Understanding Glaucoma
Glaucoma is one of the leading causes of irreversible vision loss worldwide. However, with early detection and appropriate treatment, it is possible to control the disease and preserve vision in most cases. This guide explains what glaucoma is, how it is detected, and what you can do about it.
This information is for educational purposes. It does not replace a clinical assessment by your ophthalmologist.
What is glaucoma
Glaucoma is a group of eye diseases that damage the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. When the optic nerve is damaged, the visual field gradually narrows, usually starting with peripheral (side) vision.
In most cases, this damage is related to elevated intraocular pressure, although glaucoma can also develop with normal pressure levels. This is why a complete evaluation is essential for an accurate diagnosis.
The role of the optic nerve
The optic nerve is formed by over a million nerve fibers that carry visual signals to the brain. In glaucoma, these fibers are progressively lost. Once they are damaged, they cannot be regenerated.
This is why early detection is so important: the goal of treatment is to prevent further loss, not to recover vision that has already been lost.
Understanding glaucoma
How glaucoma damages the optic nerve
A healthy optic nerve
The optic nerve is made up of around one million fibers. Each carries a small part of what you see from the eye to the brain.
When all of them work, the complete image reaches the brain.
Treatment does not repair what has been lost. Its aim is to protect the remaining fibers.
Why does it progress without symptoms?
The brain is remarkably good at compensating for early visual field loss. Because glaucoma typically affects peripheral vision first, most patients do not notice any change until the disease is advanced.
This is why glaucoma is often called the "silent thief of sight." Regular eye examinations are the only reliable way to detect it early.
How glaucoma affects the visual field
New · Interactive model
Glaucoma, in 3D
A two-minute visual journey: from the healthy eye to glaucoma, and from glaucoma to laser and surgery.
View the 3D journeyIntraocular pressure and glaucoma
Intraocular pressure (IOP) is one of the main risk factors for glaucoma and the only one that can currently be modified with treatment. However, having high IOP does not automatically mean you have glaucoma, and some patients develop glaucoma with statistically normal pressures.
This is why diagnosis cannot rely on pressure measurement alone. A comprehensive evaluation of the optic nerve and visual function is necessary.
How is glaucoma diagnosed?
Three pillars that support one another
No single test diagnoses glaucoma on its own. The diagnosis comes from combining three types of information: the pressure the nerve is under, its structure, and the vision it produces.
Glaucoma diagnosis
A comprehensive assessment, not an isolated number
Pressure
How much pressure is the nerve under?
- TonometryMeasures intraocular pressure. It matters, but on its own it is not enough to make a diagnosis.
- Adjusts the readingPachymetryMeasures corneal thickness, a factor that influences the accuracy of the pressure reading.
Structure
Is there damage to the optic nerve fibers?
- Optic nerve examinationDirect assessment of the optic disc through the microscope or using fundus photographs.
- Optical coherence tomography (OCT)A scan that measures the thickness of the nerve fiber layer. It detects damage before any symptoms appear.
Function
How much vision has already been lost?
- Visual field test (perimetry)A map of visual field sensitivity. It identifies areas of loss, including those the patient is not yet aware of.
These tests are repeated periodically. In glaucoma what matters is not only the result on a given day, but how it changes over time: management is a long-term process.
Available treatments
Different options, one objective
Glaucoma has no cure, but its risk of progression can be reduced. Observation, eye drops, SLT and surgery are considered according to the type and severity of glaucoma, target pressure, anatomy, previous treatment, adherence and other individual factors.
The goal is always the same: lowering intraocular pressure to reduce the risk of further nerve damage. There is no single treatment sequence that applies to every eye.
- A
Eye drops
WhenWhen medication is the most appropriate initial or additional option.
One or more medicines can reduce pressure. Their effect, tolerance and correct use are reviewed over time; adherence matters, but progression can still occur and must be monitored.
- B
Laser (SLT)
WhenAs an initial option in selected open-angle glaucoma or ocular hypertension, or later when additional pressure reduction is needed.
An outpatient procedure that acts on the trabecular meshwork. Its effect varies and can diminish with time; some patients still need medication or repeat treatment.
- C
Surgery
WhenIf a greater or more stable pressure reduction is needed, or the disease keeps progressing.
This includes angle-based procedures, drainage devices and filtering surgery. MIGS may be useful when a modest reduction is sought in selected eyes, whereas more advanced or rapidly progressing disease may require a different approach.
See the surgery guide
The options are not a compulsory ladder. After reviewing pressure, optic-nerve damage, rate of progression, anatomy, other eye conditions and your circumstances, the plan is selected and revised over time.
What can you do
- ✓Attend all scheduled follow-up appointments, even if you feel fine
- ✓Use your prescribed eye drops every day, at the recommended times
- ✓Report any side effects from your medication so the treatment can be adjusted
- ✓If you have a family history of glaucoma, inform your ophthalmologist
- ✓Do not stop or modify your treatment without consulting your doctor
Glaucoma management is a long-term commitment. Consistency with treatment and follow-up is the most important factor in preserving your vision.
When to seek urgent care
Although most forms of glaucoma progress slowly, some situations require immediate attention:
- Sudden, severe eye pain accompanied by nausea or vomiting
- Abrupt loss of vision in one or both eyes
- Seeing colored halos around lights, especially with eye pain
- Intense redness of the eye with blurred vision
These symptoms may indicate an acute angle-closure crisis, which is a medical emergency. Seek immediate attention at the nearest emergency department.
Frequently asked questions
Authorship, medical review and sources
- Author and medical reviewer
- Dr. Francisco Javier Abellán Martínez
- Ophthalmologist · Medical registration no. 282880215
- The same specialist currently authors and medically reviews the content; this is not presented as an independent external review.
- Last medically reviewed
Sources consulted (3)
- Terminology and Guidelines for Glaucoma, 6th edition (Opens in a new tab)European Glaucoma Society
- Glaucoma: diagnosis and management (NG81) (Opens in a new tab)National Institute for Health and Care Excellence (NICE)
- Patient information booklets (Opens in a new tab)The Royal College of Ophthalmologists
General educational content. It does not replace an individual assessment, diagnosis or personalised instructions from your healthcare team.
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