Dilating drops allow doctors a better view into the eye, make it easier to perform eye surgery, and relieve the pain of some eye diseases, like uveitis, an inflammation of the uvea in the eye. Drops used to dilate eyes are called mydriatics. Cycloplegic drops are a type of mydriatic drop; cycloplegics paralyze the ciliary muscles to keep the pupil dilated. Some dilating drops combine mydriatics and cycloplegics. Like any medication, dilating drops can cause side effects. Side effects of cycloplegics are longer lasting and potentially more serious.
Dilating drops can sting and burn when first inserted. This effect normally lasts only a minute or two, according to the Mayo Clinic. Eye irritation or reddening may occur. Drops that are strictly mydriatics, with no cycloplegic drug added, like phenylephrine, dilate the eye for several hours. The side effects of pupil dilation are light sensitivity and blurred vision. Headache and pain in the brow can also occur, according to the Mayo Clinic.
Cycloplegic drugs paralyze the ciliary muscles of the eye and keep the pupil open longer. Atropine, a cycloplegic, is a drug that has long lasting effects; if atropine is given, the pupil may stay dilated for two weeks, according to the Mayo Clinic. Eyes may water or redden from cycloplegic drops, also according to Mayo, and eyelids may swell. Cycloplegics can cause a serious rise in intra-ocular pressure in people with narrow angle glaucoma, which is fluid buildup behind the colored part of the eye, the iris, according to Aging Eye Times, and should not be given to people with this condition. Cycloplegics also cause a loss of accommodation in the eye; accommodation is the changing of the curvature of the lens to see objects close up.
Any dilating drop can be absorbed systemically and cause side effects outside the eye. You may experience and rise in blood pressure, dizziness, paleness, headache, a sensation that your heart is pounding, or an erratic heartbeat or rapid heartbeat, according to the Mayo Clinic. Thirst, dry mouth or skin, or unusual tiredness may also occur.