MIOTICS, MYDRIATICS AND cyclopiegics PDF

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Access a comprehensive Miotics, Mydriatics, and Cycloplegics PDF. These notes detail important classes of ophthalmic drugs that affect the autonomic control of pupillary size and accommodation. Understanding their mechanisms of action, therapeutic uses in eye examinations and treatment of conditions like glaucoma, and potential side effects is crucial for students of pharmacology, ophthalmology, optometry, and medicine. You can download this "Miotics, Mydriatics, and Cycloplegics PDF" for free for offline study or view it directly online. Slides By DuloMix provides these specialized educational materials to support your learning in ocular pharmacology.

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• Specialized Ocular Pharmacology: Focuses on drugs acting on the eye's autonomic innervation, a key area in ophthalmology.
• Clear Explanations of Mechanisms: Details how these drugs interact with cholinergic and adrenergic receptors in the eye.
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Miotics, Mydriatics, and Cycloplegics: Pharmacology of Ocular Autonomic Drugs

Miotics, mydriatics, and cycloplegics are classes of ophthalmic drugs that primarily act on the autonomic nervous system innervation of the eye. They are used extensively in ophthalmology for both diagnostic and therapeutic purposes, influencing pupillary size and the eye's ability to accommodate (focus on near objects). Understanding their mechanisms requires a grasp of the autonomic control of the iris and ciliary muscle.

Autonomic Innervation of the Eye

• Iris Muscles:
  • Sphincter Pupillae (Circular Muscle): Innervated by parasympathetic fibers (cholinergic, muscarinic M₃ receptors). Contraction causes pupillary constriction (miosis).
  • Dilator Pupillae (Radial Muscle): Innervated by sympathetic fibers (adrenergic, α₁ receptors). Contraction causes pupillary dilation (mydriasis).
• Ciliary Muscle:
  • Primarily innervated by parasympathetic fibers (cholinergic, muscarinic M₃ receptors). Contraction leads to relaxation of suspensory ligaments, allowing the lens to become more convex for near vision (accommodation).
  • Minor sympathetic innervation (β₂ receptors) may cause slight relaxation of the ciliary muscle.

I. Miotics (Pupil Constrictors)

Miotics are drugs that cause constriction of the pupil. They primarily achieve this by stimulating the parasympathetic nervous system or blocking the sympathetic nervous system's effect on the iris, although parasympathomimetics are the main class.

A. Mechanism of Action

• Cholinergic Agonists (Parasympathomimetics):
  • Direct-acting: Bind to and activate muscarinic receptors (M₃) on the sphincter pupillae muscle, causing it to contract, leading to miosis. They also contract the ciliary muscle, facilitating accommodation and increasing aqueous humor outflow through the trabecular meshwork (useful in glaucoma).
    • Examples: Pilocarpine, Carbachol, Acetylcholine (intraocular).
  • Indirect-acting (Anticholinesterases): Inhibit the enzyme acetylcholinesterase, preventing the breakdown of acetylcholine (ACh) at the neuromuscular junction. This leads to increased ACh concentration, enhancing parasympathetic effects.
    • Reversible: Physostigmine, Neostigmine, Echothiophate (long-acting, organophosphate - rarely used now due to side effects).
    • Irreversible: Organophosphates (e.g., some insecticides) - not used therapeutically for miosis due to toxicity.
• Alpha-adrenergic Antagonists (Sympatholytics): (Less common for primary miotic effect)
  • Drugs like Dapiprazole can block α₁ receptors on the dilator pupillae muscle, leading to passive miosis or reversal of mydriasis caused by alpha-agonists.

B. Therapeutic Uses

• Glaucoma: Particularly angle-closure glaucoma (pilocarpine can pull the peripheral iris away from the trabecular meshwork, opening the angle) and open-angle glaucoma (by increasing trabecular outflow of aqueous humor).
• Reversal of Mydriasis: After diagnostic eye exams or surgical procedures.
• Management of Accommodative Esotropia.
• Diagnosis: Pilocarpine test for Adie's tonic pupil.

C. Adverse Effects

• Blurred vision (due to miosis and induced myopia from ciliary spasm), brow ache, headache.
• Systemic effects (if absorbed): Salivation, lacrimation, urination, defecation, GI upset, bronchospasm (SLUDGE syndrome with anticholinesterases).
• Risk of retinal detachment (rare, with strong miotics).

