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Glaucoma pharmacology is one of the highest-yield topics on the COA exam within the Pharmacology and Glaucoma domains. The COA must understand not only which drugs are used but how they lower IOP, their dosing schedules, their side effects — local and systemic — and the clinical situations where one drug is preferred or contraindicated over another.
There are currently five classes of topical glaucoma medications: prostaglandin analogs, beta-adrenergic blockers, alpha-2 adrenergic agonists, carbonic anhydrase inhibitors (CAIs), and rho kinase (ROCK) inhibitors. A sixth class — miotics like pilocarpine — was historically important but is now rarely used as first-line therapy. Understanding each class by mechanism, representative drugs, typical IOP reduction, dosing frequency, side effects, and contraindications forms the core of this topic.
The goal of all glaucoma therapy is to lower IOP sufficiently to halt progression of optic nerve damage and visual field loss. Each class achieves this through a different mechanism — either reducing aqueous humor production or increasing its outflow — and no single drug is ideal for all patients.
| Class | Examples | Mechanism | IOP Reduction | Dosing | Key Side Effects |
|---|---|---|---|---|---|
| Prostaglandin analogs | Latanoprost, bimatoprost, travoprost, tafluprost | ↑ Uveoscleral outflow | 25–35% | Once nightly | Hyperemia, lash growth, iris darkening |
| Beta-blockers | Timolol 0.25/0.5%, betaxolol 0.25/0.5% | ↓ Aqueous production | 20–25% | Twice daily | Bradycardia, bronchospasm, fatigue |
| Alpha-2 agonists | Brimonidine 0.1/0.15/0.2%, apraclonidine | ↓ Aqueous production + ↑ uveoscleral outflow | 20–25% | 2–3x daily | Local allergy (10–15%), drowsiness, dry mouth |
| Carbonic anhydrase inhibitors (CAI) | Dorzolamide 2%, brinzolamide 1% (topical); acetazolamide (oral) | ↓ Aqueous production | 15–20% | 2–3x daily (topical) | Bitter taste, stinging (dorzolamide > brinzolamide) |
| ROCK inhibitors | Netarsudil 0.02% (Rhopressa) | ↑ Conventional (trabecular) outflow | ~20% | Once nightly | Conjunctival hyperemia, corneal verticillata |
Prostaglandin analogs are the most potent topical glaucoma agents available and are recommended as first-line monotherapy by most glaucoma guidelines. They reduce IOP by 25–35% by increasing uveoscleral (unconventional) outflow through the ciliary body and supraciliary space, bypassing the trabecular meshwork. Their once-nightly dosing (dosed at bedtime) is a major compliance advantage over agents requiring multiple daily doses.
Beta-blockers were the gold standard first-line agents before prostaglandins became available and remain widely used, especially in combination therapy. They reduce aqueous production by blocking beta-2 adrenergic receptors on the non-pigmented ciliary epithelium. Timolol (non-selective, blocking both beta-1 and beta-2) is the most commonly prescribed. Betaxolol (cardioselective, primarily beta-1) is preferred in patients with mild pulmonary disease as it has less bronchoconstrictor risk, though it is slightly less effective at lowering IOP.
Pulmonary Contraindication
Non-selective beta-blockers (timolol) are contraindicated in asthma, COPD, and reactive airway disease. Beta-2 blockade in bronchial smooth muscle causes bronchoconstriction. Even one drop of timolol can trigger life-threatening bronchospasm in susceptible patients. Always screen for respiratory history before prescribing.
Cardiac Contraindications
Beta-blockers are contraindicated in sinus bradycardia (heart rate below 60), second- or third-degree heart block, cardiogenic shock, and decompensated congestive heart failure. Beta-1 blockade (cardiac) slows heart rate and reduces contractility. Timolol eyedrops can reduce resting heart rate by 6–8 bpm with systemic absorption.
Masking of Hypoglycemia
Beta-blockers mask the tachycardia that signals hypoglycemia in diabetic patients on insulin. Alert prescribers when adding beta-blocker drops to insulin-dependent diabetics.
Short-Term Drift
Beta-blockers exhibit "short-term drift" — their IOP-lowering effect diminishes over the first few weeks of use as the ciliary body upregulates receptors. The long-term effect stabilizes at a lower level than initial response, which is why they are sometimes replaced by prostaglandins as first-line therapy.
