Glaucoma — Open and Closed Angle

Aqueous Humor Dynamics and IOP Regulation

• Aqueous humor is produced by the ciliary body epithelium (ultrafiltration and active secretion) at a rate of approximately 2–3 μL/min, with turnover occurring every 90 minutes
• Under normal conditions, 85–90% of aqueous humor drains through the conventional pathway (trabecular meshwork → Schlemm's canal → aqueous veins), while 10–15% drains through the unconventional uveoscleral pathway
• IOP is determined by the equation: IOP = (aqueous production / aqueous outflow) + episcleral venous pressure
• Normal IOP ranges from 10–21 mmHg, but some individuals with IOP >21 mmHg remain stable ("ocular hypertensives"), while others with IOP <21 mmHg develop glaucomatous damage ("normal-tension glaucoma")
• IOP fluctuates diurnally by 2–6 mmHg, with highest pressures typically in the morning

Open-Angle Glaucoma Pathophysiology

• The fundamental defect involves increased resistance to conventional outflow through the trabecular meshwork despite a patent, anatomically open anterior chamber angle
• Histopathologic changes include increased extracellular matrix deposition, thickened basement membranes, loss of cellularity, and reduced endothelial function within the trabecular meshwork
• Molecular mechanisms involve:
• Oxidative stress from chronic IOP elevation, leading to accumulation of reactive oxygen species (ROS) that overwhelm antioxidant defenses
• Mitochondrial dysfunction in trabecular meshwork cells and retinal ganglion cells, impairing energy metabolism
• Loss of endothelial nitric oxide (NO) production, reducing vasodilation and aqueous outflow
• Upregulation of transforming growth factor-beta (TGF-β) and other fibrogenic cytokines promoting extracellular matrix remodeling
• Altered aquaporin-1 and aquaporin-5 expression, affecting water transport
• Genetic predisposition involves mutations in genes including MYOC (myocilin; POAG1 locus), OPTN (optineurin), WDR36, NTF4, and FOXC1 in familial forms
• The mechanotransduction hypothesis suggests trabecular meshwork cells detect mechanical strain from elevated pressure, triggering pathologic gene expression via Rho kinase activation

Closed-Angle Glaucoma Pathophysiology

• The anatomic basis involves pupillary block, where the iris is pushed forward against the lens, blocking aqueous flow from the posterior to anterior chamber
• Predisposing factors include a relatively small eye (hyperopia/micropsia), thick crystalline lens, short axial length, narrow anterior chamber depth, and anteriorly positioned lens
• In acute angle closure, sudden IOP elevation (often 40–80 mmHg) occurs when the peripheral iris completely occludes the trabecular meshwork
• The mechanism typically involves:
• Pupillary block: increased lens-iris contact impairs aqueous flow, raising posterior chamber pressure
• Iris bowing: pressure differential forces the peripheral iris forward against the trabecular meshwork
• In some cases, plateau iris anatomy (anteriorly positioned ciliary processes) mechanically pushes the iris forward even after laser peripheral iridotomy
• Predisposing conditions include hyperopia, anterior chamber shallowing with aging, thick lenses (post-cataract extraction), and medications that dilate pupils or increase aqueous production
• Secondary angle closure can result from inflammation (uveitis), neovascularization (diabetic retinopathy, retinal ischemia), lens expansion (phacomacrophic glaucoma), or ciliary block (aqueous misdirection)

Retinal Ganglion Cell Injury and Optic Nerve Damage

• Mechanical stress from elevated IOP compresses axons at the lamina cribrosa, disrupting axonal transport
• Ischemia from IOP-induced vascular insufficiency activates intrinsic apoptotic pathways
• Excitotoxicity from glutamate accumulation activates NMDA and AMPA receptors, causing calcium influx and neuronal death
• Chronic inflammation and glial activation (Müller cells, microglia, astrocytes) produce pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) perpetuating neurodegeneration
• Loss of brain-derived neurotrophic factor (BDNF) and reduced nerve growth factor (NGF) signaling impair survival mechanisms
• Progressive optic disc cupping results from preferential loss of axons at the disc margin, causing backward bowing of the lamina cribrosa

Primary Open-Angle Glaucoma (POAG)

