How Do Ophthalmic Direct-Acting Miotics Work?

Ophthalmic direct-acting miotics are medications that cause constriction (miosis) of pupils by stimulating certain eye muscles to contract. Miosis improves drainage of aqueous humor and reduces the pressure inside the eye (intraocular pressure). Aqueous humor is a clear fluid that fills the space between the lens and the cornea in the eyes.

Ophthalmic direct-acting miotics mimic acetylcholine and stimulate protein molecules known as cholinergic receptors on the eye muscles that contract in response to acetylcholine. Acetylcholine is a chemical (neurotransmitter) that nerve endings in muscles secrete to stimulate muscle contraction.

Ophthalmic direct-acting miotics are used to contract the eye’s ciliary muscle and the sphincter muscle encircling the iris, which constricts the pupil, improves aqueous humor drainage and reduces intraocular pressure. Balancing the inflow and outflow of aqueous humor is necessary to maintain optimum pressure in the eye and the eye’s spherical shape.

Ophthalmic direct-acting miotics are solutions or gels topically administered on the eye surface or solutions injected into the eye. Ophthalmic direct-acting miotics are used to reduce intraocular pressure in the following situations:

After ocular surgeries (such as cataract surgery) which can cause a rise in intraocular pressure.

Elevated intraocular pressure due to imbalance in the production and drainage of aqueous humor.

To treat glaucoma, a progressive disease that damages the optic nerve. Glaucoma is most often characterized by elevated intraocular pressure which can further damage the optic nerve. Reducing intraocular pressure is the primary treatment for glaucoma.

To counteract pupil dilation (mydriasis) caused by pupil-dilating medications.

Side effects of ophthalmic direct-acting miotics may include the following:

Ocular side effects:

• Corneal edema (corneal swelling-buildup of fluid in your cornea)
• Corneal clouding
• Corneal decompensation, a condition in which the innermost corneal layer (endothelium) is affected and can cause corneal opacity
• Prolonged miosis
• Accommodative spasm, a condition caused by a spasm of the ciliary muscle that makes the eye constantly focus on near objects
• Ocular irritation
• Difficulty with sight in low light conditions
• Burning, stinging and itching
• Reduced visual acuity
• Deposits in the middle layer of the cornea (corneal granularity)
• Short-sightedness (myopia)
• Congestion of blood vessels in the conjunctiva, the clear membrane over the whites of the eye and inner eyelid surfaces (conjunctival vascular congestion)
• Tearing (lacrimation)
• Retinal detachment (rare)
• Persistent swelling of cornea (bullous keratopathy)
• Postoperative iris inflammation (iritis) after cataract extraction
• Eye inflammation and pain
• Increased intraocular pressure
• Blood vessel dilation in the eye (ocular hyperemia)
• Blurred vision
• Visual impairment

Systemic side effects:

• Slow heartbeat (bradycardia)
• Low blood pressure (hypotension)
• Flushing
• Breathing difficulty
• Sweating (diaphoresis)
• Temporal headache or brow ache
• Rise in blood pressure (hypertension)
• Rapid heart rate (tachycardia)
• Salivation
• Nausea and vomiting
• Headache
• Bronchial spasm
• Asthma
• Abdominal cramps
• Epigastric distress
• Irregular heartbeat (arrhythmia)
• Fainting (syncope)
• Tightness in the urinary bladder

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand name of some ophthalmic direct-acting miotic drugs include:

• Acetylcholine chloride (Miochol-E)
• Pilocarpine hydrochloride (Isopto Carpine)
• Carbachol (Miostat)