Glaucoma

Glaucoma is the slow loss of the optic nerve, the cable that carries the picture from the eye to the brain. Its fibres die off one at a time and in silence, so the disease can run for years without announcing itself: the person reads the bottom line of the chart as well as ever and hears about the diagnosis at the appointment they booked to change their glasses. The essential point is this: no treatment brings back the fibres that have gone, but holding the disease at the level of sight someone has today is almost always achievable. All the value, then, lies in how early it is found.

Why it is spotted so late

Sight narrows from the edges, not from the middle. The gaps appear in the side field, exactly where we neither look directly nor read. The brain does not show those gaps as black patches; it fills the scene in from whatever surrounds them. On top of that the two eyes are rarely affected equally, and the better one covers for the worse for a long time, so with both eyes open there is no defect at all.

The upshot is that suspicion arrives once more than half the fibres have gone. And it does not arrive as blurring, but as small clumsinesses that get blamed on age and tiredness:

• you catch your shoulder on door frames and knock cups off the table more than you used to;
• changing lanes has become awkward, and the car in the next lane appears out of nowhere;
• on steps and kerbs you find yourself looking down and treading carefully;
• at dusk, or walking from bright sunshine into a dim hallway, the eye takes far longer to settle than it once did.

If any of that sounds familiar, do not put the eye test off — but there is no need to panic either, because cataract and ordinary age-related long sight do the same. Only instruments can tell them apart.

The attack where hours count

One form behaves the other way round and collapses within hours: the drainage shuts off all at once, the pressure inside the eye trebles, and it hurts a great deal. The signs are these:

• severe pain in and around the eye, often spreading into the temple;
• the eye reddens and vision clouds suddenly, as if through misted glass;
• coloured haloes appear around street lamps and light bulbs;
• nausea and vomiting;
• the eye feels hard to the touch, and the pupil stays wide and does not shrink in the light.

The danger lies not only in the pressure but in what the attack gets mistaken for. Because of the vomiting and the headache it is regularly treated at home as a migraine or a stomach upset, and that costs exactly the night that decides the outcome: if the pressure is not brought down within a few hours, the nerve is lost for good.

This is an emergency. You need to reach an emergency department the same hour, ideally one with an eye service on call — not in the morning, not after the weekend. Nobody drives in that state, so ask to be taken; if there is no way of getting there, call an ambulance, which across Europe is the single number 112. Take the list of everything you are taking with you.

The attack tends to strike in the evening, in low light, after a fright, or after drops that widen the pupil. Some tablets can set it off too — for travel sickness, allergy, incontinence, cramps, and a number of antidepressants. That is what the leaflet means by "not to be used in closed-angle glaucoma". If you have been given that diagnosis, show your medicines list both to the eye specialist and to whoever is prescribing something new.

What damages the nerve

The eye continuously makes a clear fluid that bathes the lens and leaves through a drainage mesh in the angle between the iris and the cornea. When less leaves than arrives, pressure builds and squeezes the fibres at the point where the nerve exits the eye. How exactly the drainage has failed also decides the treatment:

• open-angle, much the commonest: the angle is clear, but the mesh filters worse and worse, like a clogging filter. It runs for years and without symptoms;
• closed-angle: the root of the iris blocks the angle. It can close slowly, or produce the attack described above;
• normal-tension: the readings come back fine and the nerve is lost anyway, because it turns out to be sensitive to a pressure others tolerate, and because its blood supply plays a part. It is found only by looking at the nerve and the visual field;
• secondary, following something else: an injury, long-standing inflammation inside the eye, uncontrolled diabetes, a lens that has shifted. Steroid glaucoma deserves its own mention: cortisone drops and ointments used for months "for the redness" without supervision push the pressure up in a proportion of people;
• congenital, rare and seen in babies. It gives itself away by watering, dislike of light and unusually large, "beautiful" eyes; those eyes are for showing to a doctor rather than admiring.

Risk climbs with every decade after forty. It is higher if a parent, brother or sister had glaucoma; if you are of African descent, because in that group the open-angle form starts earlier and runs a harder course; and if your ancestry is East Asian, where closed-angle predominates. High short sight, long sight in a small eye, diabetes, long courses of steroids and an old blow to the eye all add to it.

