A few words of thanks would be greatly appreciated.

Pupil dilation


Pupil dilation, also called mydriasis, is manifested by a pathological enlargement of the diameter of the pupil, the small black dot in the center of the eye. The pupil is the aperture through which light enters. Two muscles control it: the dilator - which as its name suggests, expands - and the sphincter - that contracts. It is the paralysis of the sphincter that causes mydriasis or other dilating spasms. This pathological pupil dilation can affect one or both eyes. This may be caused by certain medications, such as atropine, some eye drops called mydriatic eye drops (used to facilitate eye examination) or by some neurological diseases. There is however a normal pupil dilation in response to a minor brightness in order for the eye to capture the best possible light rays and increase its vision capacity in the dark.


Mydriasis clinically manifests itself through the expansion of one or both pupils.


Depending on the extent to which one or both eyes are affected, the suspected diagnosis will be different. Bilateral mydriasis with little response to light (constriction) in the context of behavioral disorders and even coma may evoke significant brain damage. This is seen in the case of cardio-respiratory arrest, but also in the case of poisoning with drugs such as cocaine or medicines like antidepressants or atropine. Support is needed urgently in case of a behavioral disorder or a coma. Unilateral mydriasis points more towards sphincter paralysis: an ophthalmological examination will be performed.


Treatment varies depending on the causes of the pupil dilation. The treatment of the cause generally allows a quick return to normal.


The only case of dilation that is possible to prevent is that caused by drugs. In this case, it is essential to read the instructions on medications to know their side effects.

A few words of thanks would be greatly appreciated.

Ask a question
CCM is a leading international tech website. Our content is written in collaboration with IT experts, under the direction of Jeff Pillou, founder of CCM.net. CCM reaches more than 50 million unique visitors per month and is available in 11 languages.