Brimonidine tartrate (Alphagan P) is the primary alpha-2 agonist in current use. It lowers IOP through two mechanisms: reducing aqueous production (by inhibiting adenylyl cyclase in ciliary epithelium) and increasing uveoscleral outflow. This dual mechanism makes it particularly effective as an additive agent. The Purite-preserved formulation (Alphagan P 0.1% and 0.15%) has a lower rate of local allergy than the original benzalkonium chloride formulations.
Apraclonidine (Iopidine 0.5%, 1%) is a less selective alpha-2 agonist used primarily as short-term adjunctive therapy before and after anterior segment laser procedures to blunt the post-laser IOP spike. It is not suitable for chronic use due to a very high rate of local allergic reactions (tachyphylaxis, follicular conjunctivitis).
Brimonidine is absolutely contraindicated in children under 2 years of age and used with extreme caution in older children. It crosses the blood-brain barrier freely in infants (whose BBB is less mature), causing profound CNS depression: apnea, hypotension, bradycardia, hypothermia, and coma. Multiple reported cases of infant apnea requiring hospitalization. Never instill brimonidine in pediatric patients without explicit physician review of the patient's age.
CAIs lower IOP by blocking carbonic anhydrase II in the non-pigmented ciliary epithelium, reducing bicarbonate secretion and thereby reducing aqueous humor production. Topical agents (dorzolamide 2% TID/BID, brinzolamide 1% TID) are used as additive therapy when prostaglandins or beta-blockers alone are insufficient.
Oral acetazolamide (Diamox) provides much more powerful IOP reduction (25–30%) and is used for acute angle-closure emergencies or when maximum IOP reduction is needed preoperatively. However, its systemic side effects (metabolic acidosis, hypokalemia, renal calculi, paresthesias, malaise, altered taste) limit long-term use.
Netarsudil (Rhopressa 0.02%) is the first and only ROCK inhibitor approved for glaucoma. It works by a fundamentally different mechanism from all other classes: it increases conventional trabecular outflow — the primary physiological drainage route — by relaxing trabecular meshwork cells and increasing the permeability of Schlemm's canal. It also reduces episcleral venous pressure and aqueous production as secondary effects.
Netarsudil is dosed once nightly and approved as monotherapy or adjunct. It is also available in a fixed combination with latanoprost as Rocklatan, which provides additive IOP reduction from both the trabecular and uveoscleral outflow pathways.
Fixed combination drops simplify regimens for patients on multiple agents, improving compliance by reducing the number of instillations per day. When two drops must be used separately, patients should wait at least 5 minutes between instillations to prevent the second drop from washing out the first.
| Brand Name | Components | Dosing |
|---|---|---|
| Cosopt | Dorzolamide 2% + timolol 0.5% | Twice daily |
| Combigan | Brimonidine 0.2% + timolol 0.5% | Twice daily |
| Simbrinza | Brinzolamide 1% + brimonidine 0.2% | Three times daily |
| Rocklatan | Netarsudil 0.02% + latanoprost 0.005% | Once nightly |
| DuoTrav | Travoprost 0.004% + timolol 0.5% | Once daily (morning) |
Medication non-compliance is one of the leading causes of glaucoma progression despite adequate medical therapy. Research shows that a significant proportion of glaucoma patients (estimates range from 30–80%) are non-adherent to their prescribed regimens. The COA plays a critical role in assessing and supporting compliance through patient education.
Ask open-ended compliance questions
Rather than “Are you using your drops?” (which invites a yes answer), ask “How often do you miss a dose?” or “Walk me through how you use your drops each day.” This reveals actual habits without creating a defensive response.
Check for residual medication in bottles
Ask patients to bring their current bottles to appointments. Count remaining doses or note the fill date and refill date on the label. Bottles that should be nearly empty but are still mostly full indicate missed doses.
Reinforce the silent nature of glaucoma
Glaucoma causes no pain and vision loss is typically not noticed until late-stage disease. Patients may not feel motivated to treat a condition they cannot perceive. Explain that the drops protect the optic nerve from silent, irreversible damage and that vision loss cannot be reversed once it occurs.
