Glaucoma
Clinical Snapshot
Glaucoma is a group of optic neuropathies in which progressive damage to the optic nerve leads to irreversible peripheral visual field loss, with characteristic thinning of the retinal nerve fibre layer, cupping of the optic disc, and field loss that typically precedes any loss of central visual acuity.[1] The distinction that determines everything about management is whether the anterior chamber angle — the space where the iris meets the cornea, through which aqueous humor drains — is open or narrowed/closed. Open-angle glaucoma is the most common form: usually bilateral, chronic, and silent, with patients typically asymptomatic until advanced field loss has already occurred. Angle-closure glaucoma is fundamentally different: when the angle closes acutely, aqueous outflow is suddenly obstructed, intraocular pressure (IOP) rises rapidly, and the result is a painful, symptomatic, true ophthalmic emergency requiring an entirely different, urgent treatment sequence from routine open-angle management.[2] Elevated IOP is the only modifiable risk factor for glaucoma, and every proven treatment — medical, laser, or surgical — works by lowering it.
Recognize the Condition
Open-angle glaucoma
The great majority of patients with open-angle glaucoma are completely asymptomatic until the disease is advanced. There is no eye pain and no redness. Vision loss begins in the peripheral field and often goes unnoticed for years, since central visual acuity is preserved until late in the disease. When patients do report symptoms, they are subtle — difficulty with night driving, bumping into objects or furniture, or missing words at the edge of the visual field while reading. Because of this silent course, the diagnosis is made almost entirely on examination findings, not on presenting symptoms.
Angle-closure glaucoma
Angle-closure glaucoma can present acutely, or can be just as silent as open-angle disease.
How each type of glaucoma presents
Acute angle-closure crisis
Severe, usually unilateral eye pain; a red eye with a hazy or cloudy cornea; markedly blurred vision; halos around lights; headache; and nausea or vomiting. Examination reveals a fixed, mid-dilated pupil and a firm-feeling globe. This is a true ophthalmic emergency — see Red Flags & Refer.
Chronic angle-closure glaucoma
The angle narrows gradually and progressively without ever triggering a painful crisis. Presentation is as silent as open-angle glaucoma and is typically discovered only on gonioscopic examination or once optic nerve or field damage is already present.
Subacute (intermittent) angle-closure
Repeated, self-limited episodes of mild eye ache, blurred vision, and halos that resolve spontaneously as the pupil relaxes. A history of these episodes is an important clue and a strong indication for prophylactic laser iridotomy before a true acute crisis occurs.
Secondary glaucoma
Elevated IOP as a consequence of another ocular or systemic process — for example neovascular angle-closure glaucoma from proliferative diabetic retinopathy or central retinal vein occlusion, pigment dispersion syndrome, pseudoexfoliation syndrome, trauma, prior intraocular surgery or inflammation, or corticosteroid use. Presentation follows the underlying open-angle or angle-closure pattern.
Congenital glaucoma
Rare; presents in infancy with tearing, photophobia, blepharospasm, and a cloudy, enlarged cornea (buphthalmos). Requires urgent pediatric ophthalmology referral.
Risk Factors
Open-angle glaucoma
- Elevated intraocular pressure — the only modifiable risk factor.
- Advanced age.
- Positive family history of glaucoma.
- Myopia (nearsightedness).
- Vascular disease, including migraine, hypertension, and nocturnal hypotension.
- Type 2 diabetes mellitus.
- Blunt or penetrating ocular trauma.
- Previous intraocular surgery or intraocular inflammation.
- Corticosteroid use by any route — inhaled, intranasal, ophthalmic, topical, or systemic.
- Pseudoexfoliation syndrome.
- Pigment dispersion syndrome.
- Long-term oral contraceptive use (over 3 years) has been associated with primary open-angle glaucoma.
Angle-closure glaucoma
- Female sex.
- Advanced age.
- Hyperopia (farsightedness), associated with a structurally shallow anterior chamber and a narrow angle.
- Positive family history of angle-closure glaucoma.
- A previous acute angle-closure attack in the contralateral eye is a strong risk factor for the fellow eye.
- East Asian or Inuit ancestry, both associated with anatomically shallower anterior chambers.
