• Dilated Pupils

5 Causes of Dilated Pupils: What Is Mydriasis?

Most of the time, our eyes show a nor­mal pupil size. Patients under­stand that pupil dila­tion (when pupils become larg­er) occurs in low light and will shrink in bright light.

Pupils will return to their nor­mal size in time and with­out treat­ment. But, many patients are under­stand­ably con­cerned when their pupils, or those of a fam­i­ly mem­ber, sud­den­ly enlarge and remain that way. Read on to learn about the caus­es of dilat­ed pupils.

Why Do Pupils Dilate and Stay That Way?

There are many caus­es for dilat­ed pupils that don’t return to their nor­mal size. They include:

  • Sex­u­al attrac­tion
  • Eye dis­eases
  • Eye or head injury
  • Med­ica­tion use
  • Illic­it drug use
  • Hor­mon­al imbal­ance (e.g. increase in the hor­mone oxy­tocin)

Get med­ical help imme­di­ate­ly if you or some­one you are with expe­ri­ences sud­den pupil dila­tion after an acci­dent, or has dilat­ed pupils accom­pa­nied by con­fu­sion. These might be signs of brain injury or stroke.

5 Causes of Dilated Pupils

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  1. Dilated Pupils Might Be a Sign of Sexual Attraction

Let’s start with a fun fact: pupil dila­tion that’s not caused by mov­ing to dim lights can be a sign of attrac­tion to some­one near­by. 

Oxy­tocin, the “love hor­mone” is one of the caus­es of dilat­ed pupils. So, if you look into the eyes of your spouse or sig­nif­i­cant oth­er dur­ing “alone time” and his or her eyes dilate, that means he or she finds you attrac­tive. For most peo­ple, this is a heart­en­ing sign, right?

But like so much in med­i­cine and life, it depends on the con­text. 

Both het­ero and gay men are sus­cep­ti­ble to pupil enlarge­ment when they see a man or woman they find attrac­tive. If you’re out with your guy and notice his eyes are dilat­ed when you return from the restroom, he’s prob­a­bly noticed some­one else. Before you break out into “love­hap­py,” take a look to see if he’s eat­ing or check­ing out the food whizzing by. The eyes in hun­gry peo­ple will dilate when they see some­thing appe­tiz­ing. 

Women’s pupils often dilate when they see any­one they con­sid­er attrac­tive, regard­less of their own sex­u­al ori­en­ta­tion. So if your girlfriend’s pupils sud­den­ly get big­ger, don’t spin and look for Idris Elba or Kris­ten Stew­art. You’ll have to trust her. 

  1. Mydriasis and Mydriasis-related Diseases

What is mydri­a­sis? Also called benign episod­ic uni­lat­er­al (or pupil­lary) mydri­a­sis, it’s the diag­no­sis when one eye dilates. It’s con­sid­ered (and labeled) benign because it usu­al­ly isn’t linked to a severe prob­lem. It will often come with blur­ry vision and a headache, and it’s been observed in younger women suf­fer­ing from migraine.

The sin­gle eye dila­tion can last for hours or even days, but it will return to nor­mal pupil size with­out treat­ment.

Not sur­pris­ing­ly, peo­ple with mydri­a­sis are sen­si­tive to light, par­tic­u­lar­ly those who are migraine suf­fer­ers. We rec­om­mend wear­ing sun­glass­es when they are out­doors and get pho­tochromic lens­es that dark­en when exposed to bright light and sun­light if they wear glass­es. 

(Note: pho­tochromic lens­es do not dark­en inside cars with win­dows that have been even light­ly tint­ed.)

Peo­ple whose mydri­a­sis is not caused by oth­er eye dis­eases, med­ica­tion, or injury may be pre­scribed a low dose of Pilo­carpine, a pre­scrip­tion med­ica­tion used to treat glau­co­ma to con­strict the pupils.

Some oth­er dis­eases are known caus­es for dilat­ed pupils:

  • Adie’s pupil is a neu­ro­log­i­cal dis­or­der where one pupil is larg­er than the oth­er and is slow to react to light or lack of light. It some­times occurs with surgery or trau­ma, infec­tion, or poor blood cir­cu­la­tion.
  • Con­gen­i­tal aniridia occurs in peo­ple born with­out an iris or a par­tial one. It usu­al­ly affects both eyes. Many patients have an incom­plete optic nerve or reti­na as well as glau­co­ma or cataracts. 

