Glaucoma Screening: What to Expect at Your Eye Exam
Glaucoma Screening: What to Expect at Your Eye Exam
Glaucoma is one of the leading causes of irreversible blindness worldwide — and yet most people with early glaucoma have no symptoms at all. No pain. No blurred vision. No warning. By the time you notice something is wrong, significant and permanent nerve damage has already occurred.
This is why glaucoma screening matters so much. A routine eye exam can detect the earliest signs of glaucoma years before you would ever notice them yourself. If you have been told you need a glaucoma screening, or if you are wondering whether you should ask for one, this guide explains exactly what the process involves, what each test measures, and what your results might mean.
What Is Glaucoma, and Why Is Screening So Important?
Glaucoma is a group of eye conditions that damage the optic nerve — the cable that carries visual information from your eye to your brain. In most cases, this damage is caused by elevated pressure inside the eye (intraocular pressure, or IOP), though a significant number of glaucoma patients have normal-range IOP. This variant, known as normal-tension glaucoma, is particularly common in East Asian populations.
The optic nerve contains over a million nerve fibres. Glaucoma destroys them slowly and silently, starting at the edges of your visual field. Because central vision is preserved until late in the disease, most people lose 30–40% of their nerve fibres before noticing anything amiss.
The good news: glaucoma cannot be cured, but it can be controlled. When caught early, treatment (eye drops, laser, or surgery) can halt progression and preserve functional vision for life. This makes screening — not waiting for symptoms — the only reliable strategy for protecting your sight.
Who Should Be Screened for Glaucoma?
Not everyone needs a glaucoma screening at every eye exam, but certain groups face significantly elevated risk.
High-Risk Groups
Family history is one of the strongest risk factors. If a first-degree relative (parent, sibling) has glaucoma, your lifetime risk is roughly four to nine times higher than average.
Age is the other major driver. The prevalence of primary open-angle glaucoma — the most common form — rises sharply after 40 and accelerates further after 60. Most clinical guidelines recommend baseline screening for all adults over 40.
Ethnicity carries significant weight, particularly in Asia. Studies consistently show that East Asians (Chinese, Japanese, Korean, Vietnamese) have higher rates of normal-tension glaucoma compared to European populations. South Asians and African-descent individuals also face elevated risk. In Singapore, glaucoma is the second leading cause of irreversible blindness, and the Singapore Chinese Eye Study found a glaucoma prevalence of around 3% in the Chinese population over 40 — higher than equivalent European data.
High myopia (short-sightedness above −6 dioptres) substantially increases glaucoma risk, likely because the mechanical tension of an elongated eye places the optic nerve under greater strain. Given Singapore and Southeast Asia's extremely high myopia rates, many young patients are already in an elevated-risk category by the time they reach their thirties.
Previous eye injury or surgery, long-term steroid use (including asthma inhalers and skin creams), and diabetes are also recognised risk factors.
If any of these apply to you, mention them to your optometrist. They will guide how frequently you should be screened.
The Glaucoma Screening Tests Explained
A comprehensive glaucoma assessment is not a single test — it is a combination of measurements that together build a picture of your optic nerve health. Here is what each one involves.
1. Intraocular Pressure (IOP) Measurement — Tonometry
This is usually the first test people associate with glaucoma screening. Tonometry measures the pressure of the fluid inside your eye (aqueous humour). Elevated IOP — typically defined as above 21 mmHg — is a key risk factor.
There are two common methods:
- Non-contact tonometry (the air puff test): A brief puff of air is directed at your eye. It is startling but painless and takes under a second. No eye drops are required.
- Goldmann applanation tonometry: A small probe briefly touches the anaesthetised cornea to measure pressure directly. This is the gold standard in clinical settings and is slightly more accurate. A drop of anaesthetic and orange-tinted fluorescein dye is placed in your eye first; you feel nothing.
Important caveat: IOP alone does not diagnose glaucoma. Many people with IOP above 21 mmHg never develop the disease (ocular hypertension), and a substantial proportion of glaucoma patients have IOP within the normal range. IOP is one data point, not the whole picture.
2. Optic Nerve Head Assessment — Fundoscopy / Slit-Lamp Examination
Your optometrist will examine the optic disc — the point where the optic nerve enters the eye — using a slit-lamp biomicroscope with a special lens, or a direct ophthalmoscope. Dilation drops may be used to enlarge the pupil and improve the view, though modern non-mydriatic cameras can often capture adequate images without dilation.
The examiner looks at the cup-to-disc ratio (CDR): the proportion of the optic disc occupied by the central cup. A larger cup relative to the disc may indicate nerve fibre loss. They also look for asymmetry between the two eyes, disc haemorrhages (a specific glaucoma sign), and irregularities in the neuroretinal rim.
3. Visual Field Testing — Perimetry
Standard automated perimetry (SAP) maps your peripheral vision by asking you to press a button whenever you see a small light flash at various positions across your visual field. You will be tested one eye at a time, in a darkened room, staring at a central fixation point.
The test typically takes 5–10 minutes per eye. It can feel repetitive or tiring, especially if you are doing it for the first time. Reliability indices in the results tell the clinician how consistent your responses were — a poor result does not necessarily mean there is a problem with your eyes; it may simply need to be repeated.