- Proliferative diabetic retinopathy and central retinal vein occlusion, which can cause neovascular angle-closure glaucoma.
Medication-induced risk — a genuine medication-review point
- Systemic drugs with antimuscarinic (anticholinergic) activity — including many antidepressants, antihistamines, antispasmodics, and decongestants — can rarely precipitate acute angle-closure glaucoma in a predisposed patient, such as an older, significantly hyperopic patient with a positive family history who has not yet had a prophylactic iridotomy.
- Topiramate has been specifically associated with acute, bilateral, secondary angle-closure glaucoma, typically within the first weeks of starting the drug, through a distinct mechanism (ciliary body swelling and anterior lens-iris displacement) rather than classic pupillary block.[3]
- Bupropion has also been associated with an increased risk of angle-closure glaucoma.[4]
- Corticosteroid use by any route can precipitate or worsen open-angle glaucoma and is itself a reason for periodic IOP monitoring in a patient with additional risk factors.
Red Flags & Refer
Acute angle-closure glaucoma is a true ophthalmic emergency — any patient with this presentation needs immediate emergency IOP-lowering treatment and same-day ophthalmology involvement, not a routine referral.
- Severe eye pain, often accompanied by headache, nausea, and vomiting.
- Halos around lights, especially noticed at night.
- A red eye with a hazy or cloudy-appearing cornea.
- A fixed, mid-dilated pupil that does not react normally to light.
- Sudden, marked decrease in vision.
- A firm-feeling globe on gentle palpation, reflecting significantly elevated intraocular pressure.
- New eye pain or redness in a patient recently started on a systemic anticholinergic, topiramate, or bupropion — assess urgently for drug-induced acute angle closure and hold the suspected drug pending ophthalmology assessment.[3]
- Any sudden vision loss, regardless of presumed cause, warrants same-day ophthalmic assessment.
- Progressive visual field loss or optic disc change despite treatment, or IOP persistently above the individualized target, needs referral back to ophthalmology for treatment escalation.
Assessment & Diagnosis
Distinguishing the types of glaucoma on presentation
| Parameter | Open-angle glaucoma | Acute angle-closure glaucoma | Chronic angle-closure glaucoma |
|---|---|---|---|
| Onset | Gradual, silent | Sudden | Gradual, silent (like open-angle) |
| Eye pain | Absent | Severe | Absent, or mild and self-limited if subacute |
| Vision | Normal until advanced (peripheral field loss first) | Markedly blurred, halos around lights | Normal until advanced, like open-angle |
| Conjunctiva/cornea | Normal | Red eye, hazy or cloudy cornea | Normal |
| Pupil | Normal, reactive | Fixed, mid-dilated | Normal, reactive |
| Associated symptoms | None | Headache, nausea, vomiting | None |
| Anterior chamber angle (gonioscopy) | Open | Closed | Narrow, progressively or intermittently closing |
| Urgency | Routine, chronic management | Immediate emergency treatment | Routine referral for prophylactic laser iridotomy |
History
- Nature of any ocular disturbances — loss of peripheral vision, scotoma, halos around lights, decreased visual acuity.
- Impact on reading, daily activities, driving or night driving; falling; bumping into objects.
- Quality of any pain — deep orbital, brow, or headache.
- Associated systemic symptoms — abdominal pain, nausea and vomiting.
- Full medication history, specifically asking about corticosteroids (any route), drugs with antimuscarinic activity, topiramate, bupropion, and long-term oral contraceptive use (see Risk Factors).
Physical examination
- Eye examination — visual field by confrontation, optic disc cupping, and IOP measurement.
- Gonioscopy to examine the anterior chamber angle directly and classify open versus narrow/closed.
Elevated IOP alone is neither a sensitive nor a specific screening test for glaucoma — a meaningful proportion of people with glaucoma have IOP within the statistically normal range, and most people with an elevated IOP reading never go on to develop glaucoma, though their risk is increased. Systematic population screening is therefore not recommended, but a dedicated ophthalmic examination including IOP should be considered for patients with a personal history (glaucoma in the contralateral eye) or family history of glaucoma, and for patients on regular corticosteroid therapy (oral, inhaled, intranasal, or topical) who have additional risk factors.[1]
Investigations
- Comprehensive eye examination by an ophthalmologist or optometrist.
