What is meant by 'raised pressure'?

Broadly speaking, if a large population of people have their eye pressures measured, the mean average pressure will be about 16 mm Hg. Two standard deviations above that mean average will give an upper limit of ‘normal’ pressure of about 21 mm Hg. An eye is considered to have ocular hypertension if it is consistently above that level. This is obviously a mathematical calculation, but the risk of developing glaucoma rises appreciably with rising pressure and it has been shown that the risk of developing glaucoma is about ten times greater if a person has pressures between 21 and 29 than if the pressure is below 21 mm Hg. This is why everyone with ocular hypertension should be monitored carefully for the development of glaucoma and why some people have treatment to reduce the pressure to a more ‘normal’ level even when they don’t have glaucoma, i.e. in order to prevent the development of glaucoma. It is all a question of balancing the risk of the development of glaucoma against the risk of treatment.

Latest research suggests that ‘Normal Pressure’ in a Japanese population may be considerably lower than for other racial groups. People of Japanese origin should therefore be carefully examined in order to exclude the possibility of glaucoma. It is not yet know if a similar liability exists for other Asiatic peoples.