Mydriasis

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Classification according to ICD-10
H57.0 Pupillary dysfunction
ICD-10 online (WHO version 2019)
Drug-induced mydriasis of the right eye

Mydriasis (from ancient Greek μυδρίασις ) is the medical name for the unilateral or bilateral widening of the pupil . Based on an average pupil diameter, it can be different. Mydriasis is caused by the contraction of the dilatator pupillae muscle , radial or fan-shaped lines of smooth muscles in the iris of the eye , or by the limitation or failure of its antagonist , the sphincter pupillae muscle ; both are part of the inner eye muscles . Maximum mydriasis is always associated with a round pupil, even if it is narrowed, slit-shaped or transversely oval, depending on the species.

Physiologically normal is bilateral mydriasis in the dark as an adaptation and when looking into the distance. A marked dilation of the pupil also occurs with strong sympathetic activity, for example with excitement in fear, joy or emotional affection.

In addition, it can be of pathological origin as a symptom of an illness or it can also be brought about pharmacologically by drugs, intoxicants, plant poisons or the like. Pathophysiologically, the mydriasis in these cases is based on a paralysis of the parasympathetically innervated sphincter pupillae muscle or the nerves supplying it ( oculomotor nerve ) or a permanent contraction of the sympathetically innervated dilatator pupillae muscle .

It can be a major feature of rare syndromes such as multisystem smooth muscle dysfunction (MSMDS).

Often a mydriasis is brought about by the ophthalmologist medically to better examine the fundus by dropping a pupil-expanding preparation into the conjunctival sac of the eye . This mydriatic mostly has a parasympatholytic effect and causes temporary paralysis of the sphincter pupillae muscle , as well as part of the ciliary muscle . Due to the unhindered incidence of light on the retina , the associated extreme sensitivity to glare and the impaired accommodation , z. B. the ability to participate in road traffic is no longer given for the duration of the effect.

As a rule, short-acting mydriatics are therefore used (e.g. tropicamide ), while atropine, for example, can last for several days. In contrast, the administration of whatever mydriatic is contraindicated in the presence of glaucoma disease or even an acute attack of glaucoma . Atropine, or the juice of deadly nightshade , was instilled in the eyes during the Renaissance for cosmetic reasons, as mydriasis was attractive.

A constriction of the pupil is called miosis .

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