- Automated perimetry (formal visual field testing).
- Optic disc photography.
- Central corneal thickness measurement.
- Optic disc and retinal nerve fibre layer imaging (e.g. OCT).
Setting an individualized target IOP
Target IOP is set for each patient based on the extent of existing glaucomatous damage (disc cupping, peripheral field loss), the IOP range believed to have been associated with that damage, and the burden of therapy needed to reach the desired pressure. The target is adjusted further downward if progressive optic disc or visual field damage occurs despite reaching the original target — reaching a numeric target IOP is not itself proof that treatment is adequate if the disc or field is still worsening.
Treatment Targets
- Prevent, halt, or slow progressive visual field loss.
- Preserve the structure and function of the optic nerve.
- Lower intraocular pressure to an individualized target range — the only proven, modifiable lever in every form of glaucoma.
- In acute angle-closure glaucoma specifically: rapidly eliminate pain and urgently lower IOP to prevent permanent optic nerve damage and vision loss.
- Improve or maintain quality of life and functional vision, including night driving and reading.
Choose Initial Treatment
In a patient with a classic acute angle-closure presentation (severe eye pain, red eye, halos, fixed mid-dilated pupil, markedly elevated IOP), begin emergency IOP-lowering treatment immediately rather than delaying for further confirmatory testing.
Start combined topical therapy at once: one drop each of a topical beta-blocker (timolol 0.5 percent), a topical alpha-2 agonist (apraclonidine 1 percent or brimonidine), and a topical carbonic anhydrase inhibitor (dorzolamide or brinzolamide), together with an oral or intravenous carbonic anhydrase inhibitor — acetazolamide 500 mg once, unless contraindicated.[5]
Position the patient supine to shift the lens posteriorly and relieve pupillary block, treat pain and nausea with analgesics and antiemetics, and add a topical corticosteroid to reduce anterior segment inflammation.
Do not give pilocarpine as the very first drug — at very high IOP the iris sphincter is ischemic and will not respond. Add pilocarpine 1 to 2 percent only once IOP has begun to fall with the agents above, typically after the first hour.
If IOP remains dangerously elevated after about an hour of combined topical and systemic therapy, add intravenous mannitol.
Definitive treatment is laser peripheral iridotomy (or surgical iridectomy if laser is not feasible) as soon as the cornea has cleared enough to proceed, plus prophylactic laser iridotomy in the fellow eye, which carries a meaningfully increased risk of a future attack of its own.[2]
1st line a topical prostaglandin analogue — latanoprost, travoprost, bimatoprost, or tafluprost — one drop once daily in the evening. Any of these may be used first-line given comparable effectiveness and a favourable safety profile.[1]
2nd line — use when a prostaglandin analogue is not tolerated, contraindicated, or target IOP is not yet reached add or substitute a topical beta-blocker (if no asthma, COPD, or bradycardia/heart block), a topical alpha-2 agonist, or a topical carbonic anhydrase inhibitor.
When two or more agent classes are needed long-term, prefer a fixed-combination product over separate bottles to improve adherence and reduce preservative exposure and washout between drops.[6]
Escalate to laser trabeculoplasty when medication is not tolerated, when adherence is a genuine ongoing concern (cost, technique, memory), or earlier by patient preference or disease characteristics (e.g. pseudoexfoliation, pigment dispersion syndrome).
Escalate further to incisional surgery (trabeculectomy or another filtration procedure, or a drainage device) when maximally tolerated medical therapy and laser treatment together are still insufficient to reach target IOP or halt progression.
Non-Pharmacologic Treatment
Correct eye drop administration technique
Topical glaucoma medications are highly concentrated to achieve adequate penetration into the eye, and a meaningful fraction of every dose drains through the nasolacrimal duct into the nose and throat, where it is absorbed directly into the systemic circulation, bypassing first-pass hepatic metabolism. This is the mechanism behind the systemic beta-blockade risk from topical timolol and betaxolol (see Red Flags and Drug Tables), and is a genuine, teachable adherence and safety point for every patient started on any topical glaucoma medication.
