Glaucoma

Glaucoma and raised eye pressure

Glaucoma is a word that, understandably, causes great concern as it is associated with sight loss. However, the truth is that many people and patients already being treated for glaucoma are very unlikely to lose their sight.

If you have visual field loss in a specific pattern, then you likely do have glaucoma. Thankfully even in advanced glaucoma most people keep good sharp central vision.  Peripheral vision is progressively lost, eventually leading to the inability to drive safely or legally. This loss of peripheral vision is not usually noticed and is usually only picked up by visual field testing.

What the words really mean

Here are some very important helpful facts to help you understand a little better.

GLAUCOMA means progressive damage to the optic nerve with associated visual field loss

The eye pressure in glaucoma can be low, normal or raised, which may sound surprising. Textbooks teach that normal pressure is less than 21mmHg, however, glaucoma can happen below that number or not happen if the pressure is higher than that number.

The most common type of glaucoma has no symptoms and may only be detected by an eye check. Long-sighted people over the age of 50 are more at risk of the less common acute glaucoma that causes very high pressure, pain and severe headaches. This is treated as an emergency and you would almost always know this was happening. For everyone else, there  are usually no symptoms until many years have passed when peripheral vision may be lost.  Eye tests every few years after the age of 45 can pick this up earlier.

Many people are told they are ‘at risk’ of glaucoma if their pressure is raised. This is true, but to quantify that risk at a single check is very difficult. It takes time, years usually, to know if glaucoma might progress and how quickly this will happen. The risk increases with each decade, meaning glaucoma is most common after the age of 70. Understanding glaucoma is best in hindsight when the rate of change is clear. We cannot predict accurately which patients might get worse later in life. Many progress very slowly and live a full life with no daily visual problems. A few patients – about 1 in 20 – progress quicker over three to five years. It is often the case that you do not have glaucoma but ocular hypertension.

Ocular Hypertension(OHT)  means raised pressure (over 21mmHg) but no damage to the nerve and full visual fields

If the pressure in your eye is over 21mmHg then you may be told you have raised pressure.  If it less than 30mmHg you may not be advised to have treatment, as long as everything else is healthy with your eyes and your general health. If you have a family history of definite glaucoma you may want to consider starting treatment.   

Only a small number of people with OHT develop glaucoma over the following five years

This means you can decide to have a regular check with examination and visual fields once a year or every two years. As long as your visual field is full and your nerves are unchanged in appearance then you should be fine.

A good question is ‘What is a normal pressure?’. The best answer is the pressure at which no damage occurs to the nerve. For some people this is as high as 30mmHg.

Key messages

• Early common glaucoma is usually unknown to the person and will not affect daily life

• A normal pressure is a level of pressure that is causing no damage

• More advanced glaucoma is often asymmetrical so with both eyes working together people can still drive and live normally even later in life.

• A small fraction of people with ‘open glaucoma’ are less fortunate, can develop advanced glaucoma in both eyes and can lose all vision. Usually this has taken many decades and occurs in late life. In about 5% of people, this can happen more quickly, over three to five years.

• Good general health and diet can reduce the risk of glaucoma damage.

• People with raised pressure have a variety of options to reduce the pressure and probably reduce the chance of damage to the optic nerve. These include drops, laser or surgery. There are different types of these three options, each with their own pros and cons. A plan of the most appropriate treatment should be discussed with each patient.

• There are special types of glaucoma that are rarer, often inherited and that have much higher pressure earlier and cause damage quicker. These include pigment dispersion, pseudo exfoliation, chronic narrow angle and other secondary causes.

• Always ask whether there is any evidence of progression when you have a check-up.

Regular eye checks after 45 years of age can help pick up early glaucoma or raised pressure. You may only need intermittent checks, but treatment may be advised.