Glaucoma is a group of eye conditions that damage the optic nerve — the bundle of over a million nerve fibres that carries visual information from the retina to the brain. This damage is most often, though not always, related to abnormally high pressure within the eye, and it is irreversible: vision already lost to glaucoma cannot be restored. This is precisely why glaucoma is treated as one of the most important conditions to catch early, since treatment can effectively halt or substantially slow further damage, but cannot undo what has already occurred.
Glaucoma is often called the “silent thief of sight” because the most common form typically causes no pain and no noticeable symptoms until a significant amount of vision has already been lost — by which point the damage is permanent. It remains one of the leading causes of irreversible blindness worldwide, and is particularly important to understand in Singapore and the wider Asian region, where angle-closure glaucoma, a less common but more acutely dangerous form, occurs considerably more frequently than in Western populations.
How Glaucoma Damages Vision
The eye continuously produces a clear fluid called aqueous humour, which nourishes internal structures and maintains the eye's shape and pressure, before draining away through a mesh-like channel called the trabecular meshwork, located where the iris and cornea meet. Under normal circumstances, fluid production and drainage remain in balance, keeping eye pressure (intraocular pressure, or IOP) within a healthy range.
Glaucoma develops when this balance is disrupted — typically because drainage becomes less efficient, either gradually (as in open-angle glaucoma) or suddenly (as in an acute angle-closure attack) — causing pressure within the eye to rise. Sustained or sharply elevated pressure damages the delicate nerve fibres of the optic nerve, and as fibres are lost, corresponding areas of the visual field are also lost. Glaucoma can also occur, less commonly, with eye pressure that remains within the statistically normal range (normal-tension glaucoma), suggesting that factors beyond pressure alone, such as blood flow to the optic nerve, also play a role.
Types of Glaucoma
- Open-Angle Glaucoma: The most common form, in which the drainage angle remains open but fluid outflow through the trabecular meshwork gradually becomes less efficient. Pressure rises slowly over months to years, and vision loss progresses gradually and painlessly, which is why it is so often missed until it is advanced.
- Acute Angle-Closure Glaucoma: Occurs when the iris blocks the drainage angle, causing a sudden, severe rise in eye pressure over hours. A true ophthalmic emergency, with severe eye pain, redness, blurred vision, haloes around lights, headache, nausea, and vomiting. Considerably more common in Asian populations, including in Singapore, due to anatomical differences in eye structure.
- Normal-Tension Glaucoma: Optic nerve damage and visual field loss occur despite eye pressure remaining within the statistically normal range, suggesting that reduced blood flow to the optic nerve or increased nerve sensitivity to normal pressure may play a role.
- Congenital Glaucoma: A rare condition present from birth or early infancy, affecting roughly 1 in 10,000 babies, caused by abnormal development of the eye's drainage structures. Often noticeable through cloudy corneas, larger-than-normal eyes, and light sensitivity in the affected infant.
- Secondary Glaucoma: Glaucoma with an identifiable underlying cause, such as eye injury, inflammation, certain medications (particularly long-term steroid use), or other eye conditions that disrupt normal fluid drainage.
Why Glaucoma Is Called the “Silent Thief of Sight”
Open-angle glaucoma, the most common form, characteristically damages peripheral (side) vision first, while central vision — the vision used for reading and recognising faces — is typically preserved until late in the disease. Because both eyes usually progress at somewhat different rates, and because the brain is remarkably good at filling in gaps using information from the stronger eye, many people do not notice any visual disturbance at all until the disease is significantly advanced, sometimes only becoming apparent when a substantial portion of the visual field, or even one eye's vision, has already been permanently lost.
This is the central reason regular eye examinations — not waiting for symptoms — are the foundation of glaucoma care. Measuring eye pressure and examining the optic nerve directly can detect glaucoma well before any vision loss would be noticeable to the person experiencing it, at a stage when treatment is most effective at preserving remaining vision.
This matters in a particular way in Singapore and the wider region: angle-closure glaucoma, which behaves very differently from the slow, silent progression of open-angle disease, is meaningfully more common here than in Western populations, related to anatomical differences such as shorter eye length and shallower anterior chambers, which are more prevalent among Asian, and particularly Chinese, populations. This is why local screening guidance places specific emphasis on angle assessment, not just pressure measurement, particularly in older adults and in women, who are also at higher risk of angle-closure glaucoma.
Symptoms of Glaucoma
Open-angle glaucoma
- Typically no symptoms at all in the early and even moderate stages
- Gradual loss of peripheral (side) vision, often not consciously noticed until significant
- In advanced disease, “tunnel vision” as the visual field continues to narrow
Acute angle-closure glaucoma
- Sudden, severe eye pain
- Redness of the eye
- Blurred vision
- Haloes or rainbow-coloured rings around lights
- Severe headache
- Nausea and vomiting
Risk Factors for Glaucoma
- Elevated intraocular pressure: The single strongest risk factor, though glaucoma can occur without it
- Age 50 and older
- Family history of glaucoma
- Ethnicity: Open-angle glaucoma is more common and often more severe in people of African descent; angle-closure glaucoma is more common in people of Asian descent
- Underlying medical conditions, including diabetes, migraines, high blood pressure, and sickle cell anaemia
- Extreme short-sightedness (myopia) or long-sightedness (hyperopia)
- Previous eye injury
- Long-term corticosteroid use
- Thin central corneal thickness
How Glaucoma is Diagnosed
Because glaucoma often causes no early symptoms, diagnosis relies on a structured set of eye examination tests, generally performed together rather than in isolation, to build a complete picture of eye pressure, optic nerve health, and visual function.
- Tonometry: Measures intraocular pressure, most commonly by gently applying pressure to the surface of a numbed eye. A single reading can vary, so pressure is often checked at more than one visit or time of day.
- Ophthalmoscopy: Ophthalmoscopy Direct examination of the optic nerve using a magnifying lens, assessing its appearance for the characteristic thinning and cupping associated with glaucoma damage.
- Perimetry (Visual Field Test): Maps out the full extent of a person's vision, including peripheral vision, to detect and monitor the pattern of vision loss characteristic of glaucoma. It is often the most sensitive way to detect functional damage.
- Pachymetry: Pachymetry Measures corneal thickness, which affects how accurately tonometry readings reflect true eye pressure, and is itself an independent risk factor when thin.
- Gonioscopy: Uses a special mirrored lens to directly examine the drainage angle of the eye, distinguishing open-angle from angle-closure glaucoma — a distinction that is central to choosing the right treatment.
- Optical Coherence Tomography (OCT): Provides detailed, high-resolution imaging of the optic nerve and the surrounding nerve fibre layer, able to detect subtle structural changes, sometimes before they become apparent on visual field testing.
Protecting Your Vision
- Attend regular eye examinations, particularly from age 50 onward, or earlier if you have risk factors. This is the single most effective way to catch glaucoma before it causes noticeable vision loss
- Know your family's eye health history, since glaucoma has a strong hereditary component, and share this with your eye doctor
- Wear appropriate eye protection during sports or when using power tools, since significant eye injury is a recognised cause of secondary glaucoma
- If prescribed glaucoma eye drops, take them exactly as directed and every day. Inconsistent use is one of the most common reasons treatment fails to control eye pressure
- If you are of Asian or Chinese descent, or have a family history of angle-closure glaucoma, ask specifically about angle assessment during your eye examination
- Manage related health conditions, including diabetes and high blood pressure, as part of overall eye health
