Why a family history of glaucoma matters

Glaucoma is a group of conditions that damage the optic nerve, usually slowly and usually because the pressure inside the eye is higher than the nerve can tolerate. It is one of the leading causes of irreversible sight loss in the UK, and the reason it catches people out is simple: the early stages rarely give any warning. Peripheral vision fades first, and the brain quietly fills in the gaps, so nothing feels wrong until a good deal of nerve tissue has already gone.

Because of that, knowing your family history is genuinely useful. It cannot tell you for certain whether you will develop glaucoma, but it can tell you to start looking earlier, and earlier detection is the single most effective thing you can do. Glaucoma that is found and treated in good time can usually be slowed to the point where it never threatens your day-to-day sight.

What the genetics actually mean

The most common form, primary open-angle glaucoma, is polygenic. That means it comes from the combined effect of many small gene variations, layered on top of age, eye pressure and other risk factors, rather than one single "glaucoma gene" that is passed down. There are rare exceptions. Variations in the myocilin gene can cause an early-onset open-angle glaucoma that clusters strongly in families, often appearing in the thirties or forties, and CYP1B1 is linked to glaucoma presenting in infancy. If a relative was diagnosed unusually young, the inherited pattern tends to be stronger and worth taking more seriously across the wider family.

Some useful numbers, with the caveat that estimates vary between studies:

• Having a first-degree relative (parent, brother, sister or child) with glaucoma raises your risk roughly four to nine times above the general population.
• Brothers and sisters of someone with open-angle glaucoma have a lifetime risk of around 10%, compared with about 2–3% in the general population.
• Family history matters too in angle-closure glaucoma, which is more common in people of East Asian and South Asian descent, and in pseudoexfoliative glaucoma, where genetic variation plays a clear part.
• Most people with a family history still never develop sight loss, provided they are monitored.

Who should be screened, and when

In the UK, adults aged 40 or over who have a first-degree relative with glaucoma are entitled to a free NHS sight test. The entitlement is not automatic, so say clearly at the appointment why you qualify — the optometrist needs to record it.

A sensible rule of thumb for timing is to begin screening about ten years before the age at which your relative was diagnosed, or from age 40, whichever comes first. If your mother was diagnosed at 55, start at 45. If a sibling was diagnosed at 38, start now.

A proper glaucoma-focused assessment usually includes:

• Eye pressure measurement (tonometry), ideally at different times of day
• Examination of the optic nerve, often with a photograph for comparison over time
• A visual field test, which maps your peripheral vision
• A scan of the nerve fibre layer or retinal nerve cells (OCT)
• Gonioscopy, to check whether the drainage angle is narrow or open

Most people with a family history are reviewed every one to two years. Eye pressure can be normal on the day of a single test and still be causing damage, which is why the other checks matter and why a one-off visit is not enough.

How to talk with relatives

Family conversations about health can be awkward, but they are often the moment someone gets diagnosed early. A few things help:

• Be specific. Name the type if you know it — "primary open-angle glaucoma" rather than just "eye problems" — along with who has it and roughly when they were diagnosed.
• Frame it as screening, not blame. Nobody did anything wrong, and nothing can be undone by worrying. What can be changed is when the first test happens.
• Mention the practical bit. Adults over 40 with a first-degree relative are entitled to a free NHS sight test, which removes a common reason for putting it off.
• Make it easy. Offer to book together or send a reminder before their birthday month. A short message is enough — you do not need a long explanation.
• Respect reluctance. Some people find eye tests distressing. Reassure them that the tests are quick and painless, and that the most common outcome is simply being told you are fine and to come back in a year.

Other factors that stack on top of genetics

Genes rarely act alone. Risk rises with age, particularly after 60, though people of African or Caribbean heritage tend to develop glaucoma earlier and more aggressively, so screening may be advised from 40. Short-sightedness, diabetes, high blood pressure, migraine and a previous eye injury all add to the picture. So does long-term steroid use — eye drops, inhalers, creams and tablets can all raise eye pressure in susceptible people, so mention any regular steroid use to your optometrist or GP. If you have narrow drainage angles, certain medications can also trigger an acute attack, which is another reason for a proper angle check.

Practical steps you can take now

Ask older relatives directly whether anyone in the family has glaucoma, and write it down. Book a sight test and state your family history at the start of the appointment. Attend follow-ups even when your vision feels perfect, because glaucoma treatment is about protecting the sight you still have. Use prescribed drops consistently and tell your clinician if they sting, are hard to manage, or if you keep forgetting them — there are usually alternatives. Finally, look after general eye health: don't rub your eyes vigorously, wear eye protection for DIY and sport, keep active, and avoid long periods with your head fully inverted if you have narrow angles. Small, steady habits, plus a test every year or two, are what keep most family-linked glaucoma from ever reaching the point of noticeable sight loss.