Glaucoma: The Silent Thief of Sight – A GP’s Role in Early Detection and Referral Types

Practice a case with the AI patient 🤖

What my fellow doctor colleague asked:

In cases of chronic glaucoma with mild peripheral visual field changes, should we refer the patient urgently or routinely? Also, should IOP-lowering eye drops be initiated in primary care, or is that solely the responsibility of the specialist?

What is Glaucoma, why it happens, and what to do next

Glaucoma is a group of eye conditions that can lead to progressive, irreversible vision loss due to damage to the optic nerve, often linked to increased pressure inside the eye (intraocular pressure or IOP). It is one of the leading causes of blindness worldwide, yet many patients don’t know they have it until the damage is advanced.

💡 What Causes Glaucoma?

The eye produces a fluid called aqueous humour that nourishes the eye and maintains its shape. This fluid drains through a structure called the trabecular meshwork located at the anterior chamber angle — the space between the cornea and the iris.

Glaucoma occurs when this fluid doesn't drain properly, leading to increased intraocular pressure (IOP). This raised pressure damages the optic nerve at the back of the eye.

Types of Glaucoma & Why the Problem Arises

1. Open-Angle Glaucoma (OAG) / Primary Open-Angle Glaucoma (POAG)

• The angle between the cornea and iris is open, but the drainage system (trabecular meshwork) becomes blocked or dysfunctional over time.

• Aqueous fluid builds up slowly, leading to chronic, painless elevation of IOP.

• The damage is gradual and silent, typically affecting peripheral vision first.

Why the problem arises:

• Age-related degeneration of the drainage pathway

• Genetic predisposition

• Other modifiable and non-modifiable risk factors (see below)

2. Closed-Angle Glaucoma (CAG) / Acute Angle-Closure Glaucoma

• The angle is narrowed or closed, and the fluid can’t drain at all.

• This causes a sudden rise in IOP, triggering acute symptoms and threatening rapid vision loss.

Why the problem arises:

• Anatomically shallow anterior chamber, often in smaller eyes

• Iris bowing forward due to pupil dilation (e.g., in dim light or after medications)

Risk Factors for Glaucoma

📘 General Risk Factors (for both types)

Risk Factor	Explanation
Increasing age	Especially >40 years for POAG and >60 for CAG
Family history	Strong genetic link, especially in POAG
Ethnicity	African/Caribbean descent → ↑ POAG risk

• East Asian descent → ↑ CAG risk || Raised IOP 

• The most important modifiable risk factor

  • || Diabetes | Associated with increased IOP and optic nerve vulnerability

  • || Hypertension | May influence optic nerve blood flow

  • || Steroid use (topical/systemic) | Can increase IOP

🟦 Specific Risk Factors for Open-Angle Glaucoma

Risk Factor	Details
Myopia (short-sightedness)	Increases risk of POAG
Thin central cornea	Linked to higher risk of optic nerve damage
Vascular dysregulation	Linked to normal-tension glaucoma subtype

🟥 Specific Risk Factors for Closed-Angle Glaucoma

Risk Factor	Details
Hyperopia (long-sightedness)	Smaller eyes → narrower angles
Female sex	Narrower angles due to anatomy
Older age	Lens thickening narrows the angle
East Asian or Inuit ancestry	Higher anatomical predisposition
Medications	Anticholinergics, sympathomimetics, antidepressants (can dilate pupil and trigger attack)

What Are the Tests for Glaucoma?

Test	Purpose
Tonometry	Measures intraocular pressure (IOP)
Gonioscopy	Examines the angle to classify open vs. closed angle
Ophthalmoscopy	Assesses optic nerve cupping and damage
Visual Field Test	Detects peripheral vision loss
Optical Coherence Tomography (OCT)	Measures optic nerve fibre thickness

🏥 When and Why to Refer

Glaucoma Type	Referral Type	Why Refer
Open-Angle	Routine	Chronic but progressive; needs specialist confirmation, monitoring, and lifelong treatment
Closed-Angle	Immediate	Can cause blindness within hours without rapid IOP control

GPs do not initiate glaucoma treatment — instead, they play a vital role in early detection, prompt referral, and patient reassurance.

