Glaucoma: symptoms, risk factors and treatment

Glaucoma is not a single disease but a group of eye conditions with one thing in common: the optic nerve is gradually damaged. What makes it so treacherous is that you usually feel nothing for a long time. The Swiss Society of Ophthalmology (SOG) counts glaucoma among the main causes of blindness in people over 60, in Switzerland as elsewhere. But it also points out that glaucoma detected early can be treated successfully and stabilised for decades.

What happens inside the eye

The optic nerve is made up of more than a million fine nerve fibres that carry visual information from the eye to the brain. When fibres die, blind spots appear in your field of vision, as the American Academy of Ophthalmology (AAO) explains.

Eye pressure plays a key role. The eye constantly produces aqueous humour, a clear fluid that drains away through the so-called drainage angle. If less fluid drains away than is produced, the pressure rises. The SOG and the AAO give a normal range of roughly 10 to 20 millimetres of mercury (mmHg).

Pressure alone does not tell the whole story, though:

• Some people have raised readings but never develop glaucoma. This is called ocular hypertension; because the risk is higher, the eye is monitored more closely.
• In normal-tension glaucoma, the optic nerve is damaged even though the measured pressure is within the normal range. According to the SOG, reduced blood flow to the optic nerve probably contributes, for example in people with cardiovascular disease or low blood pressure.

The US National Eye Institute (NEI) sums it up: what is normal pressure for one person may already be too high for another.

Why it goes unnoticed for so long

According to the SOG, the first defects usually appear in the mid-periphery of the visual field; the NEI notes that the part closest to the nose is often affected. Because this happens slowly and sharp central vision is preserved for a long time, it barely registers in everyday life. Only at an advanced stage do the gaps move towards the centre. The AAO and the NEI estimate that around half of people with glaucoma do not know they have it. According to the SOG, advanced visual field loss can even mean that you no longer meet the requirements for driving.

A meta-analysis by Tham and colleagues (2014), which pooled 50 population-based studies, found a global prevalence of 3.54 per cent among people aged 40 to 80. The researchers estimated 64.3 million people with glaucoma in 2013 and projected 111.8 million for 2040. The World Health Organization (WHO) puts the number of people with vision impairment or blindness caused by glaucoma at around 7.7 million. In high-income countries such as Switzerland, glaucoma and macular degeneration account for a comparatively large share of sight loss, according to the WHO.

Who is at higher risk

Anyone can develop glaucoma, including younger people. The SOG, AAO and NEI list the following risk factors, among others:

• Age: according to the SOG, the risk rises from the age of 40.
• Family: glaucoma runs in families. The NEI advises people with glaucoma to encourage their relatives to get checked.
• High myopia: the SOG names short-sightedness of more than –5 dioptres. Our article why myopia is on the rise explains what lies behind the global increase.
• Ancestry: in Tham’s meta-analysis, people of African ancestry had around 2.8 times the odds of open-angle glaucoma compared with people of European ancestry. Angle-closure glaucoma was more prevalent in Asia than in other regions.
• Cortisone (steroids): it can raise eye pressure in some people. If you take steroid medicines over a longer period, the SOG therefore advises having your eye pressure checked regularly.
• Other factors: thin corneas, previous eye injuries, diabetes, high blood pressure or migraine (AAO), and according to the SOG also smoking and sleep apnoea.

Having several of these factors increases the risk further.

Eye pressure: the factor you can influence

Your age and genes are fixed, but eye pressure can be lowered with treatment – which is why eye drops, laser and surgery all target it. The Early Manifest Glaucoma Trial (EMGT) showed how much this matters: 255 people with early open-angle glaucoma received either laser plus eye drops or no immediate treatment. Treatment halved the risk of the disease progressing, and each additional mmHg of pressure reduction was associated with about a 10 per cent lower risk of progression (Leske and colleagues, 2003).

A single pressure reading is not enough for a diagnosis, however. The SOG and the AAO stress that an assessment of the optic nerve and the drainage angle is part of it, supplemented where glaucoma is suspected by a visual field test and measurements of corneal thickness and the nerve fibre layer. This matters because corneal thickness can distort the pressure reading.

A tip if you have had laser eye surgery: after LASIK or PRK the cornea is thinner and its mechanical properties have changed. According to EyeWiki, the AAO’s professional reference, the true pressure usually stays the same, but common measuring methods can show readings that are too low. In studies, the difference ranged from barely measurable to more than 5 mmHg. So mention any previous procedure at every eye examination.

Emergency: acute angle-closure attack

Angle-closure glaucoma, also called narrow-angle glaucoma, is a special form. Here the iris lies so close to the drainage angle that it can block the outflow. If the angle closes completely, the pressure rises sharply within a short time. Typical warning signs of such an attack include:

• suddenly blurred or worse vision
• severe eye pain
• a red eye
• headache, nausea, vomiting
• coloured rings or halos around lights

If you notice these signs, see an ophthalmologist or go to an emergency department straight away. According to the AAO, angle-closure glaucoma can lead to blindness if it is not treated promptly.

Milder early signs such as blurred vision, halos, or mild headaches or eye pain should also be checked by an ophthalmologist as soon as possible, the AAO advises. According to the SOG, marked long-sightedness can favour angle closure. In angle-closure glaucoma, caution is also needed with medicines that dilate the pupil, such as some antidepressants or anti-nausea drugs. Many cases of angle-closure glaucoma, however, develop gradually and without symptoms.

Treatment: drops, laser, surgery

Glaucoma cannot be cured, and lost visual field does not come back – the SOG, AAO and NEI agree on that. Treatment therefore aims to prevent further damage. With timely and adequate treatment, blindness from glaucoma has become rare, according to the SOG.

• Eye drops are usually the first step. They only work if you use them every day. According to the AAO, possible side effects include stinging, red eyes, longer eyelashes or a change in eye colour; some drops can also affect your heartbeat or breathing, especially if you have asthma. So mention any other conditions and medicines you take, and never stop using the drops without talking to your doctor.
• Laser treatments improve drainage: trabeculoplasty for open-angle glaucoma, and a tiny opening in the iris (iridotomy) for angle closure. In the British LiGHT trial with 718 participants who had open-angle glaucoma or raised eye pressure, 74 per cent of those who had selective laser trabeculoplasty as their first treatment still needed no drops to stay at their target pressure after three years.
• Surgery creates a new drainage route, for example through a trabeculectomy or small implants. Because the new channel can scar over, the SOG says close follow-up is needed, especially in the first three months. In eyes with narrow angles, the AAO notes that removing the natural lens – the same procedure used for cataract – can also lower the pressure.

Once you are on treatment, check-ups roughly every three to six months are typical, according to the AAO.

Screening: when to get checked

The SOG recommends a first examination by an ophthalmologist from the age of 40, even if you have no symptoms at all. If you have risk factors, earlier and regular check-ups make sense. The NEI advises people at higher risk to have a comprehensive eye examination every one to two years. How often you personally should go is something your ophthalmologist will decide with you.

At our practice in Wallisellen, eye pressure measurement, nerve fibre analysis and glaucoma diagnostics are part of our ophthalmology services.