How Do Antiglaucoma Miotics Work?

Antiglaucoma miotics stimulate the parasympathetic nervous system to make pupils contract (miosis), which increases the outflow 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.

A part of the eye known as the ciliary body produces aqueous humor, which supplies oxygen and nutrients to the lens and cornea and removes waste products. Balancing the inflow and outflow of aqueous humor helps maintain optimum pressure in the eye and it is this pressure that keeps the eyeball roughly in a spherical shape.

Antiglaucoma miotics stimulate the contraction of the ciliary and the sphincter muscles, which make the pupils constrict, increasing the outflow of aqueous humor. Miotics work in two ways:

• Mimic a chemical known as acetylcholine (neurotransmitter) that nerve endings in muscles secrete and stimulate proteins (cholinergic receptors) on eye muscles which respond to acetylcholine and activate muscle contraction.
• Enhance acetylcholine activity by preventing its degradation.

Antiglaucoma miotics are ophthalmic solutions that are topically administered or injected into the eyes. Antiglaucoma miotics are used to reduce intraocular pressure in the following conditions:

• 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 nerve. Reducing intraocular pressure is the primary treatment for glaucoma. Types of glaucoma treated with antiglaucoma 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 results from an injury or other conditions that lead to elevated intraocular pressure, or after cataract surgery.
• To prevent an increase in intraocular pressure after eye surgery.

The use of antiglaucoma miotics has declined since the development of newer antiglaucoma medications with fewer side effects. Side effects of antiglaucoma miotics may include the following:

Ocular side effects:

• Corneal clouding
• Lens opacity
• Pain, burning, and stinging
• Ciliary spasm
• Tearing
• Blurred vision
• Cyst formation in the iris
• Ciliary redness
• Short-sightedness (myopia)
• Eyelid muscle twitching
• Inflammation of the uvea (uveitis), part of the middle layer in the eye
• Retinal detachment (rare)
• Postoperative iris inflammation (iritis) after cataract surgery
• Corneal edema
• Persistent swollen cornea (bullous keratopathy)
• Prolonged miosis from drug
• Raised intraocular pressure
• Eye inflammation
• Ocular hyperemia (dilation of blood vessels in the eye)
• Visual impairment

Systemic side effects:

• Gastrointestinal disturbances such as:
• Salivation
• Nausea and vomiting
• Diarrhea
• Abdominal discomfort or cramps
• Flushing and sweating
• Irregular heartbeat (arrhythmia)
• Slow heartbeat (bradycardia)
• Low blood pressure (hypotension)
• Fainting (syncope)
• Headache
• Tightness in the urinary bladder

The 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 names of some antiglaucoma miotics include:

• Carbachol (Miostat)
• Echothiophate iodide, phospholine iodide