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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Commonest form of glaucoma — chronic, bilateral, often asymptomatic until advanced visual field loss
- Key triad: raised IOP (>21 mmHg in most but NOT all cases), optic disc cupping (increased cup-to-disc ratio), and visual field defects
- NICE NG81 (2022 update): 360° selective laser trabeculoplasty (SLT) is now first-line treatment for newly diagnosed POAG and OHT with IOP ≥24 mmHg
- If SLT insufficient: prostaglandin analogue eye drops (latanoprost) are first-line pharmacological treatment
- Normal-tension glaucoma = optic disc damage and field loss with IOP consistently ≤21 mmHg — still treat to lower IOP
Overview
Primary open-angle glaucoma (POAG) is a chronic, progressive optic neuropathy characterised by loss of retinal ganglion cells and their axons, resulting in optic disc cupping and corresponding visual field defects. The drainage angle remains open (unlike angle-closure glaucoma), but there is increased resistance to aqueous outflow through the trabecular meshwork. Raised IOP is the major modifiable risk factor, though approximately 30% of POAG patients have IOP within the normal range (normal-tension glaucoma). The condition is typically bilateral but often asymmetric.
Epidemiology
POAG is the leading cause of irreversible blindness worldwide and the commonest form of glaucoma in the UK, affecting approximately 2% of the population over 40. Prevalence increases sharply with age, reaching 5–10% in those over 80. People of African-Caribbean descent have a 4–8 times higher risk. Other risk factors include family history (first-degree relative with glaucoma), myopia, diabetes, and thin central corneal thickness. The condition is often detected incidentally during routine optometric examination because early disease is asymptomatic.
Clinical Features
Symptoms
Typically ASYMPTOMATIC in early and moderate disease — often detected on routine eye testing
Gradual peripheral visual field loss (tunnel vision) — patient may not notice until advanced
Difficulty with night vision and contrast sensitivity
Bumping into objects on the affected side
Central vision preserved until late disease
Rapid visual deterioration or eye pain suggests alternative diagnosis
Signs
Raised IOP on tonometry (>21 mmHg in most cases, but can be normal in normal-tension glaucoma)
Optic disc cupping — increased cup-to-disc ratio (>0.7 or asymmetry >0.2 between eyes)
Disc pallor, notching (especially inferotemporal), disc haemorrhage
Retinal nerve fibre layer (RNFL) thinning on OCT
Visual field defects: arcuate scotoma, nasal step, paracentral scotoma (on formal perimetry)
Open angle on gonioscopy (distinguishes from angle-closure)
Investigations
First-line
Goldmann applanation tonometryGold standard for IOP measurement. Normal 10–21 mmHg but IOP alone does not diagnose POAG
Slit-lamp biomicroscopy and fundoscopyAssess optic disc appearance — cup-to-disc ratio, rim thinning, disc haemorrhage, RNFL defects
Visual field testing (standard automated perimetry)Humphrey or equivalent — detects characteristic glaucomatous field defects (arcuate scotoma, nasal step)
Second-line
Optical coherence tomography (OCT)Quantitative assessment of RNFL thickness and ganglion cell analysis — detects structural damage before visual field loss
GonioscopyConfirms open angle — essential to exclude angle-closure mechanism
Central corneal thickness (CCT)Thin corneas underestimate true IOP; thick corneas overestimate. CCT <555 µm is a risk factor for progression
Specialist
Optic disc photographyBaseline and serial documentation for monitoring progression
Diurnal IOP curveMay be helpful when IOP appears normal on single measurements but damage is progressing
1
First-line: 360° selective laser trabeculoplasty (SLT)
- NICE NG81 (2022 update) recommends 360° SLT as initial treatment for newly diagnosed POAG or OHT with IOP ≥24 mmHg
- SLT can delay or avoid the need for daily eye drops
- May need repeat treatment if benefit wanes over time
- Counsel patient about temporary post-procedure inflammation and IOP spike
2
Pharmacological treatment (if SLT insufficient or declined)
- First-line: prostaglandin analogue — latanoprost 0.005% once daily in the evening
- Second-line: beta-blocker (timolol 0.5% BD), or carbonic anhydrase inhibitor (dorzolamide), or sympathomimetic (brimonidine)
- Combination drops if monotherapy insufficient (e.g. latanoprost-timolol fixed combination)
- Preservative-free drops for patients with ocular surface disease or preservative allergy
3
Surgery (if medical and laser treatment insufficient)
- Trabeculectomy — creates a new drainage pathway (bleb) under the conjunctiva
- Aqueous shunt device (tube surgery) — alternative if trabeculectomy fails or high risk
- Minimally invasive glaucoma surgery (MIGS) — iStent, XEN gel stent — increasingly used
- Cyclodiode laser — reduces aqueous production; reserved for refractory cases
4
Monitoring and follow-up
- Lifelong monitoring required — IOP, visual fields, and optic disc assessment
- Frequency guided by risk of progression and disease severity
- Target IOP is individualised — generally aim for ≥20% reduction from baseline
Complications
- Progressive visual field loss: Leading to tunnel vision and eventually blindness if untreated
- Impact on daily activities: Driving (must meet DVLA visual field standards), mobility, falls risk
- Treatment side effects: Prostaglandin analogues — iris colour change, periorbital fat atrophy, eyelash growth; beta-blockers — bronchospasm, bradycardia; surgery — hypotony, bleb leak, endophthalmitis
- Normal-tension glaucoma: Progression despite apparently normal IOP — requires aggressive IOP lowering
UKMLA Exam Tips
- 1POAG = open angle + raised IOP + optic disc cupping + visual field loss. It is PAINLESS and ASYMPTOMATIC until late — classic "silent thief of sight"
- 2Key update: SLT is now FIRST-LINE per NICE NG81 (2022) — not just eye drops
- 3Latanoprost (prostaglandin analogue) is the first-line DROP if pharmacological treatment is needed
- 4Do NOT prescribe timolol (beta-blocker) in patients with asthma or COPD — use a prostaglandin analogue instead
- 5Normal-tension glaucoma = glaucomatous disc/field damage with IOP ≤21 — still requires treatment to lower IOP further
- 6Disc haemorrhage on fundoscopy is a red flag for glaucoma progression
- 7DVLA: must meet binocular visual field requirements — patients must notify DVLA if diagnosed with glaucoma
practicetest your knowledge on primary open-angle glaucomaApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — ophthalmology and beyond.
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