Glaucoma involves progressive damage to the eye’s optic nerve, which transmits visual information to the brain. This damage is often linked to internal fluid pressure that is too high for that specific eye to withstand. This measurable factor is called Intraocular Pressure (IOP), and managing it is the only proven method to slow or halt the disease’s progression. Since glaucoma often causes no symptoms until significant vision loss has occurred, regular monitoring of this pressure is important for preserving sight.
What Intraocular Pressure (IOP) Measures
Intraocular Pressure measures the force exerted by the aqueous humor. This fluid is constantly produced and drained to maintain the eye’s shape and nourish its internal structures. When the eye’s natural drainage system becomes obstructed or functions inefficiently, the fluid builds up, causing the IOP to rise.
This increased pressure presses on the fibers of the optic nerve, eventually leading to their death and resulting in vision loss. A statistical average for a healthy eye pressure falls within the range of 10 to 21 millimeters of mercury (mmHg). However, this general statistical range does not guarantee safety for someone already diagnosed with glaucoma, as an individual’s optic nerve may be more susceptible to damage at pressures well within that range.
Eye care professionals measure this pressure using a technique called tonometry, often utilizing the Goldmann Applanation Tonometer. Measurement involves gently touching the numbed eye surface with a probe or using a non-contact puff of air method. Since IOP can fluctuate throughout the day, a single reading represents only a snapshot of the pressure within the eye.
Determining Your Personalized Target Pressure
The question of a “good” pressure number for glaucoma has no single answer; the appropriate level is highly individualized. Instead of aiming for a general statistical number, ophthalmologists establish a personalized goal known as the Target Pressure. This target is defined as the maximum IOP level that is likely to prevent further optic nerve damage and subsequent vision loss over the patient’s lifetime.
The determination of this target is complex, relying on several factors. Severity of existing optic nerve damage is a key consideration, as advanced glaucoma generally requires a much lower pressure to stabilize the condition. The ophthalmologist also considers the patient’s baseline IOP—the pressure measured before any treatment began—to understand the pressure level that initially caused the damage.
For many patients, the target pressure is initially calculated as a percentage reduction from the baseline pressure. For example, a common starting point for newly diagnosed open-angle glaucoma is to aim for a 20 to 30% reduction from the untreated pressure. In cases of normal-tension glaucoma, where damage occurs despite initial pressures being in the average range, a reduction of 30% or more is often necessary to stabilize the disease.
For more severe disease, the pressure goal may be set at an absolute number, like 10 to 12 mmHg. Other factors, including the patient’s age, rate of disease progression, and the thickness of the cornea, also influence the pressure goal. This individualized approach ensures the pressure-lowering treatment is aggressive enough to protect the remaining vision.
Monitoring and Maintaining the Optimal IOP
Once the personalized target pressure has been set, treatment begins, typically utilizing prescription eye drops to enhance fluid drainage or reduce fluid production. When medications are insufficient, procedures like laser treatment or traditional surgery may be employed to improve the eye’s drainage pathway. The goal of any intervention is simply to consistently keep the IOP at or below the calculated target level.
The target pressure, however, is not a fixed goal and must be monitored and potentially adjusted throughout the patient’s life. The ophthalmologist uses structural and functional tests to confirm that the achieved pressure is protecting the optic nerve from further degradation. Structural assessments often involve Optical Coherence Tomography (OCT) scans, which provide detailed images of the optic nerve and the retinal nerve fiber layer to detect subtle thinning.
Functional tests, such as visual field tests, map the patient’s peripheral and central vision to determine if blind spots are expanding or worsening. If these monitoring tests show any evidence of disease progression, the current pressure is deemed insufficient, and the target must be lowered further. This means adjusting medications, adding new therapies, or pursuing more invasive procedures to achieve a lower, more protective IOP.