Although it is normal for dilation to occur based on changes in light, mydriasis could be a sign of an eye injury or problem within the brain, like a head injury, tumor or stroke. Contact your healthcare provider if you experience any of the following: Dizziness, headache or confusion (signs of a stroke).
Doctors sometimes refer to more pronounced mydriasis, when the pupils are fixed and dilated, as “blown pupil.” This condition can be a symptom of an injury to the brain from physical trauma or a stroke. The opposite of mydriasis is called miosis and is when the iris constricts to cause very small or pinpoint pupils.
Miosis can occur in one or both eyes. When it affects only one eye, it's also called anisocoria. Another name for miosis is pinpoint pupil. When your pupils are excessively dilated, it's called mydriasis.
Mydriasis is due to stimulation of the iris dilator muscle or compromise of the parasympathetic tone of the iris sphincter muscle, or both.
MyDriasis has a D, D for dilates the pupil. Mydriasis is a bigger word, so it stands for big pupil (dilated pupil). Miosis is a smaller word, and therefore is a constricted pupil.
Potential causes of unusual mydriasis include injury to the muscles or nerves of the eye, traumatic brain injury, increased levels of oxytocin, and side effects of certain recreational drugs or prescribed medications. Additionally, there are also certain conditions that may result in mydriasis.
The opposite of mydriasis is when pupils constrict and get smaller. This is called miosis.
Miotics (drugs that cause the pupil to contract) improve the outflow of aqueous as part of the treatment of glaucoma and reduce the risk of a posteriorly luxated lens entering the anterior chamber.
Topical mydriatics are used during an eye examination to allow visualization of the retina and other structures deep within the eye. Mydriatics may also be used to treat inflammatory eye conditions such as iritis and cyclitis and to reduce cycloplegia (a painful paralysis of the ciliary muscle of the eye).
Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output.
The parasympathetic nervous supply which causes constriction of the pupil, or miosis, is supplied by cranial nerve III, the oculomotor nerve. Damage to this nerve typically manifests itself as mydriasis, because the sympathetic supply to the pupil which causes mydriasis remains unaffected, and therefore unopposed.
Mydriasis is a consistent sign of glaucoma, and intraocular pressure should be measured in all patients with dilated pupils. The most common cause of glaucoma in critically ill patients is anterior uveitis. Glaucoma is painful and blinding, and steps should be taken immediately to lower intraocular pressure.