💊 IOP-lowering medications (like prostaglandin analogues) are usually started by the specialist, not the GP.

However, if the patient presents with:

• Ocular discomfort

• Dry eyes

• Concern/anxiety about vision

👩‍⚕️ What the GP can do:

Action	Details
🔍 Reassurance & Explanation	Explain that the condition and referral is in place for specialist assessment.
👁️ Manage Dry Eye (if present)	Artificial tears / lubricating drops (e.g., hypromellose) can be offered for comfort — these do not lower IOP.
📄 Advise Avoidance of Steroids	Caution against use of over-the-counter steroid eye drops (which may raise IOP).
📞 Facilitate Routine Referral	Ensure the patient is referred for formal assessment and management — usually via optometrist or directly to ophthalmology.
🧠 Address Anxiety	Acknowledge any patient anxiety and provide written material or online resources.

🚫 GPs should not prescribe IOP-lowering eye drops unless instructed by ophthalmology, as inappropriate use may mask worsening or complicate diagnosis.

💊 Management

Open-Angle Glaucoma

• First-line: Prostaglandin analogues (e.g., latanoprost) to lower IOP

• Other drops: Beta-blockers, carbonic anhydrase inhibitors, alpha-agonists

• Laser trabeculoplasty or surgical trabeculectomy if not controlled with drops

• Regular monitoring of IOP, visual fields, and optic nerve

🩺 Started and managed by ophthalmologists — not initiated in primary care.

🚨 Red Flag Symptoms

• IOP >= 35 mm of Hg without symptoms --> Urgent Referral

• IOP >= 35 mm of Hg with symptoms --> Immediate Referral

  • Sudden, severe eye pain

  • Red, hard eye

  • Blurred vision, halos around lights

  • Headache, nausea, vomiting

  • Mid-dilated, fixed pupil

  • Cloudy cornea

Closed-Angle Glaucoma

• Immediate treatment to lower IOP:

  • Acetazolamide (IV or oral)

  • Topical beta-blockers or alpha-agonists

• Definitive treatment:

  • Laser peripheral iridotomy (creates a small hole in the iris to open the angle)

• May require surgery if recurrent

🆘 Requires emergency ophthalmology referral.

These signs indicate an ophthalmic emergency — Immediate referral is essential.

Why Early Detection and Referral Matter

• Vision loss from glaucoma is irreversible — but early treatment slows or halts progression.

• Patients are often asymptomatic in the early stages (especially in open-angle glaucoma).

• By the time symptoms are noticed, permanent damage may already be done.

• Referring promptly ensures patients access specialist evaluation, accurate diagnosis, tailored treatment, and lifelong follow-up.

📝 Summary: Quick Glance Comparison

Feature	Open-Angle	Closed-Angle
Onset	Gradual	Sudden
Symptoms	Usually asymptomatic	Painful, red eye, nausea
IOP	Mild to moderately raised	Severely raised
Vision Loss	Gradual peripheral vision loss	Rapid vision loss if untreated
Referral	Routine	Immediate
Treatment	IOP-lowering drops, laser/surgery	Emergency IOP reduction + laser iridotomy

Key Takeaway for GPs and PLAB Candidates

• Always refer suspected glaucoma — early detection saves sight.

• Do not start treatment in primary care — it’s specialist-led.

• Recognize red flags for acute angle-closure — these are true ophthalmic emergencies.

• Reassure, educate, and support the patient through the referral process.

📚 References

• https://www.nice.org.uk/guidance/qs180/chapter/quality-statement-1-referral-chronic-open-angle-glaucoma-and-related-conditions

• https://rms.cornwall.nhs.uk/rms/primary_care_clinical_referral_criteria/primary_care_clinical_referral_criteria/opthamology/glaucoma