Normal Tension Glaucoma (NTG)

    What is Normal Tension Glaucoma (NTG)?

    NTG is a specific type of glaucoma where the optic nerve is damaged even though the pressure inside the eye stays within a “normal” range. Since the eye pressure isn’t high, this condition can be harder to spot than other types of glaucoma, usually requiring a more detailed and expert eye examination to detect.

    Characteristics of NTG

    • Optic Disc Changes: Patients exhibit typical glaucomatous cupping (thinning of the neuroretinal rim) and may frequently show “Drance hemorrhages” (small, splinter-shaped bleeds on the optic nerve head).
    • Visual Field Loss: The patterns of vision loss are similar to other types of glaucoma, but often tend to be deeper and closer to the central vision (macula), earlier in the disease.
    • Pressure Range: By definition, the measured IOP is consistently at or below 21 mmHg.

    Risk Factors

    • Ancestry: NTG is significantly more prevalent in Asian populations, particularly among those of Japanese and Korean descent.
    • Gender: It is more commonly diagnosed in women than in men.
    • Systemic Conditions: Sleep apnea, anemia, and cardiovascular disease are considered contributing factors.
    • Thin Corneas: Patients with naturally thin central corneal thickness (CCT) may have “under-read” IOP measurements, masking what might actually be higher pressure.

    Management

    • The “30% Rule”: The gold standard of treatment is to lower the existing pressure by about 30%—often aiming for a target around 10–12 mmHg—to give the nerve extra breathing room.
    • Beyond the Eye: Management often involves a “whole-body” approach, such as coordinating with a GP to ensure blood pressure doesn’t drop too low overnight.
    • Diagnostic Measurement: Frequent monitoring using OCT scans (to measure nerve thickness) and Visual Field tests is essential to ensure the disease isn’t quietly progressing.