• Accounts for 80–85% of all glaucoma cases in Caucasian populations; prevalence increases significantly in African and Hispanic populations
• No identifiable secondary cause; pathophysiology centered on trabecular meshwork dysfunction
• Major risk factors: elevated baseline IOP (especially >26 mmHg), older age (>60 years), African or Hispanic ethnicity, first-degree family history of glaucoma, myopia, reduced corneal thickness (<555 μm by pachymetry), optic disc cupping (cup-to-disc ratio >0.5), and previous ocular hypertension
• The Ocular Hypertension Treatment Study (OHTS) identified that 5-year risk of conversion to glaucoma ranged from 1% (younger age, lower IOP, thicker cornea) to 26% (older age, higher IOP, thinner cornea, more cupping)
• Genetic factors: mutations in MYOC (15–20% of familial POAG), OPTN (2–4%), and WDR36 account for most monogenic inheritance patterns; genome-wide association studies (GWAS) identify >30 loci associated with susceptibility
• Non-genetic factors: smoking, corticosteroid use, thyroid eye disease, and possibly diabetes

Normal-Tension Glaucoma (NTG)

• Subset of POAG where glaucomatous optic nerve damage occurs despite consistently normal IOP measurements (<21 mmHg)
• Accounts for 25–35% of POAG in Japanese populations, 15–25% in Caucasians
• Likely represents greater individual susceptibility to IOP-independent vascular insufficiency or structural weakness
• Risk factors: systemic hypotension, nocturnal blood pressure dips, anemia, sleep apnea, vasospastic disorders (migraine), and positive family history
• Diagnosis requires documentation of normal IOP on multiple measurements (including 24-hour IOP curves) with confirmatory optic nerve damage

Primary Angle-Closure Glaucoma (PACG)

• Accounts for 10–15% of glaucoma cases; prevalence varies significantly by ethnicity (10–20% in East Asian populations vs. <1% in Caucasians)
• Anatomic predisposition: hyperopia or micropsia (short axial length, strong hyperopic refraction), shallow anterior chamber depth (<2.5 mm), thick crystalline lens, short axial length (<22 mm), and anteriorly positioned ciliary processes
• Ethnicity: significantly higher prevalence in Inuit, East Asian (Chinese, Korean, Vietnamese), Hispanic, and South Asian populations
• Female predominance: 2–4:1 (due to smaller eyes and shorter axial lengths on average)
• Age-related: predisposition increases with older age as lens thickens and anterior chamber continues to shallow
• Medications triggering acute angle closure: mydriatics (atropine, tropicamide, phenylephrine), sympathomimetics (pseudoephedrine, topiramate, sertraline), antihistamines, anticholinergics, and selective serotonin reuptake inhibitors (SSRIs)
• Fellow eye involvement: 50–80% of untreated patients will experience angle closure in the fellow eye within 5–10 years

Secondary Glaucomas with Elevated IOP

• Neovascular glaucoma: retinal ischemia from proliferative diabetic retinopathy, central retinal vein occlusion, or ischemic ocular ischemic syndrome causes iris neovascularization and angle closure
• Phacomorphic glaucoma: leakage of lens proteins through intact capsule of intumescent cataract causes macrophage-mediated trabecular meshwork obstruction
• Lens particle glaucoma: disrupted lens cortex releases proteinaceous material
• Pseudoexfoliation: extracellular proteinaceous material deposits on lens capsule, iris, and trabecular meshwork, causing elevated IOP and angle closure risk
• Uveitic glaucoma: inflammatory cells obstruct trabecular meshwork or form posterior synechiae (angle closure); associated with granulomatous anterior uveitis
• Corticosteroid-induced glaucoma: exogenous or inhaled corticosteroids increase trabecular meshwork outflow resistance; occurs in 5–40% of glaucoma patients using steroids chronically
• Exfoliative glaucoma: trauma causes Descemet's membrane disruption with subsequent trabecular meshwork clogging
• Ghost cell glaucoma: RBC debris from vitreous hemorrhage occludes trabecular meshwork

Open-Angle Glaucoma (OAG) Presentation

• Asymptomatic disease: OAG is notoriously silent; the majority of patients with early-to-moderate disease report no symptoms and are detected only on routine screening
• This "silent thief of sight" nature makes population screening and family screening critical
• Patients often present only after significant vision loss has occurred
• Progressive peripheral vision loss: the classic pattern occurs at the nasal periphery (nasal scotoma) or develops as an "arcuate scotoma" (following nerve fiber bundle distribution from the optic disc)
• Corresponds to selective loss of superior or inferior retinal nerve fiber layer
• May progress to generalized constriction and eventual central vision involvement in advanced disease
• Often unnoticed by patients until bilateral involvement or monocular testing occurs
• Floaters or blurred vision: nonspecific symptoms reported by some patients, often attributed to other causes
• Optic disc changes:
• Progressive optic cup enlargement: cup-to-disc (C/D) ratio increases over time; normal C/D is <0.3, borderline 0.3–0.5, suspicious >0.5
• Optic disc cupping: vertical cup diameter >horizontal due to preferential superior and inferior axon loss
• Neuroretinal rim thinning and pallor: loss of pink-colored neural tissue at disc margins
• Bayonetting: displacement of major blood vessels at optic disc edge from backward bowing of lamina cribrosa
• Peripapillary atrophy: loss of retinal pigment epithelium and choroid adjacent to optic disc, appearing as hypopigmented halo
• Optic disc hemorrhages: small hemorrhages at disc margin or within retinal nerve fiber layer, particularly at superior/inferior poles
• Retinal nerve fiber layer defects: thinning of the arcuate nerve fiber bundle, appearing as dark linear defects on ophthalmoscopy

