Acute Angle-Closure Glaucoma and Primary Open-Angle Glaucoma are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Acute Angle-Closure Glaucoma vs Primary Open-Angle Glaucoma at a glance
Acute Angle-Closure Glaucoma: Ophthalmologic emergency — sudden IOP elevation from blocked aqueous outflow; vision loss if not treated within hours.
Primary Open-Angle Glaucoma: Chronic painless optic neuropathy with progressive visual field loss — leading cause of irreversible blindness worldwide.
Try two board-style questions on Acute Angle-Closure Glaucoma vs Primary Open-Angle Glaucoma
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Question 1EENTMedium
A 67-year-old farsighted woman presents to urgent care with 4 hours of severe left eye pain, blurred vision with colored halos around lights, and vomiting that began while she was seated in a dimly lit restaurant. On exam the left globe is rock-hard to palpation, the cornea appears steamy, and the pupil is fixed at a mid-dilated 6 mm. Tono-Pen intraocular pressure is 62 mmHg in the left eye and 15 mmHg in the right. Acute angle-closure glaucoma is diagnosed. Which of the following best explains the findings?
AIncreased aqueous production by a chronically hypersecreting ciliary body
BNeovascular membrane contracting and scarring the anterior chamber angle
CInflammatory cells and protein clogging the trabecular meshwork outflow tract
DIris apposition to the lens blocking aqueous flow into the anterior chamber
Reveal answer & full explanation
Correct answer: D — Iris apposition to the lens blocking aqueous flow into the anterior chamber
AIncreased aqueous production by a chronically hypersecreting ciliary body
BNeovascular membrane contracting and scarring the anterior chamber angle
CInflammatory cells and protein clogging the trabecular meshwork outflow tract
DIris apposition to the lens blocking aqueous flow into the anterior chamber✓
Why Iris apposition to the lens blocking aqueous flow into the anterior chamber is correct
In an anatomically crowded eye (shallow anterior chamber, common in hyperopes), the mid-dilated pupil maximizes contact between the iris and the anterior lens surface, producing pupillary block.
Aqueous cannot pass from the posterior to the anterior chamber, so it accumulates behind the iris and bows the peripheral iris forward (iris bombe), pressing it against the trabecular meshwork and acutely obstructing outflow.
The resulting IOP spike (often 40-80 mmHg) causes the steamy edematous cornea, mid-dilated poorly reactive pupil, rock-hard globe, and pain. Dim-light or movie-theater exposure is a classic trigger.
Why the others are wrong
Inflammatory cells and protein clogging the trabecular meshwork outflow tract is the mechanism of uveitic glaucoma; anterior uveitis presents with ciliary flush, cells and flare, and a typically miotic pupil with normal or low IOP, not a mid-dilated fixed pupil with very high pressure.
Increased aqueous production by a chronically hypersecreting ciliary body is not the problem; acute angle closure is an outflow-obstruction process, and aqueous suppressants help by lowering already-normal production rather than correcting overproduction.
Neovascular membrane contracting and scarring the anterior chamber angle describes neovascular glaucoma from chronic retinal ischemia (diabetic retinopathy, central retinal vein occlusion), which causes gradual angle closure with rubeosis iridis, not a sudden pupillary-block attack triggered by dim light.
Question 2EENTMedium
A 65-year-old male with 20 years of open-angle glaucoma on latanoprost and timolol has worsening visual field loss with intraocular pressure (IOP) not at target. Selective laser trabeculoplasty (SLT) is being considered. Which of the following best describes the mechanism of SLT?
