Introduction
Mydriatics and miotics are important ophthalmic drugs used during eye examination and in treating eye diseases. Mydriatics dilate the pupil, while miotics constrict the pupil. These drugs act on specific muscles of the iris and are widely used in glaucoma, uveitis, refraction testing and ocular emergencies.
What Are Miotics?
Miotics are drugs that produce pupil constriction. They mainly stimulate the parasympathetic system and contract the sphincter pupillae muscle. Miotics improve fluid drainage in glaucoma and help in conditions where increased accommodation is required.
1. Pilocarpine
Pilocarpine is a direct-acting parasympathomimetic drug that stimulates muscarinic receptors. It does not affect nicotinic receptors.
Uses
- Angle-closure glaucoma
- Emergency reversal of drug-induced mydriasis
- Accommodative strabismus
- After cataract extraction (selected cases)
Warnings and Adverse Effects
- Systemic absorption may cause sweating, nausea, vomiting and diarrhoea.
- Risk of retinal detachment in predisposed patients.
- Visual blurring, accommodative spasm and poor night vision.
Dosage
Applied 1–2 drops for emergency miosis; otherwise used 2–4 times daily.
2. Carbachol
Carbachol is a cholinergic drug with both muscarinic and nicotinic action. It is used when pilocarpine is not effective or not tolerated.
Uses
- Glaucoma treatment (intra-ocular pressure reduction)
Adverse Effects
- Ciliary spasm, headache, lacrimation
- Possible systemic cholinergic symptoms (salivation, vomiting, cramps)
Dosage
Used three to four times daily as eye drops.
3. Phospholine Iodide
A long-acting cholinesterase inhibitor that increases ACh at eye tissues, causing strong miosis.
Uses
- Chronic open-angle glaucoma
- Sub-acute or chronic angle-closure glaucoma
Adverse Effects
- Lid twitching, irritation, brow ache
- Iritis, iris cysts
- Lens opacities with prolonged use
4. Physostigmine
A reversible anticholinesterase used occasionally in glaucoma and diagnostic procedures.
Adverse Effects
- Twitching, irritation, allergic response
- Pigmentation changes of eyelid skin (rare)
What Are Mydriatics?
Mydriatics are drugs that dilate the pupil. Some also paralyse the ciliary muscle, a condition known as cycloplegia. These drugs help in fundoscopy, refraction testing and ocular diagnosis.
1. Phenylephrine
Phenylephrine is a direct-acting alpha-agonist. It dilates the pupil without cycloplegia.
Uses
- Dilation for fundus examination
- Diagnostic test for Horner’s syndrome
- Provocative test for angle-closure glaucoma
Contraindications
- Angle-closure glaucoma
- Hypertension (risk of systemic absorption)
- Infants (10% solution)
Adverse Effects
- Stinging, rebound congestion
- Tachycardia, hypertension
- Rare arrhythmias in elderly patients
Dosage
1–2 drops topically; maximum effect in 15–60 minutes; pupil returns to normal within 4–6 hours.
Clinical Difference Between Miotics and Mydriatics
| Feature | Miotics | Mydriatics |
|---|---|---|
| Effect on Pupil | Constrict | Dilate |
| Main Use | Glaucoma treatment | Eye examination and diagnosis |
| Main Drug Classes | Cholinergic agonists | Alpha agonists, anticholinergics |
| Important Side Effects | Blurred vision, headache, retinal risks | Hypertension, tachycardia, stinging |
Precautions for Use
- Avoid driving immediately after using strong miotics or mydriatics.
- Store ophthalmic solutions properly to prevent degradation.
- Patients with asthma, cardiac disease or hypertension should be closely monitored.
- Avoid over-usage to reduce systemic side effects.
Detailed Notes:
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