Glaucoma: eye pressure, the optic nerve, and the three tests that matter

Dr. Swati Goyal · 18 April 2024 · 8 min

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You read that right — just as the body has blood pressure, the eye has a pressure of its own. In glaucoma that pressure damages the optic nerve.

What glaucoma is

The optic nerve is like a cable joining the eye to the brain. Whatever the eye sees, the brain recognises through that cable. In glaucoma the nerve withers slowly — so the eye still sees the image, but the brain can no longer make it out.

Eye pressure — intraocular pressure, or IOP — should sit between 10 and 21 mmHg. Above 21, damage to the nerve can begin.

In its early stages glaucoma has no symptom you could notice yourself. That is exactly why it takes sight quietly — and why testing is the only way to find it.

The main types

There are many forms, but three cover most of what we see.

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  Angle-closure glaucoma — fluid is being made inside the eye but cannot drain out.

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  Open-angle glaucoma — the drainage channel is open, but more fluid is being produced than it can clear.

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  In the third kind the nerve is itself sensitive, and is damaged even at normal pressures.

Who is most at risk

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  Anyone over the age of 50.

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  Anyone with blood pressure, diabetes, heart disease or migraine — in these conditions the optic nerve is more sensitive, and the risk of damage rises.

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  Anyone whose parent or close relative has lost sight to glaucoma.

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  Anyone who injured an eye in childhood, or has had eye surgery before.

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  Anyone with a very high spectacle number, or who has taken steroids over a long period for another illness.

In some cases glaucoma is present from birth.

The three basic tests

1. 1

   Eye pressure, by tonometry. Two ways: non-contact, where a puff of air measures the pressure without touching the eye; and contact, where a lens is placed on the eye to measure it.

2. 2

   Gonioscopy. A special lens is used to study the angle of the eye — the corner where the cornea meets the white, through which fluid drains.

3. 3

   Perimetry. This shows the health of the nerve — how weak it is, in which part of the field, and by how much. It is what we track at every follow-up.

On the basis of these three, the doctor decides whether to start treatment — and if so, how.

Treatment

Glaucoma can be controlled. Eye drops, laser and surgery are all available. Treatment usually begins with drops.

Which molecule suits you depends on several things — the anatomy of your eye, your general build, and any other illness or medicine you are already on.

Glaucoma medicines do carry side effects. Regular follow-up after starting them is essential — to confirm the pressure is coming down as intended, and that nothing troublesome has crept in.

A technique worth learning: punctal occlusion

There is a particular way to put in glaucoma drops, called punctal occlusion.

1. 1

   Pull the lower lid down to make a pocket, and put one drop into it.

2. 2

   Now press gently on the inner corner, near the nose, for about a minute.

This keeps the drop in the eye longer and stops it draining down the nose into the throat. When medicine reaches the throat people often report soreness, a bitter taste and reduced appetite — this avoids that.

Sight already lost to glaucoma does not come back. Treatment protects what remains — which is why catching it early matters more than anything else.

If you fall into any of the risk groups above, have your eyes checked regularly by an eye specialist — do not wait for symptoms.