What is glaucoma?

Glaucoma is the name for a group of eye conditions that damage the optic nerve. The optic nerve carries visual information from the eye to the brain. If it is damaged, it can lead to sight loss and, if left untreated, blindness.

In most cases glaucoma is linked to raised pressure inside the eye. Diagnosis is not always straightforward, and several tests are usually needed to confirm whether damage to the optic nerve has occurred and why.

Urgent: sudden severe eye pain with blurred vision, haloes around lights, a red eye, headache, and feeling sick are signs of acute angle closure. This is an emergency. Go to an emergency department the same day.

Why symptoms appear so late

Glaucoma usually affects your peripheral vision first, the vision at the edges. Your central vision, which you use for reading and recognising faces, stays good until much later.

Because of this, most people notice nothing in the early stages. One eye often compensates for the other. By the time a change is obvious, a significant amount of optic nerve has usually been lost.

Sight that has already been lost to glaucoma cannot be restored. However, with treatment, the damage can be slowed or stopped. The majority of people diagnosed and treated early will keep useful sight for life.

Eye pressure explained

The eye continually produces a clear fluid called aqueous. This fluid nourishes the front of the eye and then drains away through a filter called the trabecular meshwork, in the angle where the iris meets the cornea.

The balance between how much fluid is made and how much drains away sets the pressure inside the eye. If drainage becomes restricted, the pressure rises. Over time, raised pressure can damage the optic nerve.

Two points often surprise people.

Glaucoma can occur at normal pressure. Some people develop optic nerve damage even though their eye pressure is in the normal range. This is called normal tension glaucoma.

Raised pressure does not always mean glaucoma. Some people have higher than normal pressure with a healthy optic nerve. This is called ocular hypertension, and it is monitored rather than automatically treated.

The main types

Primary open angle glaucoma is the most common type. The drainage angle is open, but the filter becomes less efficient over time. It develops slowly and painlessly.

Angle closure glaucoma occurs when the iris blocks the drainage angle. It can develop gradually, or come on suddenly as an acute attack.

Secondary glaucoma is raised pressure caused by something else, such as inflammation, injury, diabetes, or long-term steroid use.

Developmental glaucoma affects babies and young children. It is rare and is managed in specialist paediatric centres.

Who is at risk?

• Age. Glaucoma is uncommon before 40 and becomes more common with age.
• Family history. If you have glaucoma, your brothers, sisters and children are at higher risk. Tell them, so they can be tested.
• Ethnicity. People of African and Caribbean origin are at higher risk of open angle glaucoma. People of East Asian origin are at higher risk of angle closure.
• Short sight increases the risk of open angle glaucoma. Long sight increases the risk of angle closure.
• Steroid use, including inhalers, nasal sprays, creams and drops, used long term.
• Previous eye injury or inflammation.
• Diabetes, and high or low blood pressure.

What the assessment involves

Several tests are used together to build a picture.

Eye pressure is measured, ideally by applanation rather than the air-puff method.

Corneal thickness is measured. A thick cornea can make the pressure read falsely high, and a thin cornea can make it read falsely low. Thin corneas are also a risk factor in their own right.

The optic nerve is examined for its shape and for any difference between the two eyes.

Gonioscopy uses a mirrored lens to look directly into the drainage angle and establish whether it is open or narrow. This determines which treatments are suitable.

An OCT scan measures the thickness of the nerve fibre layer and can detect loss before it shows up on a visual field test.

A visual field test maps your peripheral vision. Most people find their first test the hardest, and results usually improve with practice.

The first appointment also establishes a baseline. Glaucoma is monitored by looking at change over time, so these tests are repeated and compared.

How is glaucoma treated?

All current treatments work by lowering the pressure in the eye. This is the only approach proven to slow the disease. Pressure can be lowered with drops, with laser, or with surgery.

Dr O'Regan provides medical glaucoma care, SLT laser and YAG laser iridotomy personally. The small number of patients who need drainage surgery are referred to a glaucoma surgeon.

Next steps

Patients — contact the clinic to arrange an appointment.

GPs and optometrists — refer directly to Limerick or Ennis, including by Healthmail.