When to See a Doctor
If your pupils don’t change when the light changes or one is noticeably larger than the other, you should talk to your eye doctor. In these cases, mydriasis might be a sign of an eye injury or a problem that affects the brain, like a tumor, stroke, or head injury.
7 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 Feb;50(1):94-106. doi:10.3758/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic brain injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017 Sep 26;8:229. doi:10.4103/sni.sni_299_17Pennington KM, St Louis EK.“Don’t Believe Your Eyes” Ipratropium Induced Mydriasis: A Case Report and Review of the Literature.Gen Med (Los Angel). 2016 Jun;4(3):255. doi:10.4172/2327-5146.1000255Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.American Academy of Ophthalmology.What Are Dilating Eye Drops?Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014 Aug;29(4):599-603. doi:10.1016/j.jcrc.2014.01.012Additional ReadingMathôt 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/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic Brain Injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017;8. PMCID: PMC5629836.Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.Modi P, Arsiwalla T.Cranial nerve iii palsy.In:StatPearls. StatPearls Publishing; P.MID: 30252368American Academy of Ophthalmology.What Are Dilating Eye Drops?Maas RP, Verrips A.Episodic unilateral mydriasis and recurrent headache: Not necessarily an ominous combination.Cephalalgia Reports. doi: 10.1177/2515816318772305.Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014;29(4):599-603. doi: 10.1016/j.jcrc.2014.01.012.American Academy of Ophthalmology.Pharmacologic dilation of pupil.MedlinePlus.Scopolamine Transdermal Patch.
7 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 Feb;50(1):94-106. doi:10.3758/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic brain injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017 Sep 26;8:229. doi:10.4103/sni.sni_299_17Pennington KM, St Louis EK.“Don’t Believe Your Eyes” Ipratropium Induced Mydriasis: A Case Report and Review of the Literature.Gen Med (Los Angel). 2016 Jun;4(3):255. doi:10.4172/2327-5146.1000255Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.American Academy of Ophthalmology.What Are Dilating Eye Drops?Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014 Aug;29(4):599-603. doi:10.1016/j.jcrc.2014.01.012Additional ReadingMathôt 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/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic Brain Injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017;8. PMCID: PMC5629836.Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.Modi P, Arsiwalla T.Cranial nerve iii palsy.In:StatPearls. StatPearls Publishing; P.MID: 30252368American Academy of Ophthalmology.What Are Dilating Eye Drops?Maas RP, Verrips A.Episodic unilateral mydriasis and recurrent headache: Not necessarily an ominous combination.Cephalalgia Reports. doi: 10.1177/2515816318772305.Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014;29(4):599-603. doi: 10.1016/j.jcrc.2014.01.012.American Academy of Ophthalmology.Pharmacologic dilation of pupil.MedlinePlus.Scopolamine Transdermal Patch.
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 Feb;50(1):94-106. doi:10.3758/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic brain injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017 Sep 26;8:229. doi:10.4103/sni.sni_299_17Pennington KM, St Louis EK.“Don’t Believe Your Eyes” Ipratropium Induced Mydriasis: A Case Report and Review of the Literature.Gen Med (Los Angel). 2016 Jun;4(3):255. doi:10.4172/2327-5146.1000255Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.American Academy of Ophthalmology.What Are Dilating Eye Drops?Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014 Aug;29(4):599-603. doi:10.1016/j.jcrc.2014.01.012
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 Feb;50(1):94-106. doi:10.3758/s13428-017-1007-2
American Association of Neurological Surgeons.Traumatic brain injury.
Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017 Sep 26;8:229. doi:10.4103/sni.sni_299_17
Pennington KM, St Louis EK.“Don’t Believe Your Eyes” Ipratropium Induced Mydriasis: A Case Report and Review of the Literature.Gen Med (Los Angel). 2016 Jun;4(3):255. doi:10.4172/2327-5146.1000255
Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.
American Academy of Ophthalmology.What Are Dilating Eye Drops?
Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014 Aug;29(4):599-603. doi:10.1016/j.jcrc.2014.01.012
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/s13428-017-1007-2American Association of Neurological Surgeons.Traumatic Brain Injury.Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017;8. PMCID: PMC5629836.Skeik N, Jabr FI.Migraine with benign episodic unilateral mydriasis.Int J Gen Med. 2011;4:501-503. doi: 10.2147/IJGM.S18613.Modi P, Arsiwalla T.Cranial nerve iii palsy.In:StatPearls. StatPearls Publishing; P.MID: 30252368American Academy of Ophthalmology.What Are Dilating Eye Drops?Maas RP, Verrips A.Episodic unilateral mydriasis and recurrent headache: Not necessarily an ominous combination.Cephalalgia Reports. doi: 10.1177/2515816318772305.Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014;29(4):599-603. doi: 10.1016/j.jcrc.2014.01.012.American Academy of Ophthalmology.Pharmacologic dilation of pupil.MedlinePlus.Scopolamine Transdermal Patch.
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
American Association of Neurological Surgeons.Traumatic Brain Injury.
Athanasiou A, Balogiannis I, Magras I.Lasting bilateral mydriasis after traumatic brain injury may not always be a lost case.Surg Neurol Int. 2017;8. PMCID: PMC5629836.
Modi P, Arsiwalla T.Cranial nerve iii palsy.In:StatPearls. StatPearls Publishing; P.MID: 30252368
Maas RP, Verrips A.Episodic unilateral mydriasis and recurrent headache: Not necessarily an ominous combination.Cephalalgia Reports. doi: 10.1177/2515816318772305.
Zafar SF, Suarez JI.Automated pupillometer for monitoring the critically ill patient: a critical appraisal.J Crit Care. 2014;29(4):599-603. doi: 10.1016/j.jcrc.2014.01.012.
American Academy of Ophthalmology.Pharmacologic dilation of pupil.
MedlinePlus.Scopolamine Transdermal Patch.
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