My pupils are dilated! What now?

Many people have questions about their pupils before, during and after an eye exam, especially after they have been dilated. In this blog post, I will talk about the truly amazing function of your pupils – the little black holes that let light in your eye.

We will discuss:

• Why pupils dilate
• How pupils dilate
• Why sometimes pupils are large
• What medications affect our pupil size
• What we should do if our pupils are large
• When should I worry or seek out an eye doctor about my large pupils
• Did I take something that made my pupils small or large
• Why sometimes one pupil is larger than the other

Pupils are an amazing structure in our eyes that have been created through millions of generations of animals over hundreds of millions of years. They allow us today to see things that even the most expensive cameras in the world have trouble seeing. We can see in extremely low light, extremely bright light, and everything in between. They are affected by your mood, medications, drugs, and of course the ambient light. They change throughout our lives and are very much a part of our personality.

Healthy, normal pupils should constrict briskly and equally to light and dilate when the light is withdrawn. Both pupils should constrict when light is shined in one. This is called the pupillary light reflex, and is an involuntary reaction originating from your brainstem, which is why it’s called a reflex. It doesn’t need you to be conscious, and is a very helpful physical exam sign that should be understood by all doctors, not just eye doctors. If your pupils don’t react normally, your doctor should know the possibilities that the abnormal reaction implies, and know what to do to help.

Some people incorrectly spell dilated “dialated” which is understandable, because it is round like a dial, but it is spelled “dilated.”

There are many reasons to have large pupils. I’ll list as many as I can think of.

• Being young: our pupils tend to be larger when we’re young. Fun fact: women used to put the juice of the belladonna (beautiful woman in Italian) plant in their eyes to make their pupils big and therefore more seductive. Probably also to make men more attractive to them since they’d be blurry. That’s a dad-joke! But the medicine is no joke. The plant is highly toxic.
• Medications/drugs: there is a very long list of medications that can make our pupils bigger, starting with the ones we use to perform a dilated eye exam.
• To dilate our patients’ pupils, we use:
  • Mydfrin- generic name: phenylephrine
  • Mydriacyl- generic name: tropicamide
  • Scopolamine
  • Atropine (usually used therapeutically, not diagnostically-see below)
• Many other medications that affect your nervous system can also make your pupils larger or smaller, although generally the effect is a lot less than what we eye doctors use:
  • Antihistamines
  • Decongestants
  • Parkinson’s medications
  • Motion sickness medications
  • Tricyclic antidepressants
  • Anti-seizure medications
  • Flomax (Tamsulosin) for prostatic hypertrophy can cause “Floppy Iris Syndrome” that can make cataract surgery more difficult.
• Drugs:
  • Cocaine was formerly used to dilate pupils, and is still potentially useful, although difficult to obtain, even for doctors, in the diagnosis of a condition called Horner’s syndrome.
  • LSD
  • Amphetamines
  • Ecstasy
• Mood: although the effect of your mood on your pupils is short-lived, it can either dilate or constrict your pupil.
• Previous eye conditions, eye trauma, or eye surgery that has left your pupils irregular or different looking: Inflammatory conditions such as iritis (inflammation of the iris) that can occur from many different reasons, can leave you with adhesions to the lens of your eye called synechia.  These can sometimes be broken with dilation or a surgical procedure to break the stickiness.
• Congenital (born with it) irregular pupils: such as an iris coloboma, which occurs when your eyes don’t fully develop the iris sphincter in utero (when your mom is pregnant with you). It most frequently occurs in the lower portion of the iris, and has been called a “keyhole” iris.
• A prosthetic eye: if someone has lost an eye, hopefully the prosthetic eye is so real looking that it may not be readily detectable.  If so, the pupillary will of course not dilate, which may make the size of the pupil in the healthy eye a different size. When in a bright or dim environment.

Why do I need to have my pupils dilated?

As a part of a complete eye exam, we put medication in your eyes to relax the pupillary sphincter and/or stimulate the radial muscles of your iris (the colored part of your eyes) to make them large so we can see inside your eye. This allows us to diagnose problems of the retina (the light-sensitive layer that lines the back of our eye and acts like film in a camera (for those of us who remember when cameras had film in them!)

How does pupil dilation help my eye doctor?

The other major reason we dilate your pupils is to refract you. Sounds scary, but it just means we measure your eyes for the amount of farsightedness, nearsightedness, and astigmatism. Your focusing muscles are relaxed with the drops so they don’t affect the measurements. This wears off in a few hours.

Why can’t I see when I have dilated eyes?

The medications we as eye doctors administer to dilate your pupils also relax the focusing muscles that change the shape of the lens of our eyes and add focusing power that we need to see near objects. If you’re nearsighted, you may be able to see better when you remove your glasses. Don’t worry, the effect wears off in a few hours.

Why do pupils dilate?

Anatomically our pupils have two opposing sets of muscles, just like other parts of our bodies. Our triceps oppose our biceps, hamstrings oppose our quadriceps and so on, so we can flex and extend our body parts. Our pupils have a sphincter, a round muscle that pulls the iris centrally like a purse string and makes it smaller. We also have radial muscles of the iris, which are like spokes of a wheel. When they shorten/constrict, they pull the iris away from the center and make our pupils bigger. When we dilate pupils, we give you eye drops that stimulate the radial muscles and relax the sphincter muscles. Et voilà, your pupils enlarge within a few minutes.

Dilated Pupils scared my regular doctor!

In medical shows, and IRL (in real life) you may see the doctor shining a light into an accident victim’s eyes. There are several things that can be determined by this physical exam component. One of the scary ones is pressure on the part of the optic nerve that constricts the pupil. If this constriction is impaired, it may indicate a life-threatening condition such as a ruptured aneurysm, hemorrhagic stroke, or increased intracerebral pressure from a head injury or other trauma. If immediate action is not taken, the patient could quickly die.

I just naturally have big pupils. Why are my pupils so big?

Yes, this occurs in people, generally younger ones, and is part of normal variation in people. Isn’t it wonderful!?

My dilated pupils took days to wear off!

Sometimes this just happens. Generally, the lighter your irises, the longer it takes to metabolize the medications, and it could be that it took that long. Also, there is a medication called Atropine that may have been used. In my practice, I rarely use Atropine eye drops, and I never use it for routine dilation. I use it only when my patient has an inflammatory or traumatic eye condition and we need to relax the eye muscles so their eye can heal. Sort of like putting your arm in a sling if you sprain or break your wrist. Atropine can take up to a week to wear off. There are a couple other similar longer-lasting medications such as Hyoscine and Scopolamine (also used for seasickness).

One of my pupils dilated more than the other one. What’s up with that?

The medical term for different sized pupils is “anisocoria.” There are many reasons for this, but if you don’t know why this is happening, you should definitely let your eye doctor know right away. Sometimes it’s physiologic anisocoria, which just means that’s your normal, but there are many reasons why this may not be normal, and you should have a highly competent eye doctor do a very careful exam. If it’s not normal, figure that out and get the help you need.

I hope this has helped you understand a little more about your pupils, the miraculous little opening in the center of your eyeball that regulates the amount of light entering your eye, helps focus light, and helps you see near objects better.

– Dr. Matthew R. Sharpe