What Is Glaucoma (Raised Eye Pressure)?

Glaucoma is a chronic eye disease in which raised eye pressure gradually damages the optic nerve and can lead to loss of visual field. It is often called “raised eye pressure”, but the two are not the same: some people carry high pressure for years with no damage, while others develop glaucoma at normal pressure.

The hardest part of the disease is that it causes almost no early symptoms. Loss usually begins in the peripheral field, and a patient can go a long time without noticing it — why glaucoma is often called silent and insidious.

In Istanbul, Op. Dr. Anıl Kaya assesses patients with suspected or diagnosed glaucoma through eye pressure measurement, optic nerve imaging and visual field testing; with regular monitoring, vision loss can be slowed in most patients. If you have concerns, or a family history, you can book an appointment.

Glaucoma usually affects both eyes, though not always at the same rate — one eye can be more advanced while the other shows few findings. Measuring eye pressure (tonometry) takes only seconds and does not hurt; it is part of a routine eye examination, so it can come to light incidentally, even without suspicion of glaucoma.

Glaucoma is not one disease but a group of conditions that damage the optic nerve by different mechanisms. The most common form, open-angle glaucoma, has a drainage angle that looks open, yet fluid outflow slows over the years and the disease progresses silently, without symptoms.

In angle-closure glaucoma, the drainage angle is suddenly or partly blocked by the iris; pressure can rise sharply within hours, presenting with severe eye pain, blurred vision, haloes around lights and nausea — a genuine emergency.

Normal-tension glaucoma is a less familiar subtype in which optic nerve damage typical of glaucoma develops even though pressure measures within the standard range; “my pressure is normal, so I can’t have glaucoma” is not always true. Which type is present becomes clear only once pressure, the drainage angle and the optic nerve have all been assessed together.

This is not just an academic label — it decides how often a patient is reviewed, which treatment is tried first, and whether the situation is urgent. A preventive laser may be considered for an eye at risk of angle closure, while drops are almost always the first step in open-angle glaucoma. This is why the type is clarified before any treatment plan is built.

Some patients have more than one mechanism at once — for example, a narrow angle alongside a long-standing, insidious open-angle picture. Such mixed cases are why the type is never settled from a single measurement, but from imaging the drainage angle with a detailed optic nerve examination.

In its early stage, glaucoma rarely causes symptoms, which is why the diagnosis is usually made incidentally, at a routine eye examination.

As it progresses, the most typical symptom is an unnoticed narrowing of the visual field — the peripheral field gradually shrinks, and patients may describe bumping into objects, catching a door edge, missing a stair, or not noticing movement from the side while driving at night.

Noticing this takes time, because the two eyes work together: loss in one is partly covered by the other’s field, and the brain automatically “fills in” the gap. A patient may not become aware of it unless each eye is tested separately — one reason glaucoma is so often found through routine examination rather than symptoms.

Some patients still see well with either eye alone even at an advanced stage, because the other eye compensates; this can be falsely reassuring. This is why people with risk factors are advised to have regular examinations on a set schedule, rather than waiting for symptoms.

Outside this insidious course, angle-closure glaucoma can present with sudden, severe symptoms; because it needs urgent evaluation, we cover it separately below. If you have noticed narrowing, a dark patch or missing area in your visual field, our dedicated page looks at which patterns may relate to glaucoma and which may point elsewhere.

Glaucoma does not occur equally in everyone; some features raise the risk considerably. Age is the most familiar factor — the disease becomes more common after 40 and keeps rising with age, as drainage tissue gradually loses function over the years.

A family history of glaucoma is considered to raise the risk, since the drainage angle and the optic nerve’s sensitivity to pressure are, to some extent, inherited. In eyes with high myopia, a longer-than-average eyeball can affect the optic disc; diabetes and long-term corticosteroid use can each raise pressure through different mechanisms. A thin cornea can make tonometry under-read the true pressure, so risk may surface later than it should, while previous eye trauma can directly damage the drainage angle.

Having one or more of these factors does not mean you have glaucoma — it means a regular eye examination matters more for you. Anyone over 40 with one of these factors is advised to have a comprehensive examination assessing eye pressure and the optic nerve, even with no symptoms at all.

The more risk factors present, the more monitoring matters — someone with both a family history and high myopia deserves closer, more frequent follow-up than someone with neither. That said, carrying a risk factor does not mean glaucoma will develop; it only means the likelihood is above average, so a regular examination is more valuable for you.

We look next, in a visual comparison, at how these risk factors relate to the visual field.

The goal of treatment is to bring eye pressure to target so optic nerve damage slows or stops — current methods cannot restore visual field already lost, which is why early diagnosis and follow-up are decisive.