Glaucoma characteristically produces distinctive visual field defects — arcuate scotomas and nasal steps — that correlate with the pattern of optic nerve damage. However, by the time perimetry can reliably detect a defect, roughly 25–35% of nerve fibres have already been lost. This is why structural imaging (OCT, below) has become so important for early detection.
4. Optical Coherence Tomography (OCT)
OCT is now considered essential in any comprehensive glaucoma assessment. It uses low-coherence infrared light to create high-resolution cross-sectional images of the retina, measuring the thickness of the retinal nerve fibre layer (RNFL) and the ganglion cell complex (GCC) around the macula.
The scan is completely non-invasive, takes about 30 seconds per eye, and requires no contact with the eye. You look at a target light inside the machine while it captures images automatically.
OCT can detect thinning of the RNFL before any visual field loss appears — sometimes years earlier. Results are compared against an age-matched normative database, with colour-coded maps (green = normal, yellow = borderline, red = outside normal limits) that make interpretation intuitive.
5. Gonioscopy (if indicated)
Gonioscopy is performed when your clinician needs to examine the drainage angle — the anatomical structure where fluid leaves the eye. It distinguishes open-angle glaucoma (the drainage angle is open but the drainage meshwork is inefficient) from angle-closure glaucoma (the iris blocks the drainage angle, causing acute or chronic pressure rises).
A special mirrored contact lens is placed on the anaesthetised eye. This is not painful, but it may feel unusual. Gonioscopy is not part of every screening; it is performed when the anatomy of your eye suggests angle closure may be possible or when the optic nerve findings warrant closer investigation.
6. Corneal Pachymetry
Central corneal thickness (CCT) is routinely measured because it influences IOP readings. A thin cornea means the true IOP may be higher than the measured value; a thick cornea means IOP may be overestimated. CCT is measured using an ultrasonic probe or optical device touching the anaesthetised cornea for a fraction of a second.
What a Typical Screening Visit Looks Like
Here is a realistic timeline for a first-time comprehensive glaucoma screening at an optometry practice:
| Stage | Test | Approximate Time |
|---|---|---|
| 1 | Intraocular pressure (air puff or applanation) | 2–3 minutes |
| 2 | Optic nerve photography / fundoscopy | 5 minutes |
| 3 | OCT of optic nerve and macula | 5 minutes |
| 4 | Corneal pachymetry | 2 minutes |
| 5 | Visual field test (if indicated) | 10–15 minutes per eye |
| 6 | Gonioscopy (if indicated) | 5 minutes |
| 7 | Review and discussion with optometrist/ophthalmologist | 10 minutes |
| Total | ~30–45 minutes |
You may not need every test at every visit. A routine screen for a low-risk patient might cover only IOP, optic nerve assessment, and OCT — a 15-minute appointment. If anything is borderline, the additional tests follow.
Understanding Your Results
After the assessment, your clinician will typically classify your findings into one of several categories:
Normal / Low risk: IOP within range, healthy optic nerve appearance, normal RNFL thickness, normal visual field (if performed). Recommended: routine screening every 1–2 years after age 40, sooner if risk factors are present.
Glaucoma suspect: One or more measurements are outside the normal range — perhaps elevated IOP, a suspicious-looking disc, or borderline RNFL thinning — but no definitive glaucoma diagnosis is possible. You will be monitored more closely, typically every 6–12 months, to determine whether changes are progressive.
Glaucoma confirmed: Consistent structural damage (optic nerve/RNFL) with corresponding functional loss (visual field defect), or unambiguous progressive change on serial monitoring. Referral to an ophthalmologist for treatment will be recommended.
It is important to understand that a single abnormal result rarely means an immediate diagnosis. Glaucoma is a progressive disease, and most diagnoses are confirmed over multiple visits by demonstrating that change is occurring. Your optometrist will explain what the findings mean in the context of your specific risk profile.
How Often Should You Be Screened?
Frequency of screening depends on your risk level:
- No risk factors, under 40: Every 2–3 years as part of a comprehensive eye exam
- No risk factors, 40–60: Every 1–2 years
- Over 60, or any one major risk factor: Annually
- Glaucoma suspect: Every 6–12 months as directed
- Confirmed glaucoma: Every 3–6 months, or as directed by your ophthalmologist
If you are highly myopic (above −6D) and based in Singapore or another high-myopia region, consider annual screening from age 35 onwards — the combination of myopia prevalence and normal-tension glaucoma risk in East Asian populations makes earlier and more frequent screening prudent.
Finding an Eye Care Professional for Glaucoma Screening
Glaucoma screening can be performed by qualified optometrists equipped with OCT and automated perimetry, or by ophthalmologists. If your optometrist identifies suspicious findings, they will refer you to an ophthalmologist for confirmation and management.
Use the CarrotByte Eye Care Directory to find eye care professionals near you in Singapore and Southeast Asia. The directory includes practices that offer comprehensive eye examinations, making it straightforward to find a clinic equipped for glaucoma assessment.
Why CarrotByte
For optometrists managing glaucoma suspects and confirmed glaucoma patients, consistent follow-up is critical. CarrotByte's patient recall system helps practices automatically schedule and remind patients about their next screening appointment — reducing the risk that a high-risk patient falls through the cracks between their six-month visits.
Start a free trial at app.carrotbyte.io and see how CarrotByte helps you keep your at-risk patients on schedule.