Both of these con­di­tions are rare. There are no treat­ments for them, but treat­ing the under­ly­ing caus­es such as infec­tions and low blood pres­sure might lessen some of the symp­toms of Adie’s. 

  • Stroke and brain tumors can also cause pupil dilata­tion. This is why doc­tors and first respon­ders will imme­di­ate­ly shine a light into the eyes of acci­dent and trau­ma vic­tims. Doc­tors also look at pupils dur­ing rou­tine phys­i­cal exams as well; an irreg­u­lar-shaped pupil may indi­cate an aneurysm or neck tumor.
  1. Medications and Illicit Drug Use Can Lead to Pupil Dilation

If you’re a par­ent, check­ing your young­sters’ eyes can be an excel­lent way to deter­mine what they have been up to the past few hours. Amphet­a­mines, ecsta­sy, cocaine, and LSD cause pupil dila­tion. On the oth­er hand, so does a num­ber of drugs tak­en for legit­i­mate med­ical rea­sons, includ­ing:

  • Anti­his­t­a­mines, which are often need­ed to relieve itchy eyes caused by aller­gens
  • Decon­ges­tants
  • Med­ica­tions for motion sick­ness
  • Anti-seizure med­ica­tions

The neu­ro­tox­ins in Botox can also cause pupil enlarge­ment. 


Most physi­cians won’t treat pupils that have dilat­ed as a reac­tion to pre­scribed med­ica­tion but instead allow the med­ica­tion to wear off and pre­scribe a dif­fer­ent drug. 

  1. Head and Eye Injury Can Cause Mydriasis

Eyes are del­i­cate, and it’s not sur­pris­ing to learn that they can be eas­i­ly injured with long-last­ing con­se­quences includ­ing mydri­a­sis. An injury that pen­e­trates the eye can dam­age the nerves that con­trol pupil dila­tion.

A head injury can affect the eyes. Pres­sure on the brain can eas­i­ly affect the eye in many ways, includ­ing dila­tion. Dam­age to the third cra­nial nerve, which con­trols eye mus­cles, can result in mydri­a­sis as well. 

Physi­cians who are treat­ing injury vic­tims will close­ly mon­i­tor their eyes for signs of addi­tion­al injury that may require surgery. Surgery can often repair eye dam­age. Fol­low-up care includes wear­ing eye­patch­es, med­ica­tion, and eye drop treat­ment.

  1. Lack of Norepinephrine Can Be Behind Some Dilated Pupils Causes

As we not­ed in the first fact above, oxy­tocin is just one hor­mone known to cause pupils to dilate. Research has sug­gest­ed that pupil size changes with con­cen­tra­tion. The hor­mone nor­ep­i­neph­rine is thought to be behind pupil dila­tion in these instances. 

A study of that tracked pupil sizes among chil­dren with atten­tion deficit hyper­ac­tiv­i­ty dis­or­der (ADHD) report­ed in 2017 that their pupils enlarged when they were con­cen­trat­ing on mem­o­ry-relat­ed tasks. The con­trol group was chil­dren who didn’t take any ADHD med­ica­tion for 24 hours before the research began.

  • All chil­dren showed pupil enlarge­ment dur­ing times of high con­cen­tra­tion includ­ing their ini­tial intro­duc­tion to the exer­cise and lat­er when con­cen­trat­ing to recall the steps.
  • Chil­dren who took methylphenidate (Rital­in) per­formed bet­ter on tasks and main­tained enlarged pupils. Rital­in reg­u­lates and speeds up brain activ­i­ty pow­ered by nor­ep­i­neph­rine

The researchers believe a drop in nor­ep­i­neph­rine can lessen con­cen­tra­tion, and that pupil enlarge­ment is a sign of enhanced con­cen­tra­tion. Changes in pupil size dur­ing peri­ods of con­cen­tra­tion may some­day be a phys­i­cal mark­er for ADHD.

If you’re con­cerned about unusu­al changes in pupil size that are not asso­ci­at­ed with a recent injury or ill­ness (those require emer­gency med­ical atten­tion), give us a call at 888–678-4341. We can answer your ques­tions right away, or sim­ply sched­ule an appoint­ment with us.

July 11th, 2019|Comments Off on 5 Causes of Dilated Pupils: What Is Mydriasis?

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