Treatment proceeds in steps. Eye drops that lower pressure are usually the first option; if the response is not enough, or drops are unsuitable, laser is considered next; and when medication and laser together fall short, or the disease is advanced, surgery is evaluated.

More than one class of drop can be used — a single drop suits some patients, while others need two or more together. Using drops every day, at the right times, is decisive for success; a missed or irregular drop can make it harder to keep pressure at target.

Some patients develop redness, stinging or irritation on the eye surface from drops; a change of drop or formulation can be considered, and it is better to raise this with your doctor than stop on your own. Fixed-combination drops — two active ingredients in one bottle — can make a multi-drop regimen easier to follow. Laser is usually short and day-case, though its effect may not be permanent; surgery covers several techniques, chosen by disease stage and eye structure.

Which step suits a given patient depends on eye pressure, the degree of optic nerve damage, and how fast the disease is progressing. Our glaucoma treatment page covers this in more detail.

Which treatment step suits you depends on several factors together: how high the pressure is, the degree of damage already present in the optic nerve, how fast the disease has progressed at recent visits, age, other health conditions, and whether you are likely to keep up a daily drop routine.

A younger patient is being set up with a plan that will run for years; in an older patient, other health conditions and how practical daily drops are day to day can matter more. In the same way, a single high reading is read differently depending on whether the optic nerve already shows damage.

A patient at an early stage with low progression risk may do well with one drop and regular follow-up, while advanced damage or fast progression may move to laser or surgery sooner. Trouble keeping up drops — forgetfulness, technique difficulty, surface irritation — is also weighed; if drops seem unlikely to be used consistently, laser may be brought forward.

This decision needs clear examination findings first, which is why we recommend a full assessment for every patient with suspected glaucoma.

Once treatment starts, the assessment does not stop: whether the chosen step reaches target pressure is checked at the next review, and the step changes if it needs to. Glaucoma treatment is less a fixed plan than a process adjusted over time, according to examination findings.

Open-angle, angle-closure and normal-tension glaucoma all lead to the same outcome — optic nerve damage — but their courses differ widely. Open-angle glaucoma progresses over years without symptoms; a patient often notices something only at an advanced stage, or is diagnosed without noticing anything, at a routine visit.

Angle-closure glaucoma, by contrast, can develop within hours, with severe pain and sudden blurred vision that send the patient to a doctor at once. In normal-tension glaucoma, because pressure sits in the standard range, the disease progresses insidiously like open-angle glaucoma, but diagnosis needs extra care: a “normal” reading alone does not rule glaucoma out.

These different speeds directly affect how often follow-up is needed: a preventive procedure may be brought forward for an eye at risk of angle closure, while open-angle and normal-tension follow-up relies on comparing change over months or years.

Some patients arrive with a vague worry that could point to more than one type — “my pressure wasn’t measured, but I have a headache, is it glaucoma?” comes up often. A headache alone is not specific to glaucoma; but together with sudden blurring, haloes around lights or nausea, the situation becomes urgent. Which type is present, how fast it is moving, and whether urgent evaluation is needed are all clarified by the tests done during a glaucoma examination.

A glaucoma diagnosis is never made from one measurement, but by weighing several tests together. A glaucoma examination measures pressure with tonometry, examines the optic disc clinically and with imaging (OCT), and, where needed, adds a visual field test (perimetry) and a corneal thickness measurement.

Tonometry gives a numerical pressure reading; OCT images the optic nerve fibres at a micron level, catching early damage before it would show clinically. Perimetry maps the location and degree of any visual field loss, while corneal thickness (pachymetry) helps interpret the tonometry result, since a thin or thick cornea can make measured pressure differ from the true value.

Gonioscopy views the structure of the drainage angle directly and is decisive in telling open-angle and angle-closure glaucoma apart. The optic nerve’s appearance is also assessed at every visit; the degree of cupping at the nerve head, and how it changes over time, shows whether damage is progressing.

Weighing these tests together separates glaucoma suspects — raised pressure with no optic nerve damage yet — from those with a confirmed diagnosis.

Diagnosis is often reached by comparing measurements over time rather than from one visit; with borderline readings, your doctor may want to see the findings hold steady before a permanent treatment decision — avoiding both unnecessary treatment and a missed diagnosis.

When one or more of the risk factors above are present together, drainage of fluid from the eye can grow harder over time, and the resulting rise in pressure gradually damages the optic nerve fibres. The optic nerve carries visual information from every point of the eye to the brain along millions of fibres; when some are damaged, the field they carry loses function too.