Opterio covers all five glaucoma drug classes with adaptive COA exam questions, AI-powered explanations, and spaced repetition for long-term retention.
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The five main classes are: (1) Prostaglandin analogs (latanoprost, bimatoprost, travoprost, tafluprost) — increase uveoscleral outflow; most effective IOP reduction of 25–35%; dosed once nightly. (2) Beta-blockers (timolol, betaxolol) — reduce aqueous humor production; 20–25% IOP reduction; dosed twice daily. (3) Alpha-2 adrenergic agonists (brimonidine, apraclonidine) — reduce aqueous production and increase uveoscleral outflow; 20–25% reduction; dosed 2–3 times daily. (4) Carbonic anhydrase inhibitors (dorzolamide, brinzolamide topically; acetazolamide orally) — reduce aqueous production by blocking carbonic anhydrase in ciliary epithelium; 15–20% reduction. (5) Rho kinase (ROCK) inhibitors (netarsudil) — increase conventional trabecular outflow; ~20% reduction; dosed once nightly.
Prostaglandin analogs are the most effective first-line glaucoma agents but have several characteristic local side effects: (1) Conjunctival hyperemia (redness) — common, especially with bimatoprost; may improve over time. (2) Eyelash changes — increased length, thickness, pigmentation, and number of lashes (hypertrichosis). (3) Iris pigmentation changes — permanent darkening of the iris due to increased melanin synthesis in iris melanocytes, most evident in hazel/mixed irides. (4) Periorbital fat atrophy and deepening of the upper lid sulcus with chronic use. (5) Prostaglandin-associated periorbitopathy (PAP) — a newer recognized syndrome of orbital fat loss, ptosis, and enophthalmos. (6) Reactivation of uveitis and herpetic keratitis has been reported. Systemic absorption is minimal, making them safe for most patients with cardiac or pulmonary disease.
Beta-blockers like timolol 0.5% block both beta-1 (cardiac) and beta-2 (pulmonary) adrenergic receptors. Beta-2 receptors in bronchial smooth muscle normally mediate bronchodilation. Blocking these receptors can cause bronchoconstriction, potentially triggering severe bronchospasm in patients with reactive airway disease such as asthma or COPD. Even "cardioselective" ophthalmic beta-blockers like betaxolol (which preferentially blocks beta-1 receptors) carry some risk. Systemic absorption via the nasolacrimal duct is sufficient to cause clinically significant bronchoconstriction. Beta-blockers are also contraindicated in sinus bradycardia, heart block greater than first degree, cardiogenic shock, and decompensated heart failure.
Brimonidine (Alphagan) is a highly selective alpha-2 adrenergic agonist that reduces aqueous production and mildly increases uveoscleral outflow. Its alpha-2 selectivity (1000:1 alpha-2 to alpha-1 ratio) makes it much less likely to cause the systemic hypertension and cardiovascular effects of less selective alpha agonists. It is also neuroprotective in animal models. However, brimonidine readily crosses the blood-brain barrier in infants and young children (under age 2), causing potentially life-threatening central nervous system depression including apnea, hypotension, bradycardia, and coma. Brimonidine is therefore absolutely contraindicated in children under 2 years and used with extreme caution in older children. Additionally, about 10–15% of adults develop a local allergic reaction (follicular conjunctivitis) to brimonidine over time, requiring drug discontinuation.
Rho kinase (ROCK) inhibitors like netarsudil (Rhopressa, 0.02%) represent the newest class of glaucoma medications. Unlike all other glaucoma drugs that either reduce aqueous production or increase uveoscleral (unconventional) outflow, ROCK inhibitors primarily increase conventional trabecular outflow through the trabecular meshwork and Schlemm's canal — the primary physiologic drainage pathway. They achieve this by relaxing trabecular meshwork cells (which are tonically contracted by the Rho kinase pathway), increasing their porosity. Netarsudil also reduces aqueous production and episcleral venous pressure. The main side effect is conjunctival hyperemia (very common, affecting most patients), corneal verticillata (whorled corneal deposits), and conjunctival hemorrhage. It is dosed once nightly and can be combined with latanoprost (Rocklatan). ROCK inhibitors are especially effective in patients with low baseline IOP as they show IOP-independent pressure effects.