Cycloplegics are medications, usually in the form of eye drops, which cause cycloplegia, which is paralysis of the ciliary muscle in the eye. This stops accommodation of the eye, that is focusing for vision at different distances. There are a number of drugs which are cycloplegics including atropine, homatropine, cyclopentolate and tropicamide, all of which differ slightly in potency, onset and duration of action. They are available in most countries by prescription only and trade names may differ from country to country, according to manufacturer.
The mechanism of action of cycloplegics is by their blocking action on the muscarinic receptors in the eye. These receptors are involved in the ocular muscle action so, by blocking them, the cycloplegics prevent the muscles from moving. This not only causes cycloplegia, but also mydriasis, which is dilation of the pupil. The different cycloplegics have different potency with regards to both cycloplegia and mydriasis.
The choice of which of the cycloplegics is used will be made by the doctor, according to the indication for which it is being used. Most commonly they are used to make examination of the eye easy. They may also be used to treat uveitis, a swelling or inflammatory condition of the eye, and to prepare the eye for ophthalmic surgery.
Atropine, homatropine, cyclopentolate and tropicamide all have a slightly different onset of action and their duration of action, both on the pupil and the ciliary muscle differ. The treating doctor will prescribe the most suitable agent on a case-by-case basis. In the case of atropine, the usual dosage regimen for acute inflammatory conditions is instillation three times daily and for preparation before a procedure, the drops may be given less frequently for a couple of days before. The prescribed dose should never be exceeded.
As with any medication, cycloplegics may cause unwanted side effects. These are mainly local effects, due to the topical nature of eye drops, but systemic effects have also been reported. Local adverse effects which have been reported include irritation or burning of the eyes and allergic conjunctivitis. Systemic effects may include flushing, increased heart beat and confusion.
As with any medication, cycloplegics may interact with others, including prescribed, over-the-counter, homeopathic and complementary medicines, so these should be disclosed to the prescribing doctor. The cycloplegics may be contraindicated in people with some underlying clinical conditions, so these should also be discussed with the doctor. They may increase the intra-ocular pressure, so it may be contraindicated in patients with glaucoma.