Acute Angle-Closure Glaucoma (AACG) Presentation

• Acute onset of severe eye pain and blurred vision: typically develops over hours
• Pain is often described as sharp, shooting, or aching
• Blurred vision with halos around lights is characteristic and pathognomonic
• Halos result from corneal edema scattering light
• Photopsia (light flashes) may occur
• Red eye: moderate injection of conjunctival and ciliary vessels
• Corneal haziness: acute corneal edema from elevated IOP gives the cornea a cloudy, frosted appearance
• Makes visualization of iris and angle details difficult with gonioscopy
• Resolves with IOP reduction
• Mid-dilated, non-reactive pupil: pupil is typically in mid-position (4–6 mm) and responds poorly to light
• Distinguishes from pharmacologic dilation
• Results from transient iris ischemia and posterior synechiae (adhesions between iris and lens)
• Markedly elevated IOP: typically 40–80 mmHg (rarely >60 mmHg unless severe)
• Tonometry shows dramatic pressure elevation on first examination
• Shallow anterior chamber: gonioscopy (if cornea clear enough) shows no angle structures visible; iris appears in contact with cornea
• Peripheral anterior synechiae (PAS): adhesions between iris and angle wall develop as IOP drops if angle remains closed
• Anterior chamber inflammation: cellular reaction and flare from iris ischemia and tissue damage
• Systemic manifestations (from acute IOP elevation):
• Nausea and vomiting (very common, often misdiagnosed as migraine or gastrointestinal pathology)
• Malaise and headache
• Bradycardia and hypotension (vagal response)

Subacute Angle-Closure Glaucoma

• Intermittent episodes of IOP elevation (20–40 mmHg) triggered by pupil dilation
• Prodromal symptoms: blurred vision and halos around lights that resolve with rest or pupil constriction
• May precede acute attack by days to weeks
• Critical to identify and treat, as each episode causes more permanent angle closure (PAS formation)

Chronic Angle-Closure Glaucoma

• Often asymptomatic or mildly symptomatic
• Develops insidiously from unrecognized acute or chronic intermittent episodes
• Presents with optic nerve damage and field loss on screening
• Requires gonioscopy to differentiate from OAG

Physical Examination Findings in Glaucoma

Clinical History and Risk Stratification

• Detailed ocular history: previous eye exams, known family history of glaucoma, prior elevations in IOP, visual symptoms, and ocular trauma
• Systemic history: diabetes, hypertension, vascular disease, sleep apnea, vasospastic conditions (migraine), corticosteroid use (systemic or topical), and medications with mydriatic effects
• **Family history is

Acute angle closure — an ophthalmologic emergency (AAO Primary Angle-Closure Disease PPP)

• Immediate medical IOP lowering, given simultaneously while ophthalmology is called: a topical beta blocker (timolol) to cut aqueous production, a topical alpha-2 agonist (brimonidine or apraclonidine), a topical carbonic anhydrase inhibitor (dorzolamide), plus systemic acetazolamide (500 mg IV or PO) for maximal suppression of ciliary body secretion
• Hyperosmotic agent (IV mannitol) if pressure remains markedly elevated — osmotically dehydrates the vitreous, deepening the anterior chamber; use caution in heart failure and renal impairment
• Pilocarpine (muscarinic agonist) constricts the pupil and pulls the peripheral iris out of the angle, but the sphincter is ischemic and unresponsive at very high IOP, so it is generally added after pressure begins to fall
• Definitive therapy is laser peripheral iridotomy, which bypasses pupillary block; the AAO recommends prophylactic iridotomy of the fellow eye, which shares the same anatomy. Lens extraction is an accepted alternative or adjunct in phacomorphic or lens-driven angle closure

Chronic open-angle glaucoma (AAO Primary Open-Angle Glaucoma PPP)

