How Do Cholinesterase Inhibitor Miotics Work?

Cholinesterase inhibitor miotics are medications that make the pupils constrict by inhibiting the activity of an enzyme known as cholinesterase. Pupil constriction (miosis) improves the outflow of aqueous humor and helps reduce 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.

Cholinesterase is an enzyme that breaks down a chemical (neurotransmitter) known as acetylcholine that nerve endings in muscles secrete to stimulate muscle contraction. Cholinesterase inhibitors work indirectly to maintain muscle contraction by blocking cholinesterase activity and slowing down the breakdown of acetylcholine.

Cholinesterase inhibitors 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 helps maintain optimum pressure in the eye and the eye’s spherical shape.

Cholinesterase inhibitor miotics are ophthalmic solutions administered topically in the eye to treat glaucoma, a progressive disease that damages the optic nerve. Reducing intraocular pressure is the primary treatment for glaucoma because elevated intraocular pressure damages the nerve further.

Types of glaucoma treated with cholinesterase inhibitor miotics include:

• Open-angle glaucoma: The most common type of glaucoma, in which the drainage angle through which the aqueous humor drains remains open, but the drainage channels are partially blocked.
• Secondary glaucoma: Secondary glaucoma can occur following cataract surgery, from an eye injury, or other conditions that lead to elevated intraocular pressure.

Side effects of Cholinesterase inhibitor miotics may include:

Ocular side effects:

• Burning and stinging
• Tearing (lacrimation)
• Iris cyst formation
• Blurred vision
• Ciliary redness
• Increased intraocular pressure
• Short-sightedness (myopia)
• Persistent miosis
• Eyelid muscle twitching
• Inflammation of the uvea (uveitis), part of the middle layer in the eye
• Lens opacities
• Retinal detachment

Systemic side effects:

• Slow heartbeat (bradycardia)
• Low blood pressure (hypotension)
• Nausea and vomiting
• Diarrhea

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 a commonly used cholinesterase inhibitor miotic drug is:

• Echothiophate iodide (Phospholine iodide)