Glaucoma: the sight you lose before you notice anything

Glaucoma is a group of conditions in which the optic nerve — the cable carrying sight from the eye to the brain — is progressively damaged. The damage is permanent. Nothing recovers a fibre once it has gone.

What makes glaucoma dangerous is not that it is untreatable. Treated early, most people who develop it keep useful vision for life. What makes it dangerous is how quietly it begins.

Why you do not notice

The common form, primary open-angle glaucoma, takes peripheral vision first. It does so gradually, usually asymmetrically, and the brain is extremely good at covering the loss — it fills the missing region with a plausible guess drawn from the other eye and from the surrounding scene. You do not see a black patch. You see nothing unusual at all.

By the time a person notices, typically describing it as tunnel vision or as repeatedly failing to see things off to one side, a substantial proportion of the optic nerve is already gone. Studies of newly diagnosed patients consistently find that a large share have lost most of the nerve fibres in at least one eye before they ever sought help.

Why this matters particularly here

Glaucoma is more common in people of African descent, tends to begin earlier, and tends to progress faster. It is among the leading causes of irreversible blindness in Nigeria. And because the early stage produces no pain, no redness and no blurring, there is nothing to prompt a visit — which is precisely the problem.

There is also a family pattern. Having a parent or sibling with glaucoma raises your own risk several times over. If someone in your immediate family has been diagnosed, that is a reason to be examined now rather than at some point in the future.

What screening involves

No single test diagnoses glaucoma. The assessment is built from several:

• The optic nerve head, examined directly. Its appearance — the proportion of it that is cupped, the shape of the rim, whether the two eyes differ — is the most informative single observation.
• Intraocular pressure. Raised pressure is the main treatable risk factor, but a normal reading does not clear you: a significant proportion of glaucoma in African and Asian populations occurs at pressures within the normal range.
• Visual field testing, which maps the sensitivity of your peripheral vision and finds the losses your brain has been hiding.
• The drainage angle, which distinguishes open-angle from angle-closure disease. They are managed differently, and one of them can present as an emergency.

The one that is an emergency

Acute angle-closure glaucoma is the exception to everything above. It arrives suddenly: severe pain in and around one eye, marked blurring, coloured haloes around lights, a red eye, often nausea and vomiting. It is frequently mistaken for a migraine or a stomach upset, and it can destroy sight within a day or two.

That combination of symptoms needs to be seen the same day, not next week.

Treatment

Treatment aims to lower the pressure inside the eye and hold it low enough that the nerve stops deteriorating. Usually this begins with eye drops. Laser treatment and surgery are available where drops are insufficient or not tolerated.

The hardest part of the treatment is not medical — it is that the drops must be used every day, indefinitely, for a condition that causes no symptoms. People stop because nothing appears to be happening. Nothing appearing to happen is the treatment working. Sight already lost does not come back when the drops are resumed.

When to be screened

If you are over forty, if glaucoma runs in your family, if you have diabetes, or if you have used steroid medication long-term, you should have a complete examination including the optic nerve and eye pressure, and repeat it annually. If you are Black and over thirty-five, do not wait for forty.

Screening is unremarkable, takes well under an hour, and is available from every licensed optometrist in the chapter's register. It is the cheapest thing you will ever do for your sight.