Glaucoma

What it is

Glaucoma is damage to the optic nerve, the bundle of fibres carrying visual information from the eye to the brain. As those fibres die, the areas of vision they served go with them.

Pressure inside the eye is the main risk factor, and the only one that treatment can change. But pressure and glaucoma are not the same thing, and conflating them causes real confusion. Pressure can be raised without any nerve damage occurring, a situation called ocular hypertension, which is monitored rather than assumed to be glaucoma. Damage can also occur at pressures within the normal range. A normal pressure reading on its own does not rule glaucoma out, which is why an eye examination looks at the optic nerve and the field of vision as well.

The reason it matters: it is silent

This is the single most important thing about glaucoma, and it is what separates it from almost every other eye condition.

The commonest form produces no symptoms whatever in its early and middle stages. No pain, no redness, no blurring, nothing to prompt a visit to anyone. It takes peripheral vision first, and peripheral vision is not something people consciously use or monitor. The brain is also extremely good at filling in missing areas from the other eye and from surrounding context, so gaps go unnoticed.

By the time someone notices a problem, a substantial amount of nerve has usually died, and none of it comes back.

This is why glaucoma dominates the case for routine sight tests in people with nothing wrong. It is the condition that most repays being looked for, because looking is the only way it is found in time.

The slow kind and the sudden kind

Primary open-angle glaucoma is the common one. The drainage channels that let fluid out of the eye become gradually less efficient over years, pressure creeps up, and the nerve is damaged slowly. It usually affects both eyes, often one more than the other. It is the silent form described above.

Acute angle-closure glaucoma is its opposite in every respect. Drainage is blocked suddenly, pressure rises steeply within hours, and it announces itself unmistakably: intense pain in and around the eye, a red eye, blurred vision, rings or haloes around lights, headache, and nausea or vomiting that can be severe enough to send people looking for a stomach explanation. It is a medical emergency and belongs in an accident and emergency department immediately. It is also one of the conditions behind the warnings in the conjunctivitis article, because a painful red eye is where it starts.

Two less common forms complete the picture. Secondary glaucoma arises from another eye condition, such as uveitis or injury. Childhood or congenital glaucoma is rare, caused by an abnormality of the eye's drainage present from birth, and treated surgically.

Who is more likely to get it

Age is the strongest factor, and it is commonest in people in their seventies and eighties. Beyond that:

• having a parent, brother, sister or child with glaucoma
• being of African, Caribbean or Asian origin
• short-sightedness, and for the angle-closure form, long-sightedness
• diabetes

Family history is the one worth acting on, because it comes with an entitlement that many people do not know about. Anyone aged 40 or over who has a parent, sibling or child diagnosed with glaucoma qualifies for a free NHS sight test, as does anyone diagnosed with glaucoma themselves. That is a direct, practical consequence of knowing one's family history, and it is worth asking relatives about.

Whether glaucoma itself can be prevented is unclear. What is not in doubt is that it can be caught early, and that early is the only version of this that goes well.

How it is found

Almost always during a routine sight test, before the person has any complaint.

Several things are checked, and no single one is sufficient on its own. Tonometry measures pressure inside the eye, usually with a puff of air or a contact instrument. Perimetry, the visual field test, maps the sensitivity of peripheral vision and finds gaps the person cannot detect themselves. The optic nerve is examined directly, through a slit lamp or with an optical coherence tomography scan that images the nerve fibre layer in cross-section. Gonioscopy checks whether the drainage angle is open or closed, which determines which type is in play.

Suspected glaucoma is referred to an ophthalmologist, who confirms it and takes over management.

What treatment can and cannot do

The limit is worth stating plainly before the options, because it shapes everything else.

Vision already lost to glaucoma does not come back. Optic nerve fibres do not regenerate, and no treatment restores them. What treatment does is lower the pressure inside the eye, which halts or slows further damage.

Put differently: treatment protects the sight someone still has. That makes early detection worth a great deal and late detection worth much less, and it is why the condition is managed with lifelong monitoring rather than a course of something.

Where sight has already been lost, the practical and financial support described in the low vision article applies, and glaucoma is one of the commoner reasons for registration.

The first treatment has changed

Anyone whose impression of glaucoma treatment is a lifetime of daily drops is working from advice that is now out of date.

Since January 2022, national guidance has recommended selective laser trabeculoplasty, usually shortened to SLT, as the first treatment offered to people newly diagnosed with primary open-angle glaucoma or ocular hypertension. Eye drops became the alternative rather than the default.

SLT is an outpatient procedure taking roughly five to ten minutes per eye. The laser is applied to the drainage meshwork and stimulates the cells there to work more effectively, which lowers pressure. There is no incision.

The change followed a trial of more than seven hundred newly diagnosed people, half treated with SLT and half with drops, followed for three years. Quality of life was much the same in both groups, and so were side effects. But the laser group were more likely to reach their target pressure and less likely to need surgery later, and the approach was more cost-effective.

The practical upshot is that many people treated this way need no drops at all for several years, or fewer than they otherwise would. SLT does not always work, and its effect can wear off, in which case it can be repeated or drops started. It is not suitable for the angle-closure form.

None of this removes choice: drops remain available, and anyone already diagnosed and settled on treatment is unaffected by the change.

Drops, surgery, and the part that gets neglected

Pressure-lowering drops are used between once and four times a day, and they are taken for life. There is no course to finish.

That is where the real difficulty lies, and it is worth being honest about. The drops treat something that produces no symptoms, so they deliver no noticeable benefit — nothing feels better afterwards. Some sting. The result is that they are easy to deprioritise, and stopping is a common reason for glaucoma progressing in someone who is nominally being treated. Anyone finding them difficult, for any reason, is better off saying so at the next appointment than quietly abandoning them, since there are several classes of drop and other options entirely.

Where drops and laser are not enough, surgery can improve drainage. Trabeculectomy is the established operation, and a range of smaller procedures now exists alongside it. Acute angle-closure is treated urgently with medication to bring pressure down, followed by laser treatment to reopen the drainage route.

Whatever the treatment, the monitoring continues. Appointments check whether pressure is controlled and whether the field of vision is holding steady, and they are the mechanism by which treatment gets adjusted before more sight is lost.

Driving

Glaucoma affects the field of vision, which is part of the legal standard for driving, so a diagnosis must be reported to the DVLA — the DVA in Northern Ireland.

That is not the same as losing a licence. Many people with glaucoma continue to drive, and the authority assesses whether the field of vision meets the required standard, usually by means of a specific test. What is not acceptable is leaving them uninformed: failing to declare a condition that affects vision is an offence and invalidates insurance.

The full driving vision standard is set out in the eye tests article.