AThermal photocoagulation ablation of the trabecular meshwork connective tissue
BLaser creation of a full-thickness fistula through the trabecular meshwork
CCiliary muscle contraction that widens the trabecular meshwork spaces
DSelective photothermolysis of pigmented trabecular meshwork cells
Reveal answer & full explanation
Correct answer: D — Selective photothermolysis of pigmented trabecular meshwork cells
AThermal photocoagulation ablation of the trabecular meshwork connective tissue
BLaser creation of a full-thickness fistula through the trabecular meshwork
CCiliary muscle contraction that widens the trabecular meshwork spaces
DSelective photothermolysis of pigmented trabecular meshwork cells✓
Why Selective photothermolysis of pigmented trabecular meshwork cells is correct
The laser selectively targets melanin-containing trabecular meshwork cells without damaging adjacent non-pigmented cells (selective photothermolysis)
This triggers macrophage recruitment and trabecular remodeling, improving aqueous outflow and reducing intraocular pressure (IOP)
Why the others are wrong
Thermal photocoagulation ablation of the trabecular meshwork connective tissue — describes argon laser trabeculoplasty (ALT), which causes more thermal damage; SLT spares surrounding non-pigmented tissue (confused-with ALT)
Laser creation of a full-thickness fistula through the trabecular meshwork — describes laser trabeculostomy (for example, excimer laser trabeculostomy), which opens channels through the meshwork into the Schlemm canal; SLT creates no opening and leaves the meshwork architecture intact, lowering IOP through a biologic remodeling response instead (confused-with trabeculostomy)
Ciliary muscle contraction that widens the trabecular meshwork spaces — describes cholinergic agonists such as pilocarpine, whose ciliary muscle contraction pulls on the scleral spur to open the meshwork; SLT acts directly on the pigmented meshwork cells and does not work through the ciliary muscle (confused-with pilocarpine)
Additional high-yield points
LiGHT trial (Lancet 2019): with first-line SLT, about 74% of patients needed no glaucoma drops at 3 years and IOP was at target at about 93% of visits; quality of life (the primary outcome) was similar to first-line drops
Typical IOP reduction: 20-30%
SLT is repeatable approximately every 5 years
Compared with ALT: equivalent efficacy with less thermal damage
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Ophthalmologic emergency — sudden IOP elevation from blocked aqueous outflow; vision loss if not treated within hours.
Chronic painless optic neuropathy with progressive visual field loss — leading cause of irreversible blindness worldwide.
Classic presentation
Steamy cornea + mid-dilated fixed pupil + rock-hard eye with severe pain in a hyperopic older woman.; Sudden severe unilateral eye pain and headache; Blurred vision and halos around lights (corneal edema); Nausea and vomiting (vagal response) — often misdiagnosed as abdominal/GI process; Photophobia; Symptoms may follow dim-light…
Progressive optic disc cupping with corresponding nerve fiber bundle visual field defects in a patient with elevated IOP.; Asymptomatic in early disease — vision loss is painless and gradual; Patients rarely notice peripheral field defects until advanced; Trouble with night driving, missing steps, or bumping into things; Central vision…
Workup / key labs
Clinical triad: acute pain + corneal edema + IOP >30 mmHg with closed angle on gonioscopy.; No labs delay treatment — clinical diagnosis
Characteristic optic disc and/or nerve fiber layer damage with corresponding visual field defect in an eye with open angle, after exclusion of secondary causes.; Not routinely indicated for diagnosis; Targeted workup (B12, ESR, ACE, syphilis, etc.) if optic neuropathy appears non-glaucomatous
Imaging
Goldmann or Tono-Pen IOP measurement — primary objective; Slit-lamp examination: shallow anterior chamber, corneal edema, mid-dilated pupil; Gonioscopy after IOP control — confirms closed angle, evaluates fellow eye; Anterior segment OCT or ultrasound biomicroscopy in equivocal cases
Goldmann applanation tonometry (gold standard) — multiple readings, diurnal variation; Pachymetry — central corneal thickness influences IOP measurement and is an independent risk factor (OHTS); Gonioscopy — confirms open angle and rules out angle closure and secondary causes; Dilated fundus exam and stereoscopic optic disc photography;…
First-line treatment
IMMEDIATE ophthalmology consult — vision is time-dependent; Position patient supine to allow lens to fall posteriorly; Topical aqueous suppressants in rapid succession (every minute × 3 then standard dosing):; • Topical beta-blocker — timolol 0.5%; • Topical alpha-2 agonist — apraclonidine 1% or brimonidine 0.2%; • Topical carbonic…
Target IOP reduction of 20-30% from baseline; lower targets for advanced disease (EMGT, AGIS data); Prostaglandin analog (POAG) — latanoprost, bimatoprost, travoprost, tafluprost — once daily at bedtime; most effective IOP-lowering class; side effects: iris darkening, periorbital pigmentation/atrophy, lash growth, conjunctival…
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