What is mydriasis?
Mydriasis is the dilation of the pupil. This reflex allows vision to adapt to darkness. In some cases, this physiological phenomenon may be the sign of an underlying pathology, trauma or the consumption of certain substances. What are the causes of dilated pupil? When should you be worried? Find out everything you need to know about mydriasis.
Dilated pupils: definition of mydriasis
Mydriasis is a natural phenomenon of the eye which is characterized by pupillary dilation. The pupil designates the small circle in the center of the eye whose diameter varies. This variation in diameter is made according to the light perceived in order to regulate the quantity of light rays that enter the eye. This phenomenon called “accommodation” is essential for clear vision both near and far:
•When the light is too strong, the diameter of the pupil shrinks. We then speak of miosis.
•In the dark, the pupil becomes large in order to capture more light. This is called mydriasis.
Mydriasis and miosis are influenced by two antagonistic muscles, that is to say whose effects are opposite. These are the pupillary sphincter and the pupillary dilator. The pupil sphincter is innervated by parasympathetic nerve fibers, participating in the autonomic nervous system. Its contraction leads to a decrease in the diameter of the pupil. The muscle responsible for mydriasis, the pupillary dilator, is innervated by branches of the sympathetic nerve. Its contraction increases the diameter of the pupil when the eye is facing a weak quantity of light or when looking at a distant object.
What causes dilated pupils?
Mydriasis is a natural phenomenon of the eye which makes it possible to adjust the vision according to the quantity of light, the distance of the objects observed or even the emotions felt. Indeed, pupillary dilation is also possible in case of positive emotion, especially in case of attraction for another person.
Mydriasis is also a physiological reaction in connection with the consumption of alcohol, drugs (cocaine, amphetamines, LSD, ecstasy, etc.) or medication. This is particularly the case when taking antihistamines, tricyclic antidepressants or eye drops used in ophthalmology to perform certain examinations such as the fundus of the eye.
In some cases, mydriasis can be caused by damage to the regions of the brain that control vision, the optic or oculomotor nerve. It can be the result of a stroke, a tumour, an infection in the central nervous system, paralysis of the trigeminal nerve or even an accident resulting in head trauma.
Mydriasis can also be a sign of eye diseases. Indeed, ocular trauma, paralysis of the oculomotor nerves, glaucoma or even congenital diseases can also be linked to abnormal pupil dilation.
Mydriasis: when should you consult?
Being a natural phenomenon, pupillary dilation does not pose a risk to vision or to health in general. However, faced with an episode of abnormal mydriasis, it is strongly recommended to make an appointment with your doctor as soon as possible. A consultation with an ophthalmologist and/or a neurologist may also be necessary in case of suspicion of an underlying pathology. To treat abnormal mydriasis, it is essential to treat the cause. Depending on the cause, pharmacological treatment with eye drops, symptomatic (wearing tinted glasses) or surgical (extraction of the lens and implantation of an artificial lens) may be necessary.
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