The Must Know Side Effects of Eye Dilation

The Must Know Side Effects of Eye Dilation

What’s going to happen when those dilating drops are placed in your eyes? Well, the major effect is your pupil will look larger. But having a bigger pupil isn't just cosmetic, it will have some major effects on your vision.

Dilation will have side effects for everyone. This includes making it more difficult to see up close, making things more blurry and making you more sensitive to light. And there are a few more very rare side effects that can happen (but probably won’t) that are good to learn about.

This can even include symptoms that involve your whole body! The dilating eye drops are medications after all. But those are highly unusual. The vast majority of things that you will notice happen to your eyes and your vision.

Side Effects Everyone Has

Dilating eye drops make your pupil bigger. (see also What Does Dilating The Eyes Do?) And making your pupil bigger will cause changes in your vision. Now, because everyone has different eyes and different prescriptions, this will effect everyone a little bit different.

Trouble Reading Up Close

When we are young, the natural lens inside our eye gives us the ability to read up close. It does this by changing shape. But the lens can’t do this task all alone. It it controlled by the ciliary body muscle within our eye. When we want to read up close, this muscles tightens and the lens becomes more spherical changing our focus to see up close.

One common type of medications used to dilate the eyes are known as cycloplegics. This particular type of medication not only causes dilation of the eyes, but it also temporarily prevents this muscle, the ciliary body, from functioning.

So naturally, if we have an eye drop that prevents this muscle from working, we lose our ability to see up close.

Note: this loss of the ability to see up close happens when your vision is corrected with your glasses or contact lenses. If you are naturally nearsighted (without glasses up close is sharp but distance vision is blurry), you will still be able to see up close without glasses but as soon as you put your glasses on, your up close will be blurry.

Blurry Vision

Some people will have more difficulty seeing with dilated eyes. This can be due to a few different reasons:

  • Some people may be farsighted and not really know it. How come? Because the natural lens inside their eye is working to correct that farsighted prescription for them. This constant focusing of the lens allows them to see off in the distance and while they are young enough up close as well. But if we suddenly prevent the ciliary body from controlling this lens (see the side effect above of trouble reading up close), than this lens can’t focus through their farsighted prescription anymore. This will cause their distance vision to also become more blurry.
  • Even if you are wearing your glasses after dilation, you still can have some blurred vision. The optics of the eye work best when the pupil is a certain size. This is because the eye doesn’t have perfect optics. When the pupil becomes too large, you can have light that reaches the retina out of focus. Light that enters the side of our cornea typically is blocked by our undilated iris. When the iris is dilated, this light can reach the retina. This light is out of focus from light that passes through the center of our cornea. This creates something called spherical aberration and can add some blurriness to your vision (and extra halos around lights at night). The older you are, the more of this spherical aberration you can have blurring your vision.
  • Finally, as the lens inside your eye gets older, it can start to get cloudy and become a cataract. Certain types of cataracts scatter light more than others. And exposing more of these cataracts through dilation of the eyes can cause vision to become more blurry.

All these effects which blur vision will be different for everyone. Some people, such as those that are farsighted will notice a lot more blurred vision than others such as young individuals.

Sensitivity To Light

What happens if you shine a light in your eye? Your pupil gets smaller. We have a natural response to prevent extra light from entering our eyes.

So what happens when you shine a light in the eye after the pupil is artificially dilated? You are more sensitive to the light. You can’t constrict your pupil to prevent that extra light from entering. That light will be brighter and can be more uncomfortable for you.

Indoor lights will seem brighter. But if its daytime, outdoor lights will be especially bright. You will want to wear sunglasses after having your eyes dilated to allow you to be more comfortable. And fortunately eye clinics will often provide a cheap pair of plastic disposable sunglasses to wear home.

Roll up disposable sunglasses found in eye clinics; Image courtesy of

Rare Increase In Pressure

The pressure of our eye is determined by a liquid within our eye called aqueous humor. This liquid is constantly being produced and constantly being drained out of the eye at the corner or angle of our iris and our cornea.

Flow of Aqueous Humor within the eye

Flow of Aqueous Humor within the eye;, Public domain, via Wikimedia Commons

When the eye is dilated, it is possible that the iris could bunch up and close off this drainage pathway. This will lead to the pressure inside the eye going high and causing something called angle closure glaucoma. This leads to pain, blurry vision and a red eye.

This sounds worrisome! But fortunately incredibly rare. In fact, it may even be close to zero risk with the short-acting dilating drops that are used today. So really not something to worry about.

The Effect of Eye Drops On The Body

Dilating eye drops are considered very safe. Thousands of individuals a day get these eye drops without having any issues at all. But dilating eye drops can effect more than just the eyes. These eye drops can absorb into the body to cause additional side effects.

The cycloplegic dilating drops (the ones which prevent the ciliary muscle from working) fall into a class of medication which block acetylcholine receptors. This gives these medications something known as anticholinergic effects. What are some of these effects?

  • Dizziness or disorientation
  • Nausea
  • Dry Mouth
  • Even changes in thinking including delirium

Fortunately these side effects are virtually zero for the short-acting dilating drop (tropicamide). And this is the drop commonly used when the eyes are dilated in the office for an exam or for when undergoing eye surgery.

But there are longer-acting dilating drops used for other therapeutic purposes. This includes cyclopentalate and atropine. And it is good to be aware of and let your doctor know if you do have any of these extra side effects from these eye drops.


Dilating your eyes for an eye exam or surgery will cause extra effects in your vision. This can make it more difficult to see and make you more sensitive to light. There can be some additional side effects outside of changes in your vision, but these are very very rare.

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