Ocular hypertension may be defined as elevated intraocular pressure (IOP) in the presence of an anatomically and functionally normal anterior chamber angle, optic nerve head and visual fields. IOP is typically above 21mmHg on repeated measurements. A variety of studies have indicated that up to 5% of these patients will develop primary open angle glaucoma per year.
The Ocular Hypertension Treatment Study (OHTS) followed about 1500 patients utilising threshold automated perimetry and stereoscopic optic disc photography for 5 years, with subjects being randomised to topical medical treatment and no treatment groups. The results unequivocally showed that the treatment group was at a significantly reduced risk of developing glaucomatous changes to the optic disc and visual field loss. Risk factors for the development of glaucoma included the patient’s age, cup-to-disc ratio and their central corneal thickness (CCT). CCT can influence the measurement of IOP, with thinner corneas causing an underestimation of IOP and thicker corneas an overestimation of IOP. The OHTS concluded that ocular hypertension was the most important risk factor for developing primary open-angle glaucoma, and the institution of medical treatment could delay or prevent the development of glaucoma.
The condition is asymptomatic.
Persistently elevated IOP is the only sign. IOP is typically above 21mmHg on repeated measurements. Gonioscopy reveals a normal anterior chamber angle. The optic nerve head and retinal nerve fibre layer appear normal with the ophthalmoscope. Threshold automated perimetry reveals normal visual fields (VF). Pachymetry should be undertaken and often shows a greater than average CCT.
Common – about 10% of people over the age of 70
All forms of primary and secondary open angle glaucoma
Initially the management is one of review. Often a single IOP reading can be raised for a variety of reasons without glaucoma being present (see: Glaucoma – tonometry). For this reason, the normal procedure is often to arrange a subsequent visit to re-check the IOP and assess the CCT and VF.
Central corneal thickness should be measured, since a thick cornea (>580microns) will give an artifactually high intraocular pressure reading. Slightly raised IOP in the presence of a thick cornea and the absence of neuropathy or VF defect may be considered quite normal. Baseline optic nerve head imaging should be obtained, with photography or scanning laser ophthalmoscopy. Visual fields are assessed at threshold on at least an annual basis.
Patients may be followed or treated depending on the level of IOP, their age, CCT and family history of glaucoma. If IOP is below 24mmHg in the presence of normal optic discs, intact visual fields, and with average or above average CCT, the patient should be carefully reviewed every 6 months. When IOP is greater than 24mmHg, and where the fully informed patient elects to do so, medical therapy may be instituted.
Follow up should be as for primary open angle glaucoma (see: Glaucoma – primary open angle).
Ocular hypertensive patient with cup-disc ratio of 0.7 and no visual field loss. The cupping was bilateral and symmetrical and the intraocular pressures were 24mmHg. There were risk factors involving age, corneal thickness and family history. Increasingly, a risk management profile approach is being used to decide on treatment in ocular hypertension.
|Table 1A possible guideline to the management of ocular hypertension|
|Intraocular Pressure (IOP) mmHg||Range||Management|
|10 – 21||‘Normal’||Standard review cycle|
|21- 24||Borderline||Re-assess in a week or two|
|24-30||Ocular hypertensive||Review to check glaucoma-related risk factors and signs; consider medical therapy|
|30-40||Glaucomatous||Review to check glaucoma-related risk factors and signs; institute medical or surgical therapy|
|> 40||Acute glaucomatous||Urgent need to institute medical or surgical therapy|
* The listed management assumes:
- Absence of signs of angle closure, optic neuropathy, secondary glaucoma signs or visual field loss.
- Absence of other risk factors for developing primary open-angle glaucoma identified in the Ocular Hypertension Treatment Study (OHTS): reduced central corneal thickness (CCT), positive family ocular history, elevated vertical cup to disc ratio or advancing patient age. Other factors to consider may include life expectancy and cardiovascular status.