II. Mydriatics (Pupil Dilators)

Mydriatics are drugs that cause dilation of the pupil. They work by stimulating the sympathetic nervous system or blocking the parasympathetic nervous system's effect on the iris.

A. Mechanism of Action

• Adrenergic Agonists (Sympathomimetics):
  • Stimulate α₁-adrenergic receptors on the dilator pupillae muscle, causing it to contract, leading to mydriasis.
    • Examples: Phenylephrine.
    • These drugs typically do not cause significant cycloplegia (paralysis of accommodation).
• Cholinergic Antagonists (Parasympatholytics / Antimuscarinics):
  • Block muscarinic receptors on the sphincter pupillae muscle, preventing acetylcholine from causing constriction. This allows the sympathetically innervated dilator muscle to act unopposed, leading to mydriasis.
  • These drugs also block muscarinic receptors on the ciliary muscle, causing cycloplegia (see below). Therefore, most antimuscarinics are both mydriatics and cycloplegics.
    • Examples: Atropine, Homatropine, Cyclopentolate, Tropicamide.

B. Therapeutic Uses

• Diagnostic Eye Examinations: To allow better visualization of the retina and other posterior segment structures (fundoscopy).
• Prevention of Synechiae (adhesions): In uveitis or iritis, by keeping the iris mobile.
• Breaking existing synechiae.
• Refraction: Cycloplegic mydriatics are used to paralyze accommodation for accurate refractive error measurement, especially in children.

C. Adverse Effects

• Local: Stinging/burning on instillation, blurred vision, photophobia (due to dilated pupil). Increased intraocular pressure (IOP) in patients with narrow angles or angle-closure glaucoma (contraindicated or used with extreme caution). Allergic reactions.
• Systemic (especially with antimuscarinics): Dry mouth, tachycardia, flushing, fever, constipation, urinary retention, CNS effects (confusion, hallucinations, especially in children and elderly with atropine-like drugs). Phenylephrine can cause hypertension, palpitations.

III. Cycloplegics (Paralyzers of Accommodation)

Cycloplegics are drugs that paralyze the ciliary muscle, resulting in a loss of accommodation (ability to focus on near objects). Most cycloplegics are also mydriatics because they are antimuscarinic agents.

A. Mechanism of Action

• Cholinergic Antagonists (Parasympatholytics / Antimuscarinics):
  • Block muscarinic receptors (M₃) on the ciliary muscle, preventing its contraction. This keeps the suspensory ligaments taut and the lens relatively flat, impairing near vision.
  • Examples: Atropine (long-acting), Homatropine (intermediate), Cyclopentolate (commonly used for refraction), Tropicamide (short-acting, primarily mydriatic with weaker cycloplegic effect at lower doses).

B. Therapeutic Uses

• Refraction: To obtain an accurate measurement of refractive error by preventing the patient from accommodating, especially important in children who have strong accommodative power.
• Treatment of Uveitis/Iritis: To relieve pain from ciliary spasm and prevent posterior synechiae formation by immobilizing the iris and ciliary body.

C. Adverse Effects

• Loss of accommodation (blurred near vision), photophobia (due to associated mydriasis).
• Same local and systemic side effects as antimuscarinic mydriatics (see above), as these drugs typically possess both properties. Risk of precipitating angle-closure glaucoma.

Key Considerations

• Onset and Duration of Action: Varies significantly among drugs (e.g., Tropicamide has a rapid onset and shorter duration, making it ideal for routine fundoscopy; Atropine has a very long duration of action).
• Patient Factors: Age (children have stronger accommodation), iris pigmentation (darker irises may require higher concentrations or longer time for effect), and pre-existing conditions (e.g., risk of angle closure glaucoma) influence drug choice and dosage.
• Proper Instillation Technique: To maximize ocular absorption and minimize systemic absorption (e.g., punctal occlusion).

The use of miotics, mydriatics, and cycloplegics is integral to ophthalmic practice. A thorough understanding of their pharmacology allows for their safe and effective application in diagnosing and treating various eye conditions. These notes provide a foundational overview of these important drug classes.

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