Ocular hypertension (OHT) is often confused with glaucoma because both involve elevated pressure inside the eye. While closely linked and sharing the same underlying cause, they are distinctly different states of eye health. OHT is a measurement finding that indicates risk, while glaucoma is an established disease causing irreversible damage. Understanding this distinction guides eye care professionals in determining appropriate monitoring and treatment plans.
Defining Ocular Hypertension
Ocular hypertension (OHT) is diagnosed when intraocular pressure (IOP)—the fluid pressure inside the eye—is consistently measured above the normal range. The normal range is generally considered to be between 10 and 21 millimeters of mercury (mmHg). OHT is present when a measurement exceeds 21 mmHg on two or more separate occasions, provided there is no associated damage to the optic nerve or visual field loss.
This pressure elevation results from an imbalance in the production and drainage of aqueous humor, the clear fluid that nourishes the front of the eye. This occurs if the eye produces too much fluid or if the drainage system, the trabecular meshwork, does not allow the fluid to exit efficiently. OHT is asymptomatic, causing no pain or changes in vision, and is only detectable during a comprehensive eye examination using a tonometer.
Defining Glaucoma
Glaucoma is a progressive disease defined by specific, measurable damage to the optic nerve, not merely by high pressure. This chronic optic neuropathy results in a permanent loss of peripheral vision, which often progresses unnoticed in its early stages. Sustained pressure can compress and damage the delicate fibers of the optic nerve, which transmits visual information from the retina to the brain.
Although high intraocular pressure is the most significant risk factor, glaucoma can occur even when pressure readings are within the normal range, a condition called normal-tension glaucoma. This confirms that glaucoma is fundamentally a disease of the optic nerve structure and function. Diagnosis requires evidence of characteristic nerve damage, assessed through visual field testing and specialized imaging of the optic nerve head.
The Key Distinction: Risk and Damage
The key distinction is that ocular hypertension is a risk factor, while glaucoma is the established disease. OHT indicates a high-pressure environment that makes the optic nerve vulnerable, but the nerve itself remains healthy. While not everyone with elevated pressure develops the disease, OHT significantly increases the likelihood of progression to glaucoma.
Doctors assess this risk using several factors beyond the pressure reading. These include a thinner central cornea, a family history of the disease, and the appearance of the optic nerve head. OHT is best understood as a precursor state that requires careful monitoring to prevent the onset of irreversible damage. For example, an untreated person with OHT has an estimated risk of developing glaucoma that can be as high as 10% over five years.
Treatment and Monitoring Protocols
Management protocols differ significantly for OHT compared to established glaucoma, reflecting the difference in severity. For patients with OHT and a low risk of converting to glaucoma, the initial approach is often watchful waiting. This involves regular monitoring of the intraocular pressure, optic nerve, and visual fields to catch early signs of damage.
If the risk of conversion is moderate to high, prophylactic treatment is initiated to lower the pressure and prevent the disease. This typically involves topical eye drops, such as prostaglandin analogs, which increase the outflow of aqueous humor. For diagnosed glaucoma, immediate and consistent treatment is mandatory to substantially lower IOP and halt the progression of existing nerve damage. Glaucoma treatment is a lifelong effort that may involve multiple medications, laser procedures, or filtration surgery like trabeculectomy.