Dilated pupil

What is a dilated pupil?

Dilation of the pupil, also called mydriasis, is the widening of the pupil in one or both eyes.

In ophthalmology, pupil dilation is often induced artificially using special eye drops. The patient is given eye drops that cause the pupillary sphincter (Sphincter pupillae muscle) is temporarily paralyzed. With this measure, the doctor can, for example, assess the fundus and thus recognize diseases or changes in the eye.


The dilation of the pupil is used by the ophthalmologist on the one hand in diagnostics, but on the other hand also in the therapy of certain eye diseases. It is often used diagnostically in children to perform a so-called skiascopy. This examination carried out with the pupil flared enables an objective detection of ametropia.

Ophthalmoscopy is also performed with the pupil dilated. The fundus can be assessed. This is particularly important in order to identify diseases of the retina, for example as a long-term consequence of diabetes mellitus, and those of the optic nerves and blood vessels.

In addition, pupil dilation is used in some forms of therapy. When there is inflammation within the eye, the iris is often also affected.
In the course of the disease, the iris can stick to the pupil, which is not harmless. Synechiae). To prevent this, the pupils are made wide. This can significantly reduce the likelihood of adhesions, as the spatial proximity of the pupil and iris becomes smaller.

In addition, the adaptation of farsighted people to glasses can initially also be carried out with the help of pupil-dilating eye drops, since the pupillary sphincter develops a kind of cramp in the case of long-sighted farsightedness, in order to be able to permanently see nearby. This spasm is released by the dilation of the pupils and the eye can adapt to the glasses.

Learn more about the topic at:

  • Anisocoria
  • different sized pupils


The preparation for a dilatation of the pupil at the ophthalmologist is usually very straightforward. For the examination, the patient should bring a list of the drugs they are currently taking with them in order to avoid interactions with the eye drops used.

Patients with increased intraocular pressure or known glaucoma (glaucoma) must not receive eye drops to dilate their pupils, as this can trigger a so-called glaucoma attack. Contact lenses must also be removed from the eye immediately before the procedure. These should not be used again until some time after the examination.

Find out more about the topic here Glaucoma.


Before dilating the pupil, the doctor will first ask about the most important exclusion criteria (medication and diseases, see above), if these are not already known. The actual action is very quick.

The eye drops are placed in one or both eyes. The patient can then sit in the waiting room again for about 15 minutes until the full effect has occurred. Only then can the actual examination, for which the previous pupil dilation is necessary, be carried out.

Which eye drops are used?

Eye drops are used which, among other things, can cause the pupillary sphincter (Sphincter pupillae muscle) is temporarily paralyzed or that the muscle that actively dilates the pupil (Dilator muscle pupillae) is activated.

The active ingredient tropicamide is most often used for diagnostics, as the effect occurs comparatively quickly and also disappears again.

The following other eye drops are also suitable for diagnostic or therapeutic dilation of the pupil: neosynephrine, cyclopentolate, scopolamine, homatropine or atropine.
The latter in particular is only used in exceptional cases, as the effect can last for several days.

Find out more about the topic here Eye drop.


The dilation of the pupil itself is quite low-risk thanks to modern active ingredients. However, it is important to ensure that you inform the ophthalmologist about known pre-existing conditions. The already mentioned glaucoma in particular is the most important disease in which pupil dilation is not allowed.

Side effects can also occur after the pupil has dilated. In the vast majority of cases, however, these are completely harmless. This includes burning eyes immediately after the drug is put into the eye.

In rare cases, side effects can also affect the whole body. In exceptional cases, a dry mouth or a rapid heartbeat (Tachycardia) come.


The dilatation of the pupil for diagnostic purposes, for example to examine the retina, only takes a few hours, as already mentioned. The day after the examination at the latest, the patient can see completely normally again and is no longer impaired.

However, one or both pupils can be dilated for therapeutic purposes. Especially with inflammation within the eye (e.g. uveitis, an inflammation of the choroid), it may be necessary to dilate the pupils over several hours or days until the risk of adhesion between the iris and the lens is averted.

Investigation costs

The full examination of the eyes, including the retina, costs € 5.83 according to GOÄ. The enlargement of the pupil must be included in the subsequent examination. The costs are usually covered by the respective health insurance company.

What are the alternatives?

As an alternative, some ophthalmological practices now offer examinations with a special camera. In most cases, this can depict the fundus of the eye despite the normally wide pupil, and the doctor can then assess it according to certain criteria. This examination is not possible with very narrow pupils and with cataracts (clouding of the lens).

However, an examination with special cameras is not necessarily covered by the health insurance. This alternative is also not available for dilation of the pupil for therapeutic purposes, since the dilation is supposed to protect against sticking to the lens in the event of inflammation within the eye.

How do I behave after the pupil dilation?

The eye is very sensitive to light immediately after the pupil is dilated. It is recommended to protect the eyes from direct sunlight for the time being. For example, patients should sit with their backs to the sun or wear sunglasses for protection.

In addition, visual acuity is severely limited at the beginning, so that work with heavy equipment or other activities that could lead to injuries in poor visibility should not be carried out at the beginning.
In addition, reading and working in close proximity to the eyes can be difficult in the first few hours after the pupil is dilated, as close-up vision is not yet fully developed.

However, since the full effect of modern pupil-expanding drugs (especially tropicamide) only lasts a few hours, the precautionary measures are limited to the day of the examination at the most.

How long after that am I not allowed to drive a car?

Even driving a car or motorcycle is initially not possible due to the limited visual acuity. The same rules apply here as for operating machines, i.e. Driving is strictly prohibited for the first hours (3-4 hours at least) after the pupil is dilated.

It is recommended not to use a car or motorcycle for the rest of the day in order to minimize any risk for yourself and other road users.

Do the pupils dilate when one is in love - myth or truth?

There are various influences that can cause the pupil to expand or contract. It is particularly interesting that not only light and darkness change the size of the pupils, but also, for example, emotional arousal.
This explains why the pupils can dilate in lovers.

However, it is not only strongly positive feelings that make the pupils dilate; fear, such as is experienced when watching a scary movie or general cognitive activity, such as when solving a difficult puzzle, can dilate the pupil.

Please also read: Which drugs or drugs affect the pupil?