- Nasolacrimal occlusion: press gently on the inner corner of the eye, over the tear duct, for 2 to 5 minutes after instilling each drop, or simply close the eyelids gently for the same duration. Both meaningfully reduce systemic absorption.[7]
- Wait at least 5 minutes between two different eye drops, to avoid washing out the first medication before it has been absorbed.
- Remove soft contact lenses before instilling drops and wait at least 15 minutes before reinserting them — the benzalkonium chloride preservative in many formulations can be absorbed by, and discolour, soft lenses.
- Blot away any excess solution that runs onto the eyelid skin, particularly with a prostaglandin analogue, to reduce the risk of periocular skin darkening.
- Do not let the dropper tip touch the eye or any other surface, to avoid contaminating the bottle and causing a serious eye infection.
Cannabis is not an appropriate glaucoma treatment
Laser and surgical escalation
Lifestyle modification has not been shown to alter the course of glaucoma, though regular aerobic exercise can modestly lower IOP in some patients — a reasonable general health recommendation, but never a substitute for IOP-lowering treatment. When medical therapy is insufficient, not tolerated, or adherence is a genuine ongoing concern, laser or surgical treatment is used to lower IOP directly.
Laser and surgical options, by indication
Laser trabeculoplasty (argon or selective)
Applies laser energy to the trabecular meshwork to improve drainage. Effect is time-limited (years, not permanent). A reasonable first-line option — not only a last resort — for patients who are elderly, cannot reliably adhere to a drop regimen, or who have primary open-angle glaucoma, pseudoexfoliation syndrome, or pigment dispersion syndrome.
Laser peripheral iridotomy
Creates a small hole in the iris with a YAG laser to let aqueous flow directly from the posterior to the anterior chamber, bypassing pupillary block. A simple office procedure with a long-term effect. The definitive treatment for both acute and chronic angle-closure glaucoma, and used prophylactically in the fellow eye after an acute attack.
Laser iridoplasty
An alternative when iridotomy cannot be performed immediately (e.g. corneal edema obscuring the view), used to mechanically pull the peripheral iris away from the angle.
Filtration surgery (trabeculectomy and related procedures)
Creates a new drainage channel from the anterior chamber to a subconjunctival space. Reserved for open-angle glaucoma refractory to medical and laser treatment.
Surgical iridectomy
Used in the affected eye, and prophylactically in the fellow eye, when angle-closure glaucoma is refractory to laser iridotomy.
Drainage tube (glaucoma drainage device)
A small tube drains aqueous to an implanted plate beneath the conjunctiva. Reserved for any form of glaucoma where other surgical procedures have not succeeded.
Cyclophotocoagulation
Laser ablation of the ciliary body to reduce aqueous production. Reserved for advanced, refractory glaucoma where other options are limited.
Special Populations
Pregnancy
Breastfeeding
Brimonidine should not be used by a breastfeeding parent of a young infant — it is absorbed systemically and can cause apnea and CNS depression in a nursing infant, mirroring the reason it is contraindicated in young children. Timolol passes into breast milk; weigh the importance of the drug against potential infant exposure. Prostaglandin analogue data in lactation are limited; use with caution.
Pediatrics
Brimonidine is contraindicated in infants and young children (generally under 2 years of age) because of CNS depression, apnea, bradycardia, hypotension, and hypothermia risk from systemic absorption relative to body weight, and should be used with caution in older young children for the same reason. Congenital glaucoma requires urgent pediatric ophthalmology referral rather than adult-pattern management. Most other topical agents are not authorized for pediatric use in Canada due to a lack of pediatric data, not a known specific harm.
Renal and hepatic impairment
Oral carbonic anhydrase inhibitors (acetazolamide, methazolamide) are contraindicated in significant renal or hepatic impairment given the risk of drug accumulation, worsening acidosis, or precipitating hepatic coma; use topical agents preferentially in this population, since their systemic absorption and clearance burden are far lower.
