Normal-tension glaucoma (NTG) is a condition where the optic nerve is damaged despite intraocular pressure (IOP) remaining in a normal range. Unlike other forms of glaucoma where high IOP is the cause, the optic nerve in NTG is vulnerable at lower pressures. This progressive damage to retinal nerve fibers can cause peripheral vision loss and eventually affect central vision if unmanaged.
Understanding the Rate of Progression
The progression speed of normal-tension glaucoma is highly individual, making a precise timeline difficult to predict. Some people experience very slow changes, while others see a more noticeable decline. Research from the Collaborative Normal-Tension Glaucoma Study (CNTGS) found that among untreated patients, visual field loss progressed at a mean rate of 0.41 decibels per year, with about 50% showing progression over a five to seven-year period.
The CNTGS also revealed the impact of treatment. When intraocular pressure was lowered by 30%, only 12% of patients showed progression over five years, compared to 35% in the untreated group. This demonstrates that medical intervention can substantially alter the disease’s trajectory.
However, not all individuals with NTG require immediate treatment. The study also found that 65% of eyes in the untreated group did not show any progression over a five-year period. This suggests that for a substantial number of patients, a careful monitoring approach may be a suitable initial strategy.
Key Factors That Influence Progression
Several factors beyond baseline eye pressure can influence the speed at which normal-tension glaucoma advances.
- Fluctuations in intraocular pressure (IOP), as large swings throughout the day can put stress on the optic nerve even if the average pressure is normal.
- The presence of optic nerve head hemorrhages, which are small bleeds on or near the optic nerve that are considered a marker of disease progression.
- Poor vascular health, as systemic conditions that affect blood flow can impact the optic nerve. Low systemic blood pressure, particularly at night, has been linked to faster progression.
- Genetic predisposition and family history, which can make the optic nerve more susceptible to damage at normal pressures. Research has also identified female gender as a risk factor in some populations.
How Doctors Track Progression
Ophthalmologists use a series of specialized tests to track the disease over time. These diagnostic tools allow them to detect subtle changes and determine the rate of progression. Identifying deterioration early informs treatment decisions to preserve vision.
Visual field testing, or perimetry, maps a person’s complete field of vision. This assessment identifies blind spots, known as scotomas. Repeated testing over time can show if these spots are enlarging or if new ones are developing.
Optical Coherence Tomography (OCT) provides a structural view of the eye. This non-invasive imaging creates high-resolution scans of the retina, measuring the thickness of the retinal nerve fiber layer (RNFL). Comparing scans from different visits allows a doctor to detect thinning, which is a direct sign of progression.
Doctors also use optic nerve photography to create a visual record of the nerve’s appearance. By comparing these images from one appointment to the next, an ophthalmologist can directly observe changes. This includes the nerve’s shape, color, and the extent of “cupping,” which is the excavation that occurs as nerve fibers are lost.
Medical Interventions to Slow Progression
The most effective strategy for slowing NTG progression is lowering the existing intraocular pressure (IOP). An ophthalmologist establishes a “target pressure,” an individualized IOP level intended to slow or halt damage.
Medicated eye drops are the first line of treatment. They work by decreasing fluid production in the eye or increasing its outflow to lower IOP. Consistent daily use is necessary for them to be effective.
Laser therapy is an option if drops are insufficient. Selective Laser Trabeculoplasty (SLT) uses low-energy laser pulses on the eye’s drainage system to improve fluid outflow. This procedure can lower IOP, reduce the need for drops, and can be repeated.
Surgical intervention may be recommended when other treatments are insufficient. Traditional surgery like a trabeculectomy creates a new drainage channel, while Minimally Invasive Glaucoma Surgery (MIGS) uses microscopic devices to enhance drainage. These approaches are reserved for advanced or rapidly progressing cases.