Defnition of Mydriasis

Mydriasis – excessive or persistent dilation of the pupil that is a symptom of ophthalmic or systemic conditions. The ophthalmologist may induce mydriasis, using topical atropine, to examine the inner eye. Therapeutic mydriasis using atropinebased ophthalmic drops is an alternate treatment for amblyopia.


Two eye conditions can cause mydriasis: glaucoma and damage to the iris. In the healthy eye the iris, a muscular membrane, controls the opening of the pupil. Inflammation of or tears in the iris affect its ability to function, which also can result in mydriasis.

Other causes of mydriasis are systemic, involving damage to nervous system structures and functions, and may include traumatic brain injury (tbi), stroke, and medication response such as with narcotic use, which causes the muscles to relax.

Eye disorders often affect only one eye (unilateral mydriasis), whereas systemic conditions typically affect both eyes (bilateral mydriasis). Photophobia (sensitivity to bright light) often accompanies mydriasis as the dilated pupil cannot limit light from entering the eye. Vision impairment depends on the extend of the dilation; a fully dilated pupil prevents focus on near objects.

Diagnostic Path and Treatment

The diagnostic path begins with a basic ophthalmic examination including slit lamp examination and ophthalmoscopy, unless there is clear evidence that the mydriasis results from systemic causes. Tonometry, which measures the pressure within the eye (intraocular pressure), determines whether glaucoma is present.

Tears of the iris are typically apparent when looking at the eye as they distort the iris (the colored portion of the eye). Inflammation of the iris (iritis) often reddens the eye and is apparent with ophthalmoscopy. Further diagnostic measures turn to neurologic examination. Treatment targets the causative condition.


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