The pressure inside the eye, known as intraocular pressure (IOP), is a frequent topic of discussion during routine eye examinations. While elevated IOP is often associated with the sight-threatening condition of glaucoma, the relationship between high pressure and actual disease is complex. Ocular hypertension (OHT) and glaucoma both involve high internal pressure, but they are defined by a fundamental difference in their effect on vision, separating a risk factor from a diagnosed disease.
Defining the Key Difference
The key difference between Ocular Hypertension (OHT) and Glaucoma lies in the presence of optic nerve damage. OHT is defined as elevated Intraocular Pressure (IOP) above the normal range, without evidence of damage to the optic nerve or loss of visual field. It is considered a risk factor or precursor to disease.
Glaucoma, in contrast, is a progressive disease characterized by high IOP and measurable damage to the optic nerve. This damage results in permanent loss of vision, typically starting with peripheral vision. The optic nerve’s deterioration is the hallmark of glaucoma.
OHT is high eye pressure in an otherwise healthy eye, while Glaucoma is a pathological state where that pressure has initiated structural damage. Not everyone with OHT develops glaucoma, but the elevated pressure significantly increases the lifetime risk. Individuals with OHT are often referred to as “glaucoma suspects” and require close monitoring.
Measuring the Pressure
Intraocular Pressure (IOP) is measured using tonometry, a standard part of a comprehensive eye exam. This measurement is expressed in millimeters of mercury (mmHg). The normal range for IOP in the general population typically falls between 10 mmHg and 21 mmHg.
The most accurate method is Goldmann applanation tonometry, which involves gently touching the numbed eye surface with a pressure-sensing device. A common screening method is non-contact tonometry, often called the “air puff test,” which uses a brief burst of air to gauge internal resistance. Ocular hypertension is generally diagnosed when the IOP measures above 21 mmHg on two or more separate occasions.
Why Ocular Hypertension Matters
Ocular hypertension is the most significant risk factor for the development of open-angle glaucoma. The sustained force exerted by high IOP on the optic nerve can eventually compromise nerve function and lead to vision loss. Studies indicate that approximately 10% of people with untreated OHT may progress to glaucoma within five years.
The likelihood of progression is influenced by several factors used to assess an individual’s risk profile. A thinner central corneal thickness (CCT) is a strong predictor, suggesting greater susceptibility to pressure damage. Other factors that increase risk include increasing age, a family history of glaucoma, and specific ethnic backgrounds (African, Hispanic, or Asian). Higher baseline IOP measurements also carry a greater risk, especially pressures consistently above 30 mmHg.
Management and Monitoring
The clinical approach for Ocular Hypertension focuses on preventing progression to glaucoma through regular surveillance or preventative treatment. Active surveillance involves frequent check-ups (every 3 to 6 months) to monitor for the earliest signs of nerve damage. These check-ups include repeated tonometry, visual field tests for peripheral vision loss, and advanced imaging like Optical Coherence Tomography (OCT) to assess the optic nerve structure.
For individuals with high-risk features, such as very high IOP or a thin cornea, preventative treatment is initiated to lower the pressure before damage occurs. This typically involves pressure-lowering eye drops, such as prostaglandin analogs or beta-blockers, which reduce fluid production or increase its outflow. The goal in OHT management is to reduce the IOP to a “target pressure” that minimizes the chance of developing glaucoma.
For established glaucoma, treatment is initiated immediately and aggressively to halt progression and preserve remaining vision. While treatments for both conditions focus on lowering IOP, the urgency and intensity differ significantly because glaucoma involves irreversible damage. If eye drops are insufficient, laser procedures or conventional surgery may be used to improve the eye’s drainage system and achieve the necessary pressure reduction.