What is ocular hypertension?
Ocular hypertension simply means a raised pressure within the eye. It is not glaucoma, although in many cases people with glaucoma also have a raised pressure within their eyes and it does mean that someone with ocular hypertension is at increased risk of developing glaucoma, which is why it is most important for people with ocular hypertension to be monitored carefully in order that any glaucoma that does develop is detected at the earliest possible stage when treatment is most effective.
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 ethnic 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.
What creates pressure within the eye?
Eye pressure (intraocular pressure) is controlled by a watery fluid called aqueous humour, which fills the front part of the eye. This fluid is made in the ciliary body (a ring of tissue behind the coloured part of the eye, which is called the iris).
It flows through the pupil and drains away through tiny drainage channels called the trabecular meshwork. This is situated in the drainage angle between the cornea (the clear window at the front of the eye) and the iris.
In a 'normal' eye there is a balance between the production and the drainage of this fluid, but in some eyes, there is an imbalance.
Most cases of ocular hypertension occur because the flow of fluid out of the eye becomes restricted and the pressure in the eye rises.
Are some people at increased risk of developing ocular hypertension?
Yes, there are several risk factors which make the development of ocular hypertension more likely and they tend to be cumulative in their effect.
Age: Ocular hypertension becomes much more common with increasing age so regular testing from about the age of 40 is recommended.
Race: People of African-Caribbean origin are more likely to develop ocular hypertension than people of a European origin. The condition also tends to develop at an earlier age so regular testing from about the age of 30 is advisable.
Family History: It is unlikely that a person will be aware of a history of ocular hypertension within the family, but any history of glaucoma in a close blood relative leads to an increased risk of developing glaucoma.
Diabetes: People with diabetes may be at increased risk of developing glaucoma, although it is not known if there is a direct link between the two conditions.
Diagnosis: 3 tests
What should I do if I fall into one or more of these risk categories?
As has already been discussed, ocular hypertension is a major risk factor for the development of glaucoma. If ocular hypertension has already been diagnosed, then it should be expected that regular routine eye examinations will be needed in order to make sure that the condition has not developed into glaucoma. These routine examinations may be carried out at the hospital or they may be carried out by an optometrist depending on the level of pressure and whether or not treatment has been prescribed.
However, anyone who is in one or more of the risk categories mentioned in the who is at risk section, should have an eye examination every year or two, whether it be at the hospital or at an optometric practice (opticians) which includes all three glaucoma tests so that if glaucoma has developed, it is detected at the earliest possible stage.
The three tests are:
Ophthalmoscopy: An examination of the optic disc with a special torch or a slit lamp.
Tonometry: A measurement of the pressure within the eye (the intraocular pressure).
Perimetry: A check of the visual field to see if there are any signs of sight loss in the off centre part of the vision which could be a sign of the development of glaucoma.
How is ocular hypertension treated?
As has already been mentioned, it is not appropriate to treat all cases of ocular hypertension, but if the risk of the development of glaucoma is considered to be significant, the ophthalmologist may decide that the balance of risks and benefits is such that treatment is appropriate.
If this is the case, the most usual type of treatment to be prescribed is eye drops that control the pressure within the eye (these are the same drugs that are used to control glaucoma) by either reducing the amount of aqueous being produced by the eye (the ciliary body) or increasing the rate of drainage.
There have been major advances in these forms of treatments in recent years and eye drops are now more effective and have fewer side effects than those that were previously available.
What if my ocular hypertension cannot be fully controlled?
Ocular hypertension itself does not damage the vision, but if it develops into glaucoma then there is a very small risk to sight.
More than 90% of people diagnosed with glaucoma today will retain useful sight for life and if you have been diagnosed with ocular hypertension and have received the appropriate level of monitoring then any glaucoma will have been detected at a very early stage when little damage to the field of vision will have occurred.
At the point at which ocular hypertension has developed into glaucoma, the consideration of risk and benefit of treatment changes, and there are a number of treatment options available which would not normally be suggested for a person with ocular hypertension unless the level of the intraocular pressure were very high.
It would therefore still be reasonable to expect to retain useful sight for life, although the treatment and monitoring regime will inevitably change.
Can I continue to drive with ocular hypertension?
Ocular hypertension is not glaucoma and there is no requirement to inform the Driver and Vehicle Licensing Agency (DVLA) about the condition, unless it develops into glaucoma in both eyes (in which case you are required by law to inform the DVLA).
Nevertheless, it is important that your general eyesight is good enough to allow you to drive so if you have any doubts it is best to ask your optometrist or ophthalmologist.
What if my ocular hypertension cannot be fully controlled?
Ocular hypertension itself does not damage the vision, but if it develops into glaucoma then there is a very small risk to sight. More than 90% of people diagnosed with glaucoma today will retain useful sight for life and if you have been diagnosed with ocular hypertension and have received the appropriate level of monitoring then any glaucoma will have been detected at a very early stage when little damage to the field of vision will have occurred.
At the point at which ocular hypertension has developed into glaucoma, the consideration of risk and benefit of treatment changes and there are a number of treatment options available which would not normally be suggested for a person with ocular hypertension unless the level of the intraocular pressure were very high. It would therefore still be reasonable to expect to retain useful sight for life, although the treatment and monitoring regime will inevitably change.