Older adults
The most common population for open-angle glaucoma, and often the population where adherence to a topical drop regimen is most challenged by cost, technique (poor dexterity, difficulty aiming the bottle), or memory. Laser trabeculoplasty is a reasonable earlier option, not only a last resort, in this group. Older adults are also more likely to be on interacting systemic cardiac or respiratory medications, making the beta-blocker screening step in every glaucoma prescription review especially important.
Monitoring & Follow-Up
Recheck IOP about 4 weeks after starting or changing any topical therapy, since the full pressure-lowering effect takes time to stabilize — this is a hard rule for beta-blockers specifically, but is good practice for every class. At scheduled follow-up, reassess automated visual fields and optic disc appearance (photography or imaging) for progression, not just the IOP number in isolation, since a numeric target can be met while the disc or field is still worsening. Adjust the individualized target IOP downward whenever progression continues despite reaching the prior target. After an acute angle-closure attack, recheck IOP within the first hour of emergency treatment and periodically thereafter, and examine the fellow eye — it carries a meaningfully increased risk of a future attack of its own and should be evaluated for prophylactic laser iridotomy. At every refill, re-screen for new systemic disease (asthma, COPD, bradycardia, heart block) or a newly started interacting drug that would change the safety of an existing topical beta-blocker.
Common Errors to Avoid
- Assuming a normal IOP reading rules out glaucoma — a meaningful proportion of people with glaucoma have IOP within the statistically normal range.
- Mistaking acute angle-closure glaucoma for conjunctivitis, migraine, or gastroenteritis — missing the red flags delays truly emergency care.
- Giving pilocarpine as the very first drug in acute angle-closure — at very high IOP the iris sphincter is ischemic and will not respond; other agents must lower IOP first.
- Prescribing or refilling a topical beta-blocker without asking about asthma, COPD, or bradycardia/heart block — a genuinely serious systemic-absorption risk pharmacists are positioned to catch.
- Not counselling on punctal occlusion or eyelid closure — a simple technique that meaningfully reduces systemic absorption and side effects for every topical glaucoma medication, especially beta-blockers.
- Missing a medication-review opportunity — not flagging a new systemic anticholinergic, topiramate, or bupropion prescription in a patient with known narrow angles or significant hyperopia.
- Assuming more frequent dosing of a prostaglandin analogue improves control — more than once daily actually reduces the pressure-lowering effect.
- Combining two prostaglandin analogues, or two topical beta-blockers, together — no added benefit, only added cost and side effects.
- Recommending cannabis for IOP control — short duration of action and psychotropic effects make it an inappropriate glaucoma treatment.
- Failing to arrange examination and prophylactic laser iridotomy for the fellow eye after an acute angle-closure attack in one eye.
Clinical Decision Algorithm
Drug Tables
How to use this table: doses are adult doses for ophthalmic solutions unless stated otherwise, and require patient-specific confirmation. Select any drug name to open its complete Pharmasist Drug Database page. All topical agents reach the systemic circulation to some degree through nasolacrimal drainage — punctal occlusion after every drop meaningfully reduces this (see Non-Pharmacologic Treatment).
