What can dilated pupils indicate?

In darkness, the pupils are dilated to allow as much light as possible to enter the eye. The so-called sympathetic nervous system dilates the pupils. It is particularly active during stress reactions and also increases pulse and blood pressure, for example.

In stressful situations, the pupils can dilate accordingly. A negative situation is not necessarily responsible for this. The pupil also appears to dilate when there are pleasant stimuli, such as looking at a loved one.

How strong this effect is, however, is disputed in science. Various substances, including prohibited intoxicants, can dilate the pupils. These include cocaine or methamphetamines, for example. But even the ophthalmologist may give special drops during certain examinations, which dilate the pupils.

What can narrowed pupils indicate?

In bright light, the pupil is constricted to reduce the amount of light entering the eye. But the pupil can also be constricted for other reasons. For example, the pupil seems to narrow when viewing images that are perceived as disgusting or unpleasant.

Narrowed pupils have also been shown to occur under very high mental exertion. Whether and to what extent the pupil narrows or dilates considerably due to different situations or stimuli alone is, however, controversial in science. Severe fatigue can be a trigger for narrowed pupils.

The pupil can also be constricted in various diseases. In most cases there is damage to the areas of the brain responsible for controlling the pupil. These include meningitis or strokes.

The control of the pupil is also disturbed in the so-called Horner syndrome. The nervous system is no longer able to dilate the pupil of the affected eye, the pupil appears to be constricted. Finally, there are a number of substances that can narrow the pupil. These include various painkillers such as morphine, but also certain eye drops, for example for glaucoma.

How do the pupils change with drug use?

Many drugs also have an effect on the width of the pupil. The reason for this is that the pupil width is controlled by parts of the nervous system that can react strongly to given drugs. Some drugs can even act directly on the eyes and affect the pupil width there.

Basically one can distinguish between substances that dilate the pupils and those that narrow the pupil. Substances that dilate the pupil are typically stimulants such as cocaine or amphetamines. Both substances act through a similar mechanism.

They increase the concentration of the messenger substances norepinephrine and adrenaline in the synapses. This has an activating and euphoric effect on the nervous system. In the eye, however, noradrenaline and adrenaline have a pupil-dilating effect.

Substances that narrow the pupils are typically opioids such as heroin or strong painkillers. They have a rather dampening effect on the nervous system. Under the influence of opioids, certain parts of the nervous system cause the pupil to narrow. Although the pupil may react to drugs, the pupil width alone is not a clear indicator of whether a person is under the influence of drugs. You can find more interesting information on this topic at Which drugs or medications influence the pupil?