Ophthalmic Pharmacology for the CPOA
The CPOA regularly instills medications, educates patients about their drops, monitors for reactions, and ensures correct drug storage. Understanding the major classes of ophthalmic drugs -- their purposes, mechanisms, expected effects, and potential adverse reactions -- is a core clinical competency. This overview covers the drug classes most frequently encountered in ophthalmic practice.
Diagnostic Agents
Topical Anesthetics
Topical anesthetics (proparacaine 0.5%, tetracaine 0.5%) block sodium channels in corneal nerve fibers, producing rapid-onset surface anesthesia lasting 15-20 minutes. Used before tonometry, foreign body removal, contact lens insertion for fitting, and minor procedures.
Critical point: never dispense topical anesthetics for home use. Patients who self-apply anesthetics prevent pain from guiding healing, leading to chronic epithelial defects, corneal ulcers, and permanent corneal damage.
Mydriatics (Pupil-Dilating Agents)
Mydriatics dilate the pupil without affecting accommodation (or minimally so). They are used for fundus examination:
- Tropicamide (0.5%, 1%): antimuscarinic; onset 20-30 min; duration 4-6 hours; most commonly used
- Phenylephrine (2.5%, 10%): sympathomimetic; dilates without cycloplegia; combined with tropicamide for broader dilation; 10% can raise blood pressure significantly -- caution in cardiac patients
Cycloplegics (Cycloplegic Agents)
Cycloplegics paralyze the ciliary muscle in addition to dilating the pupil. They are used for cycloplegic refraction (especially in children to prevent accommodation from masking hyperopia) and treating uveitis (relieving ciliary spasm and preventing posterior synechiae):
- Cyclopentolate (0.5%, 1%, 2%): onset 30-60 min; duration 24 hours; most common cycloplegic
- Atropine (1%): most potent; duration 7-14 days; used for penalization in amblyopia therapy and severe uveitis
- Scopolamine (Homatropine): intermediate duration
💡 Clinical Tip: Cyclopentolate in young children (especially infants) can cause CNS side effects (irritability, behavioral changes, somnolence) due to systemic absorption through the nasolacrimal duct. Use punctal occlusion and the lowest effective concentration. Report unusual behavioral changes to the physician.
Diagnostic Dyes
- Fluorescein: stains corneal epithelial defects (glows green under cobalt blue light); used in applanation tonometry; also used in fluorescein angiography (IV form)
- Rose bengal / Lissamine green: stains devitalized epithelial cells; used to assess ocular surface integrity in dry eye and corneal disease
Glaucoma Medications
| Drug Class | Mechanism | Example | Side Effects |
|---|---|---|---|
| Prostaglandin analogs | Increases uveoscleral outflow | Latanoprost (Xalatan), bimatoprost (Lumigan) | Iris pigmentation, lash growth, periocular skin darkening; dosed once daily at night |
| Beta-blockers | Decreases aqueous production | Timolol, betaxolol | Bradycardia, bronchospasm (non-selective); caution in asthma, COPD, heart block |
| Alpha-2 agonists | Decreases production, increases uveoscleral outflow | Brimonidine (Alphagan) | Drowsiness; dangerous in infants (apnea, CNS depression) |
| Carbonic anhydrase inhibitors (CAIs) | Decreases aqueous production | Dorzolamide (Trusopt), brinzolamide (Azopt); oral: acetazolamide | Bitter taste; metallic taste; allergy if sulfa allergy (use caution) |
| Rho-kinase inhibitors | Increases trabecular outflow | Netarsudil (Rhopressa) | Conjunctival hyperemia, corneal verticillata |
| Miotics (parasympathomimetics) | Increases trabecular outflow via ciliary muscle contraction | Pilocarpine | Brow ache, dim vision, miosis; used in acute angle-closure |
Anti-Inflammatory Agents
Topical Corticosteroids
Used for uveitis, allergic conjunctivitis, post-surgical inflammation. Examples: prednisolone acetate 1%, difluprednate (Durezol), loteprednol. Risks of prolonged use: elevated IOP (steroid response), posterior subcapsular cataracts, impaired wound healing, increased susceptibility to infection.
NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)
Examples: ketorolac (Acular), bromfenac (Bromday), nepafenac (Nevanac). Used post-operatively (cataract surgery) to prevent CME and for pain. Less IOP risk than steroids.
Antibiotic Drops
Common topical antibiotics: fluoroquinolones (ciprofloxacin, moxifloxacin -- broad-spectrum, preferred for corneal ulcers), tobramycin, erythromycin ointment, trimethoprim/polymyxin (Polytrim). Used for bacterial conjunctivitis, corneal ulcers, pre-operative prophylaxis.
Antiviral Agents
Ganciclovir gel or trifluridine for herpes simplex keratitis. Systemic antivirals (acyclovir, valacyclovir) for herpes zoster ophthalmicus or HSV keratitis.
⚠️ Common Mistake: Topical steroids must never be initiated without physician authorization. Applying steroids to a patient who has a dendritic (herpes simplex) corneal ulcer can cause the infection to dramatically worsen. Never assume anti-inflammatory drops are safe to add without physician direction.
Key Takeaways
- Topical anesthetics must never be prescribed for home use
- Tropicamide (anticholinergic) + phenylephrine (sympathomimetic) is the standard dilation combination
- Cyclopentolate is the most common cycloplegic; atropine is most potent and longest-lasting
- Prostaglandin analogs are first-line glaucoma drops (once nightly); beta-blockers can cause bradycardia and bronchospasm
- Topical steroids can raise IOP and cause cataracts with prolonged use -- physician authorization required
- Never apply steroids to a herpetic corneal ulcer