Glaucoma and intraocular pressure

What is the normal level of intraocular pressure?

Intraocular pressure is normally between 7 and 21 mm Hg (mm Hg = millimetres of Mercury).  The average value of intraocular pressure is 15 mm Hg. It tends to increase with age. We consider that an ocular pressure superior to 21 mm Hg is abnormal.

Is the ocular pressure always the same?

Ocular pressure is not stable and can vary depending on many factors. Ocular tension varies in the day. Usually, the pressure is higher in the morning and drops in the afternoon.  In patients with glaucoma, those variations are often greater. The pressure can be particularly high at times that are difficult to evaluate, like early in the morning around 6 a.m. Other factors affect the intraocular pressure as well. If we drink several coffees or sodas or if ones tie is very tight, the pressure will rise.  If, on the other hand, physical activity or alcohol use drop the eye pressure.

Does a raised tension mean there is glaucoma?

A raised ocular tension is not synonym to glaucoma. Some persons can have an ocular pressure higher than 20 mm Hg for more than 10 years and never have the disease.

There is a form of glaucoma that is not associated with excessive pressure. It is called “normal tension glaucoma”. Patients present all the signs of glaucoma except the rise in intraocular pressure. In those cases, it is necessary to drop the intraocular pressure to very low levels. In the absence of elevated intraocular pressure, diagnosis of glaucoma is made during the ophthalmological examination by analysing the back of the eye and the visual field.