Ocular hypertension: raised eye pressure, monitoring and treatment

The front of the eye is filled with a clear fluid that is constantly made and constantly drained. The balance between the two sets the pressure inside the eye, which clinicians call intraocular pressure (IOP) and record in millimetres of mercury (mmHg). In ocular hypertension that pressure sits above the usual range on repeated visits, yet when the specialist examines the optic nerve and tests the visual field, nothing suggests damage.

That last point is what separates it from glaucoma. NICE Clinical Knowledge Summaries defines ocular hypertension as raised pressure with no signs of glaucoma, and glaucoma as a group of eye diseases that cause progressive damage to the optic nerve, often but not always with raised pressure. The NHS describes glaucoma as damage to the main nerve connecting the eye to the brain, which can cause vision loss if it is not diagnosed and treated early.

So a diagnosis of ocular hypertension is a statement about risk, not about disease. Most people with a raised reading will keep their sight, but the reading is the one thing doctors can measure and lower, so it is monitored and sometimes treated.

NICE CKS puts ocular hypertension at 3 to 5% of people over 40 in the UK, compared with about 2% for primary open-angle glaucoma, the commonest form of glaucoma. Because raised pressure is a known route into glaucoma, the same risk factors tend to be discussed for both.

The NHS glaucoma page lists the factors that raise the risk of glaucoma: being over 50, having a brother, sister or parent with it, being from a Black African, Caribbean or Asian background, and having other conditions such as short-sightedness, long-sightedness or diabetes. If you fall into one of those groups, the NHS notes you may be advised to have eye tests more often than the standard interval of at least every 2 years.

• Older age, especially from 50 onwards.

• A close relative with glaucoma.

• Black African, Caribbean or Asian family background.

• Short-sightedness, long-sightedness or diabetes.

A high number on a quick screening puff test is not enough on its own. NICE guideline NG81 says a decision to refer should not be based solely on pressure measured with non-contact tonometry, and suggests repeating the pressure or visual-field check on another occasion before referring unless the situation is urgent. The reading that carries weight comes from Goldmann-type applanation tonometry, where a small probe gently touches the numbed surface of the eye.

At the hospital eye clinic the guideline lists a full set of tests for diagnosing glaucoma and related conditions, which are also how ocular hypertension is distinguished from early glaucoma. They are set out in the table below.

Not everyone with ocular hypertension is treated. NICE guideline NG81 asks the clinician to assess the risk of future visual impairment at diagnosis, taking into account the level of pressure, corneal thickness, family history and life expectancy. It then recommends 360-degree selective laser trabeculoplasty (SLT) for people with newly diagnosed ocular hypertension whose pressure is 24 mmHg or more and who are at risk of visual impairment within their lifetime. People with pressure below 24 mmHg are advised to carry on with regular visits to their primary eye care professional.

SLT is a laser treatment applied to the drainage tissue of the eye. NICE tells clinicians to explain that it can delay the need for eye drops and can reduce, but not remove, the chance that drops will be needed at all, and that a second session may be needed later. If the effect of a successful first treatment wears off, a second SLT can be considered.

Generic prostaglandin analogue eye drops are offered when someone chooses not to have SLT, when SLT is not suitable (for example in pigment dispersion syndrome), while waiting for SLT, or when extra pressure lowering is still needed afterwards. If one drop is not tolerated or does not lower pressure enough, a drop from another class can be offered. These are specialist decisions and the right plan depends on your own measurements.

Ocular hypertension is a long-term watching brief. At each visit NICE advises tonometry and a slit-lamp check of the front of the eye, with visual-field tests and gonioscopy repeated when clinically indicated. The interval between visits depends on how the pressure is behaving and whether there is any sign that glaucoma is starting.

For people who are being treated, the guideline sets out the ranges in the table below. The clinician uses judgement to pick the actual date within each range.

• If glaucoma is diagnosed, the glaucoma pathway takes over.

• People who were referred but turn out not to need treatment can be discharged back to community eye care.

Ocular hypertension itself is quiet. The situation to know about is a sudden rise in pressure. The NHS lists intense eye pain, a red eye, tenderness around the eye, rainbow-coloured circles around bright lights, blurred vision, nausea and vomiting and a headache as symptoms of glaucoma that can develop suddenly. For this, the NHS advises calling 999 or going to A&E and says not to drive yourself.

Gradual changes are different. If you simply have concerns about your vision, the NHS advice is to see a GP or optician. Do not stop prescribed drops or miss clinic appointments because you feel well, since the aim of treatment is to prevent loss that you would not notice until it was advanced.

In the NHS pathway, an optometrist usually spots a raised reading during a sight test and refers on for the confirmatory tests above. NICE says monitoring of people with an established plan can be done by a suitably trained healthcare professional with knowledge of ocular hypertension, so follow-up can be shared between community optometry and the hospital eye service.

Seeing a private ophthalmologist generally means a faster appointment slot and the same battery of tests, but the clinical thresholds in NICE guidance still apply. Facilities and waiting times vary, so it is reasonable to ask which tests, such as visual fields and OCT imaging, are included and who will do the long-term review.