Prostaglandin analogues, ophthalmic
First-line therapy for most patients with open-angle glaucoma given effectiveness, once-daily dosing, and a favourable systemic safety profile. [1]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Latanoprost | Adults: 1 drop in the affected eye(s) once daily in the evening | Conjunctival hyperemia, foreign body sensation, permanent iris pigmentation darkening, eyelash growth, periocular skin darkening | Avoid combining with another prostaglandin analogue — paradoxical IOP elevation reported; space at least 5 minutes from thimerosal-containing drops | First-line for most patients. Once-daily evening dosing only — more frequent use reduces effect. Counsel on permanent eye colour change, especially with one-eye treatment. |
| Travoprost | Adults: 1 drop once daily in the evening | Same class effects as latanoprost | Avoid combining with another prostaglandin analogue | Available in a non-benzalkonium chloride preserved formulation (Izba). |
| Bimatoprost | Adults: 1 drop once daily in the evening | Same class effects; somewhat more conjunctival hyperemia | Avoid combining with another prostaglandin analogue | Do not exceed once-daily dosing. |
| Tafluprost | Adults: 1 drop once daily in the evening, from a fresh single-dose unit | Same class effects as other prostaglandin analogues | Avoid combining with another prostaglandin analogue | Preservative-free, single-dose units — preferred when preservative sensitivity or significant ocular surface disease is present. |
| Latanoprostene bunod | Adults: 1 drop once daily in the evening | Same class effects as other prostaglandin analogues | Avoid combining with another prostaglandin analogue | A nitric-oxide-donating latanoprost derivative that increases both uveoscleral and trabecular meshwork outflow. |
Beta-blockers, ophthalmic
Reduce IOP by decreasing aqueous humor production. A meaningful fraction of every dose is absorbed systemically — screen for asthma, COPD, and cardiac conduction disease before every prescription and refill.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Timolol | Adults: 1 drop of the 0.5 percent solution once or twice daily | Systemic beta-blockade: bradycardia, hypotension, bronchospasm, masked hypoglycemia, depression | Additive with oral beta-blockers, calcium channel blockers, digoxin, and other antiarrhythmics; CYP2D6 inhibitors raise levels | Contraindicated in asthma, reactive airway disease, or severe COPD, and in significant bradyarrhythmia or heart block. Counsel on punctal occlusion. |
| Betaxolol | Adults: 1 drop once or twice daily | Same systemic risk profile as timolol but somewhat lower respiratory risk (relatively beta-1-selective) | Same as timolol | May be used with caution in mild COPD when a non-beta-blocker option is unsuitable; still avoid in asthma. |
Alpha-2 adrenergic agonists, ophthalmic
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Brimonidine | Adults: 1 drop 2 to 3 times daily depending on strength | Local allergic reaction, dry mouth, drowsiness, hypotension | Contraindicated with MAO inhibitors | Contraindicated in infants and young children — CNS depression and apnea risk. The 0.15 percent (purite-preserved) formulation may cause less ocular allergy than 0.2 percent. |
| Apraclonidine | Adults: 1 to 2 drops, may repeat | Local allergic reaction, dry mouth, tachycardia, hypotension | Contraindicated with MAO inhibitors | Reserved for short-term or perioperative use — a high rate of allergic blepharoconjunctivitis limits chronic use. |
Carbonic anhydrase inhibitors, ophthalmic
Lower systemic exposure than an oral carbonic anhydrase inhibitor; useful add-on or alternative for a beta-blocker-intolerant patient.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Dorzolamide | Monotherapy: 1 drop 3 times daily Adjunctive therapy: 1 drop twice daily | Bitter, sour, or unusual taste; stinging; local allergic reaction | None significant given minimal systemic absorption | |
| Brinzolamide | Adults: 1 drop twice daily, may increase to 3 times daily after 4 weeks if response is inadequate | Bitter, sour, or unusual taste; blurred vision; local allergic reaction | None significant given minimal systemic absorption | Often more comfortable on instillation than dorzolamide. |
Cholinergic agonist, ophthalmic
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Pilocarpine | Chronic open-angle use (uncommon): 1 drop of the 1 to 4 percent solution 4 times daily Acute angle-closure adjunct: 1 drop of the 1 to 2 percent solution once IOP begins to fall with other emergency agents, may repeat once at 15 minutes | Miosis with reduced night vision, accommodative spasm/myopic shift, brow ache, rare retinal detachment | None significant | Poorly tolerated for chronic use, especially in children and younger adults. Ineffective at very high IOP due to iris sphincter ischemia — never the first drug given for an acute attack. |