How it is found

Measuring the pressure is not enough, and this is the commonest misunderstanding about glaucoma: a normal reading does not rule the diagnosis out, and a high one on its own does not make it. Several things are looked at together:

• the pressure inside the eye, corrected for corneal thickness — on a thick cornea the instrument reads high, on a thin one low;
• the optic nerve itself, which the doctor views at the back of the eye through the pupil to judge how far the disc has been hollowed out;
• the visual field on a perimeter: you press a button whenever you catch a flash off to the side. That is how the losses you cannot feel show up;
• the thickness of the nerve fibre layer on a scan, which thins before the field of vision deteriorates;
• the drainage angle through a special lens, which decides whether laser is appropriate and whether pupil-widening drops are dangerous for you.

A regular eye check is the only way to catch this in time. An adult is well served by having the eyes looked at every one to two years, and from forty onwards, or with risk factors, as often as the doctor advises; every country organises that check differently, in some it is done by an ophthalmologist and in others by an optometrist. And one thing almost nobody remembers: if glaucoma has been found in you, your adult children and your brothers and sisters should be checked. In first-degree relatives the risk is several times higher, and they are better off starting earlier.

What keeps the sight

The aim is single: bring the pressure down far enough for the fibres to stop dying. That target figure is set eye by eye, according to how far the damage has gone. Glaucoma cannot be cured, but it can usually be halted.

• Drops. Some cut down how much fluid is made, others help it leave. The main classes are prostaglandin analogues, beta-blockers, carbonic anhydrase inhibitors and alpha agonists, and they are often combined in a single bottle. The doctor chooses them, and swapping to "something similar" on your own does not work here.
• Laser. A short and near-painless procedure. With an open angle the laser unclogs the drainage mesh, and treatment increasingly starts there rather than with drops. With a closed angle a tiny opening is made in the iris so the fluid can bypass the block — that is both the treatment and the protection for the other eye against an attack.
• Surgery. When pressure stays high, a new route out is created, either fashioned in the tissues of the eye or provided by a microscopic implanted drain. Some of these are done at the same time as cataract surgery.

There is never quite time in the clinic to say everything about drops. After putting them in, close the eye and press the inner corner with a finger for a minute: the medicine then stays in the eye instead of running down the nose into the bloodstream. Do tell the doctor if you have asthma, serious breathlessness or a slow pulse, because beta-blockers in a drop do not act on the eye alone. They may sting at first, the eye reddens, and in some people the eyelid skin darkens and the lashes grow longer; none of that is a reason to stop, but all of it is worth mentioning.

And the main thing. Drops work for as long as they are put in — every day, for years, including on the days when everything looks perfectly fine. Their benefit cannot be felt, because they do not improve sight, they stop it going. That is why glaucoma more often blinds the person who stopped using the drops and missed the follow-up than the person with nothing to treat it with.

Living with it

Found in time, most people see well enough for the rest of their lives to read, drive and work. The diagnosis changes the routine more than the eyesight: drops morning and evening, a doctor every few months, a field test once a year.

Tie the drops to something you already do daily, set an alarm, and keep a spare bottle wherever you sleep. If your hands shake or you struggle to aim, say so: there are holders that clip onto the bottle, there are preservative-free single-dose forms, and sometimes moving to laser is simply easier. Ask separately about driving, since the visual field standards for drivers differ from country to country and it is better to learn them beforehand than at a medical.

For anyone who has already lost sight, plain measures help: bright and even light at home, contrasting tape on the edge of each step, no loose rugs or cables underfoot, large print, magnifiers, audiobooks. Anxiety and low mood with this diagnosis are ordinary, and they too belong in the conversation with the doctor rather than being endured.

Online consultation

Everything that does not need instruments can be dealt with remotely, and with glaucoma there is plenty of it. The doctor goes through the report and the pressure figures, explains what your visual field means and why these particular drops were chosen, checks your instillation technique, helps work out whether a new complaint comes from the treatment, and goes down your medicines list for anything risky with a narrow angle. It is also a convenient way to decide whether your children or your brothers and sisters should be examined and where they should start. Pressure cannot be measured, the nerve cannot be seen and a field test cannot be run through a screen, so an online appointment adds to a face-to-face examination rather than replacing it. The signs of an attack listed above are not discussed remotely at all — with those you go straight to hospital.

This material is for information only and does not replace medical advice.