This damage begins as small, unnoticed gaps in the peripheral field; left untreated, the gaps grow and merge, narrowing the field of vision. At an advanced stage only a narrow central field may remain — tunnel vision — and central acuity can stay preserved for a while, so reading or recognising faces may still seem fine; what is really lost is noticing what is around you.

This does not progress at the same speed in everyone — some eyes change very slowly, others faster. What mainly decides the speed is how well, and how consistently, pressure is controlled with treatment; sticking with treatment matters as much as knowing your risk factors.

The comparison below sets these two situations side by side in simplified form, then summarises the risk factors by frequency.

Once treatment begins, how often you are seen varies by patient; your doctor sets the interval according to whether pressure is staying at target, how fast any damage is progressing, and how you are responding.

Newly diagnosed patients, or those whose treatment has not settled, may be seen more often; once pressure is at target and findings are stable, the interval can lengthen. Visual field testing (perimetry) and OCT are usually repeated at set intervals to compare change.

For patients using drops, these visits are also a chance to check how well the routine is being kept up and to look for side effects such as surface irritation. Keeping every appointment stops a pressure rise going unnoticed for longer than it should.

Some patients, once pressure is at target and feeling well, see follow-up as unnecessary; but normal pressure only shows treatment is working, not that the disease is over. If follow-up stops, pressure can rise again unnoticed, often only surfacing at the next check — so keep the interval your doctor has set unless they change it.

Postponing a check-up for travel, work or forgetting is common; rebooking soon, rather than skipping it, keeps any gap in follow-up to a minimum.

Knowing these differences between the types of glaucoma matters both for making sense of your own situation and for anticipating how often follow-up is likely to be needed.

Open-angle glaucoma is the most common type, which is why it comes to mind first when people hear “glaucoma”; it is generally followed with regular, longer-interval checks. Angle-closure glaucoma is less common but can be fast and dramatic, so it must not be missed — if an earlier exam found a narrow angle, a preventive procedure may be considered before a crisis develops. Normal-tension glaucoma needs more care at diagnosis, though its treatment broadly follows the open-angle path.

In practice, this means that in open-angle and normal-tension glaucoma, patients are largely responsible for keeping their own check-up schedule, while for someone at risk of angle closure, responsibility shifts more towards recognising symptoms and acting quickly. The table below summarises the general tendency of the three types for symptoms and urgency; the exact type and urgency for any individual is set by examination findings.

In glaucoma, treatment aims not to “improve” vision but to preserve what is there — field already lost cannot be recovered with today’s methods. Left untreated, damage progresses: small peripheral gaps grow and merge, until very little field may remain outside central vision.

Because this is usually slow, a patient may not notice until a real loss shows up in daily life — why glaucoma is sometimes called the silent thief of sight. With early diagnosis and regular follow-up, progression can be slowed or stopped in most patients.

At an advanced stage, daily difficulties can include noticing hazards from the side too late while driving, struggling to find your way in crowded places, or hesitating to move at dusk. These appear at a different pace for each person, so “how far will mine progress” can only be answered by comparing examination findings over time.

Visual field loss already caused by glaucoma cannot be reversed by medication, laser or surgery; success is measured not by “improving vision” but by “preserving what remains for as long as possible.” This distinction helps patients stay committed to treatment and follow-up.

If you have noticed narrowing, a dark patch, or a sense of missing area in your own visual field, we cover it on a separate page.

In angle-closure glaucoma, pressure can rise sharply within hours; unlike open-angle glaucoma, it announces itself with sudden, obvious symptoms and needs emergency evaluation.

Symptoms calling for urgent assessment include sudden, severe eye or head pain, sudden blurring, coloured haloes around lights, marked redness, and nausea or vomiting. If these appear together, or start suddenly, go to the nearest eye doctor or emergency department — pressure held this high can permanently damage the optic nerve within a short time.

At an emergency visit, the priority is bringing pressure down quickly, using pressure-lowering drops and, if needed, oral or intravenous medication. Once controlled, laser iridotomy — a small opening made in the iris to clear the obstruction to fluid flow — is usually done to prevent a repeat attack, and is normally recommended for the other eye too, since the tendency can affect both.

Certain systemic medicines — some cold and flu remedies, anti-nausea drugs, or psychiatric medication — can trigger a crisis in narrow-angle eyes; anyone with a known narrow angle or tendency towards angle closure should mention this before starting a new medicine. Having had an attack in one eye is a risk sign for the other.

Unlike the common, open-angle type, this cannot be watched at home or managed by waiting; if your symptoms match those above, prompt evaluation matters.

If you have noticed a change in your visual field, have a family history of glaucoma, or were found to have raised eye pressure at a routine exam, book an appointment with Op. Dr. Anıl Kaya through our contact page.