Normal tension glaucoma: symptoms, tests and treatment

In most forms of glaucoma, fluid inside the eye (aqueous) cannot drain properly, pressure builds up and the optic nerve is damaged. In normal tension glaucoma the same kind of optic nerve damage occurs even though eye pressure measures within the usual range.

NICE Clinical Knowledge Summaries explain that it seems optic nerve fibres are more susceptible to damage in some people at pressures that are considered normal. Glaucoma UK uses several names for the condition: low tension glaucoma, normal pressure glaucoma and low pressure glaucoma.

The condition is not rare within the glaucoma family. NICE CKS describes it as occurring in a significant minority of people with primary open angle glaucoma. Because the pressure reading alone looks reassuring, it can be missed unless the optic nerve and visual fields are examined carefully.

Glaucoma UK says doctors do not fully understand why the nerve is damaged in NTG and that there may be several reasons. It may reflect reduced blood flow to the optic nerve; some people with NTG have other signs of altered blood flow such as cold hands or feet, migraine-like headaches or low blood pressure. It may reflect eye pressure that swings up and down more than is healthy, which can show up as small burst blood vessels near the optic nerve. Or the optic nerve may be structurally more easily damaged.

• Being older, since glaucoma is more common with age.

• Having a close blood relative with glaucoma.

• Having low blood pressure.

• Having problems with blood flow, such as cold hands or feet, migraines or Raynaud’s disease.

• Having an Asian background, according to Glaucoma UK.

As with other types of glaucoma, there are usually no symptoms early on. The NHS says glaucoma develops slowly over many years and is usually picked up during routine eye tests. Glaucoma UK explains that vision loss usually starts in the side vision, that central vision is clear for much longer, and that your other eye may fill in gaps so you do not notice.

One difference noted by Glaucoma UK is that NTG is more likely than other types of glaucoma to cause misty or blurry patches near the centre of vision. Where vision loss does occur it can lead to tripping over objects, difficulty with poor contrast, or finding it harder to see in the dark.

Glaucoma UK stresses that most people with glaucoma keep good vision for life, and that most people who lose significant vision were diagnosed late or had other eye or health conditions.

Diagnosis normally begins with a routine sight test at an optician, which can include measuring eye pressure, looking at the optic nerve and testing the visual field. If glaucoma is suspected you are referred to an ophthalmologist. The NHS says everyone should have an eye test at least every 2 years and that people at higher risk may need them more often.

In NTG the pressure is normal, so other findings carry more weight: changes to the optic disc and patches of visual field loss. Glaucoma UK lists further tests that may be used to examine the cornea thickness, view the drainage angle (gonioscopy, which is usually open in NTG) and photograph or scan the optic nerve.

Because other conditions can damage the optic nerve, some people have extra tests. Glaucoma UK mentions checking eye pressure several times in one day to see how much it varies, home blood pressure monitoring to see whether pressure dips, particularly with certain medicines, and an MRI scan to rule out other possible causes of optic nerve damage.

The NHS says there is no cure for glaucoma but treatment can slow the damage and help stop vision getting worse, with eye drops, laser treatment or surgery depending on the type and how vision is affected. Glaucoma UK explains that in NTG treatment aims to lower pressure even further, because this helps to stop or slow glaucoma.

Eye drops are a common treatment: some reduce the amount of fluid the eye makes and others help it to drain. Glaucoma UK says drops usually need to be used every day for life, that red, sore or itchy eyes are common side effects and that preservative-free drops or other options can be discussed.

Laser is sometimes used. Glaucoma UK says the most common laser treatment for NTG is selective laser trabeculoplasty (SLT), which aims a laser at the drainage channels; it says the effects typically last a few years and that SLT can usually be repeated when it wears off. Minimally invasive glaucoma surgery (MIGS) may be suggested if pressure stays too high after laser or drops, or if drops are a struggle. Glaucoma UK says most people with NTG will not need surgery, but a trabeculectomy or tube (shunt) operation is available if glaucoma is severe or getting worse.

Follow-up is central. The NHS says there will be appointments to monitor the eyes and check that treatment is working, and it stresses that it is important not to miss them. Glaucoma UK says follow-up can be at a hospital or in a community setting such as a high street optician or GP practice.

Telling close relatives is useful, since the condition can run in families. Glaucoma UK also points out that close relatives who live in the UK can have free eye tests from a certain age, and that everyone in Scotland can have free eye tests.

Coming to terms with a chronic condition that does not have a cure can be hard. Both the NHS and Glaucoma UK point to charity helplines and support groups, and the NHS signposts RNIB for people with sight loss.

Most people with NTG are looked after in an NHS hospital eye service, with community optometrists sometimes undertaking part of the monitoring. Sight tests are free for some groups on the NHS.

People who are seen privately usually have the same tests. Since NTG relies on comparing visual fields and optic nerve scans over time, keeping all reports together, and sharing them with whichever clinic is managing your care, makes follow-up more reliable.