Glaucoma is a group of eye disorders that progressively damages the optic nerve, the bundle of nerve fibers responsible for transmitting visual information from the eye to the brain. This damage most often occurs because of excessively high pressure inside the eye, known as intraocular pressure (IOP). Since optic nerve damage cannot be reversed, the focus of glaucoma management is to prevent further vision loss by consistently lowering and controlling this pressure. The goal is to determine the specific, individualized pressure level that is safe for a patient’s eye, referred to as the target intraocular pressure.
Understanding Intraocular Pressure and Glaucoma
Intraocular pressure (IOP) is the fluid pressure inside the eye, maintained by a balance between the production and drainage of a clear fluid called aqueous humor. This fluid is produced by the ciliary body and normally drains out through the trabecular meshwork. In most forms of glaucoma, the disease impedes this drainage, leading to a fluid build-up and a subsequent rise in IOP.
The average IOP in people without glaucoma typically falls between 10 and 21 millimeters of mercury (mmHg). For many years, doctors used this general range as the goal for all patients. However, an IOP within the statistically average range can still be damaging to an optic nerve already compromised by glaucoma. A pressure considered “normal” for a healthy eye may be too high for an eye with the disease, meaning the target pressure for a glaucoma patient is almost always lower than the average range.
Establishing Your Personalized Target Pressure
There is no universal “good” eye pressure for a person with glaucoma. Instead, the ideal pressure is a highly personalized target pressure determined by the ophthalmologist. This target is the pressure level the doctor believes will prevent existing optic nerve damage from worsening. It is calculated using several factors, with the severity of the existing disease being the most influential component.
The extent of optic nerve damage at diagnosis dictates how aggressively the pressure must be lowered. A patient with mild glaucoma, where damage is minimal, may have an initial target pressure of 15 to 17 mmHg. Conversely, a patient presenting with severe or advanced damage requires a much lower target, often aiming for 10 to 12 mmHg or even lower to protect the remaining vision.
The initial IOP before treatment, known as the baseline pressure, is another factor in setting the goal. For many patients, the target pressure is set by aiming for a percentage reduction from this untreated baseline. A reduction of 20% to 30% from the initial pressure is a common starting point for newly diagnosed patients. For those with more advanced disease, a reduction of 40% or more may be necessary.
Additional individual characteristics also influence this personalized number, including the patient’s age and central corneal thickness. Younger patients generally require a lower target pressure because they have more years ahead for the disease to progress. A thinner-than-average cornea can lead to an artificially low pressure reading on the measurement device. This suggests the true IOP is higher than measured, which may prompt the doctor to aim for a lower target.
Treatment Options to Reach the Pressure Goal
Once the individualized target pressure is established, various treatments are available to reduce the eye’s pressure. The initial and most common intervention involves topical medications, specifically prescription eye drops. These medications work in two main ways: decreasing the eye’s production of aqueous humor or improving the fluid drainage through natural pathways.
If eye drops alone are insufficient to reach the target pressure, or if a patient cannot tolerate the side effects, laser procedures are often the next step. A common technique, Selective Laser Trabeculoplasty (SLT), uses a low-energy laser to treat the drainage angle, enhancing fluid flow out of the eye. This procedure can achieve a moderate pressure reduction, sometimes delaying or reducing the need for medications.
For more severe cases, or when drops and laser treatments have failed, surgical interventions become necessary. The conventional procedure is a trabeculectomy, which involves creating a new drainage channel to allow fluid to filter out of the eye into a small reservoir beneath the eyelid. Minimally Invasive Glaucoma Surgeries (MIGS) are also utilized, often involving the placement of microscopic stents or shunts to optimize fluid drainage.
Long-Term Monitoring and Adjustments
Achieving the target pressure is only the first part of managing glaucoma, as the process requires continuous, long-term monitoring. Regular check-ups with the ophthalmologist are essential to measure the IOP and ensure it remains consistently at or below the established target. Since pressure is not static and can fluctuate throughout the day, consistent control is important.
Beyond pressure checks, the doctor uses objective tests to monitor the optic nerve and visual function. These tests include optical coherence tomography (OCT) to scan the optic nerve and visual field tests to look for signs of vision loss. The ultimate measure of success is the stability of the optic nerve and the visual field over time, rather than just the pressure reading.
If glaucoma damage progresses despite the current pressure being at the target level, it means the initial goal was not low enough. In this situation, the target pressure must be revised and lowered further, often leading to an adjustment or intensification of the treatment regimen. Conversely, if the nerve and vision remain stable for many years, a less aggressive target may be considered, especially in elderly patients.