Why can I have glaucoma if my eye pressure is normal?

Glaucoma is one of the leading causes of irreversible vision loss worldwide. It is often associated with high eye pressure, but this association does not always apply. In some people, the optic nerve can deteriorate even when intraocular pressure (IOP) remains within values considered normal.

For this reason, receiving this diagnosis can be confusing: if the pressure “is fine”, why does glaucoma appear? The key is to understand that pressure is an important factor, but not the only one, and that there are other elements, such as the sensitivity of the optic nerve or vascular factors, which may play a role and require a detailed study.

What is glaucoma and how does it affect the optic nerve?

Glaucoma is a neurodegenerative disease that affects the optic nerve, the structure that transmits visual information from the eye to the brain.

We could compare it to an electrical cable: if it deteriorates, the signal is no longer transmitted correctly. In glaucoma, this “cable” becomes progressively damaged, causing a slow loss of the visual field.

Is it always related to eye pressure?

No. Although raised IOP is the main risk factor, it is not the only one.

There is a form called normal-tension glaucoma, in which damage appears with pressure values considered normal, usually between 10 and 21 mmHg.

What is normal-tension glaucoma?

Normal-tension or normotensive glaucoma is a variant of chronic glaucoma in which:

• IOP remains within normal limits.
• However, the optic nerve shows clear signs of damage.
• The visual field shows characteristic alterations.

This occurs because, in some patients, the optic nerve is more vulnerable and can be damaged by pressures that would not cause problems in other people.

Why can the optic nerve be damaged if the pressure is normal?

In normal-tension glaucoma, factors beyond pressure are usually involved. The most relevant are related to the circulation, or perfusion, of the optic nerve and to the individual susceptibility of the nerve itself.

Factors involved

Several factors have been identified that may explain this phenomenon:

Vascular alterations: These reduce blood flow to the optic nerve.

Nocturnal arterial hypotension: This reduces nerve perfusion during sleep.

Migraines or Raynaud’s phenomenon: These are associated with vascular dysfunction.

Genetic predisposition: This may involve greater structural fragility of the nerve.

In these patients, the optic nerve is more sensitive even to pressures considered normal.

How is it diagnosed if the pressure is normal?

This is where the importance of a specialised and complete diagnosis comes into play.

At Clínica Barraquer, we do not rely solely on eye pressure. The study includes:

• OCT (Optical Coherence Tomography) to analyse the fibres of the optic nerve.
• Visual field testing to assess the visual field.
• Clinical evaluation of the optic nerve, including its appearance, cupping, haemorrhages, etc.
• IOP monitoring at different times, as pressure can vary throughout the day.

Early diagnosis is essential, as the damage is irreversible, but we can slow its progression.

If the pressure is normal, why is it treated by lowering it?

This is another common question. Although the pressure is within the “normal” range, lowering it even further can reduce the mechanical stress on the optic nerve.

It is like a floor that is already cracked: even if the weight is “acceptable”, reducing the load helps prevent the crack from progressing.

Treatment may include:

• Pressure-lowering eye drops.
• Laser treatment.
• In selected cases, surgery.

At Barraquer, we assess each case individually to determine the ideal target pressure for each patient.

Who is at greater risk of developing glaucoma with normal tension?

There are certain profiles in which we must be especially vigilant:

People over the age of 60: Greater fragility of the optic nerve.

Family history: An important genetic component.

People with migraine: Vascular association.

Patients with low blood pressure: Possible reduced ocular perfusion.

In these patients, even with normal eye pressure, regular check-ups are recommended.

The importance of follow-up

Glaucoma is silent. It does not hurt and it gives no warning. When obvious symptoms appear, the damage is usually advanced. That is why we insist on a complete ophthalmological examination, especially when risk factors are present.

In summary, it is possible to have glaucoma with normal eye pressure because pressure is an important factor, but not the only one: the sensitivity of the optic nerve, blood circulation and certain individual factors can cause damage even with “correct” values. For this reason, the key lies in a complete diagnosis and specialised follow-up that makes it possible to detect changes in time and slow progression.

Dr Marta Mármol, ophthalmologist at Barraquer Ophthalmology Centre