Fixed-combination products, ophthalmic
More convenient and may improve adherence for patients who need more than one agent class to reach target IOP; also reduce cumulative preservative exposure and washout from sequential dosing. [6]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Brimonidine / timolol | Adults: 1 drop twice daily | Combined adverse effects of both components | Same as the individual components | |
| Brinzolamide / timolol | Adults: 1 drop twice daily, may increase to 3 times daily after 4 weeks if response is inadequate | Combined adverse effects of both components | Same as the individual components | |
| Dorzolamide / timolol | Adults: 1 drop twice daily | Combined adverse effects of both components | Same as the individual components | |
| Latanoprost / timolol | Adults: 1 drop once daily | Combined adverse effects of both components | Same as the individual components | |
| Travoprost / timolol | Adults: 1 drop once daily, morning or evening | Combined adverse effects of both components | Same as the individual components | Formulated with a non-benzalkonium chloride preservative. |
| Brinzolamide / brimonidine | Adults: 1 drop twice daily, may increase to 3 times daily after 4 weeks if response is inadequate | Combined adverse effects of both components, including somnolence | Contraindicated with MAO inhibitors | The first non-beta-blocker fixed combination — a genuine option for patients whose respiratory or cardiac comorbidities restrict beta-blocker use. |
Carbonic anhydrase inhibitors, oral
Systemic agents reserved for the acute angle-closure emergency sequence and for short-term or adjunctive use in chronic disease, given a substantial rate of systemic intolerance with prolonged therapy.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Acetazolamide | Emergency (acute angle-closure): 500 mg PO or IV once, then 250 mg PO/IV every 6 hours as needed Chronic open-angle adjunct: 250 mg PO 1 to 4 times daily | Paresthesias of the extremities, metabolic acidosis, hypokalemia, GI upset, urolithiasis, drowsiness, rare severe skin or blood reactions | Caution with other sulfonamide-based drugs, high-dose salicylates, and other agents affecting electrolytes | Core emergency drug for acute angle-closure. Contraindicated in significant hepatic or renal impairment. Sulfonamide-related caution on initiation is not an absolute cross-reactivity contraindication with a sulfa-antibiotic allergy. |
| Methazolamide | Adults: 50 to 100 mg PO 2 to 3 times daily | Paresthesias, GI upset, drowsiness, mental confusion, rare severe skin or blood reactions | Caution with other sulfonamide-based drugs, high-dose salicylates, and potassium-depleting diuretics | Generally milder systemic effects than acetazolamide. Contraindicated in significant hepatic or renal impairment. |
Osmotic (hyperosmotic) agent — emergency use only
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Mannitol | Adults: IV, weight-based, per institutional protocol | Fluid overload, electrolyte shifts, headache, nausea | Use with caution alongside other agents affecting fluid/electrolyte balance | Reserve for acute angle-closure IOP not controlled by combined topical and oral agents within about an hour. Use with particular caution in cardiac or renal impairment given the fluid shift. |
Rho-kinase inhibitors (e.g. netarsudil) are a newer topical class used in some other countries but are not currently marketed in Canada, so no Canadian dosing is given here.
References
- Primary Open-Angle Glaucoma Preferred Practice Pattern — Ophthalmology, American Academy of Ophthalmology Preferred Practice Pattern Glaucoma Committee (Gedde SJ, Bowden EC, Challa P, Vinod K, Kolomeyer NN, Chopra V, Budenz DL). Ophthalmology 2026;133(4):P1-P103
- Primary Angle-Closure Disease Preferred Practice Pattern — Ophthalmology, American Academy of Ophthalmology Preferred Practice Pattern Glaucoma Committee (Gedde SJ, Chopra V, Vinod K, Bowden EC, Kolomeyer NN, Challa P, Budenz DL). Ophthalmology 2026;133(4):P153-P201
- Topiramate-associated acute, bilateral, secondary angle-closure glaucoma — Ophthalmology (Fraunfelder FW, Fraunfelder FT, Keates EU). Ophthalmology 2004;111(1):109-111
- Risk of angle-closure glaucoma with bupropion and topiramate — JAMA Ophthalmology (Symes RJ, Etminan M, Mikelberg FS). JAMA Ophthalmol 2015;133(10):1187-1189
- Emergency management: angle-closure glaucoma — Community Eye Health (Murray D). Community Eye Health 2018;31(103):64
- Medical Management of Glaucoma in the 21st Century from a Canadian Perspective — Journal of Ophthalmology (Harasymowycz P, Birt C, Gooi P, Heckler L, Hutnik C, Jinapriya D, Shuba L, Yan D, Day R). J Ophthalmol 2016;2016:6509809
- Improving the therapeutic index of topically applied ocular drugs — Archives of Ophthalmology (Zimmerman TJ, Kooner KS, Kandarakis AS, Ziegler LP). Arch Ophthalmol 1984;102(4):551-553
Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.