• Prostaglandin analog (latanoprost) is first-line — increases uveoscleral outflow, once-nightly dosing, no systemic effects
• Selective laser trabeculoplasty is an accepted first-line alternative to drops
• Escalation: add a beta blocker, alpha-2 agonist, topical carbonic anhydrase inhibitor, or a Rho-kinase inhibitor (netarsudil), which lowers trabecular outflow resistance
• Surgery when medical/laser therapy fails or fields progress: trabeculectomy, glaucoma drainage device, or minimally invasive glaucoma surgery
• Goal is a percentage reduction from baseline IOP, not a single universal number; normal-tension glaucoma still requires IOP lowering

Avoid

• Mydriatics/anticholinergics in narrow angles; topical beta blockers in asthma, COPD, bradycardia, or high-grade AV block; brimonidine in infants and young children (apnea, CNS depression)

Complications of the disease

• Irreversible optic neuropathy and blindness: retinal ganglion cell axons do not regenerate, so field loss recovered is zero — signaled by progressive rim thinning and expanding arcuate scotomata on serial perimetry
• Permanent nerve damage from a single acute attack (emergency): sustained pressure above perfusion pressure produces ischemic axonal death within hours; a persistently poor visual acuity and pale disc after IOP normalizes signals it
• Peripheral anterior synechiae → chronic angle closure: repeated or prolonged iris–trabecular apposition scars the angle, so IOP stays high even after a patent iridotomy; gonioscopy shows permanently sealed angle
• Glaukomflecken: small anterior subcapsular lens opacities from lens epithelial necrosis — the tell-tale sign of a prior acute attack; iris sphincter atrophy and a fixed irregular pupil are the companion findings
• Central retinal vein occlusion / ischemic optic neuropathy from acute pressure-driven vascular compromise
• Neovascular glaucoma as an end-stage secondary form — rubeosis iridis visible on slit lamp

Complications of treatment

• Prostaglandin analogs: permanent iris and periocular hyperpigmentation, lash hypertrichosis, periorbital fat atrophy, and cystoid macular edema or uveitis reactivation in susceptible eyes
• Topical beta blockers: systemic absorption via nasolacrimal drainage causing bronchospasm, bradycardia, and blunting of hypoglycemic warning signs
• Brimonidine: follicular allergic conjunctivitis; apnea/somnolence in infants
• Acetazolamide: non-anion-gap metabolic acidosis, hypokalemia, paresthesias, nephrolithiasis, rare aplastic anemia
• Filtering surgery: hypotony with choroidal effusion, bleb leak, and blebitis/endophthalmitis (emergency — pain, hypopyon, sudden vision drop)
• Malignant (aqueous misdirection) glaucoma (emergency): shallow anterior chamber with high IOP despite a patent iridotomy after intraocular surgery

• The acute attack triad: severe unilateral eye pain, halos around lights, and a mid-dilated, fixed, poorly reactive pupil with a steamy/hazy cornea. Nausea and vomiting are so prominent that the stem often disguises the case as gastroenteritis, migraine, or an acute abdomen — the eye finding is the giveaway.
• Single best next step in suspected acute angle closure is tonometry (measure the IOP), then immediate pressure-lowering drops plus acetazolamide and urgent ophthalmology consultation. Do not wait for imaging.
• Gonioscopy is the test that separates open from closed angle — it is the definitive way to visualize the trabecular meshwork, and it is required before labeling any glaucoma "open-angle."
• Definitive treatment of pupillary-block angle closure is laser peripheral iridotomy, done bilaterally — the fellow eye shares the same hyperopic, shallow-chamber anatomy.
• Never dilate a narrow-angle eye: anticholinergic and sympathomimetic agents (including systemic anticholinergics, decongestants, and some antiemetics) precipitate attacks. Conversely, *open*-angle glaucoma is not a contraindication to dilation — a very common distractor.
• The one drug association examiners love: topiramate causes bilateral, simultaneous acute angle closure with an acute myopic shift via ciliary body swelling and supraciliary effusion — this is not pupillary block, so the answer is stop the drug and give aqueous suppressants, not iridotomy.
• Corticosteroids (topical, inhaled, or systemic) raise IOP by increasing trabecular outflow resistance and cause an *open*-angle picture — check pressure in any steroid user with visual complaints.
• Latanoprost is first-line for chronic open-angle disease; expect the stem to mention iris darkening or eyelash growth. Avoid timolol in asthma/COPD and bradyarrhythmia.
• Normal-tension glaucoma still gets IOP-lowering therapy — a pressure under 21 mmHg does not exclude glaucoma, and cupping plus an arcuate field defect makes the diagnosis.