Ocular Hypertension
Ocular hypertension means that the pressure in your eyes is higher than the normal range. Usually, it is detected by an optician or ophthalmologist but does not cause any symptoms. It is important that your eyes are checked regularly, just like going to your dentist, so that your optician can detect conditions like ocular hypertension.
The normal eye pressure is measure in millimetres of mercury and the range is between 11 and 21. If your pressure is higher than this, it would suggest you have ocular hypertension. This is not related to high blood pressure, however there are similarities in as much as high blood pressure usually does not cause symptoms, but it is also important to detect and treat as it can go on to cause other cardiovascular disease. According the to the Royal Automobile Club (RAC), tyre pressure should be checked every month. The eyes require significantly less attention, but a visit to the optician every one to two years is an important part of taking care of your own health.
If the pressure in the eye is elevated, there is a greater risk of developing glaucoma. There is around a 30% risk of developing glaucoma over 5 years with ocular hypertension. Treatment reduces this risk and the associated risk of visual loss significantly. Glaucoma is a condition where damage to the optic nerve and eventually to the field of vision occurs. It is important therefore when monitoring for ocular hypertension that the optic nerve is assessed (ideally with an OCT scan) and the visual field is assessed (ideally with a visual field test). Glaucoma is one of the leading causes of sight loss or blindness worldwide and as it is a lifelong condition, the incidence in the population is greater with age.
With a diagnosis of ocular hypertension, lifelong monitoring will be required and it may or may not require treatment at a particular stage. The decision to treat depends on having a high pressure but also on a number of other variables, such as corneal thickness. There is NICE guidance outlining who and when to treat, but in essence, the other variables are corneal thickness and age. If the thickness of the wall of the eye, the corneal thickness, is greater than average, then this is a protective feature. The pressure measured with greater than average corneal thickness may be an overestimate and the true pressure is actually lower. So it may be that in a patient with a thicker cornea, treatment can be deferred and only monitoring required, until the pressure is above a certain level. The opposite will be true for someone with a thin cornea.
Damage to the optic nerve is irreversible, so early detection and treatment is vital. There are now more and more treatment options and the first line include either selective laser trabeculoplasty (SLT) or eye drops. There are advantages and disadvantages to each and as with blood pressure medications, there is a stepwise manner in how they are utilised and the effect of the drops is additive. The treatment options depend on the patients preference, side effect profile, comorbitities and certain ocular features which may lead to a preference for one particular treatment.
One important consideration is the configuration of the drainage angle, and whether it is open or closed. An open angle with high pressure can be treated with SLT and eye drops as above. If the angle is narrow however, SLT cannot be used as this requires a laser to be applied to the trabecular meshwork in the angle, which increases the rate of outflow through the angle and therefore out of the eye. In cases of narrow angle, it may be that the narrow angle needs to be opened. This can be done with a YAG peripheral iridotomy (PI) or by removing the lens from the eye and replacing it with a clear, artificial lens, as in cataract surgery. The configuration of the angle can be assessed by a test called gonioscopy and this will be done in clinic by your doctor.
Due to the number of variables, it is best to understand a little about this condition before you attend your appointment so that you can make an informed decision about your personalised treatment plan at the end of the consultation.