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Normal Pressure Glaucoma (NPG)

ROUTINE — Glaucoma

Symptoms

Presentation

  • Asymptomatic until advanced; often discovered during routine examination.
  • Gradual loss of paracentral and peripheral vision.
  • History of migraines, Raynaud phenomenon, or obstructive sleep apnea.
  • Vision loss continues despite intraocular pressures (IOP) within normal limits.

Clinical Findings

Diagnostic criteria

  • Glaucomatous neuropathy with IOP consistently ≤21 mm Hg.
  • Requires diurnal IOP documentation to ensure peaks are not missed.

Characteristic optic disc signs

  • Drance (splinter) hemorrhages: 2–4× more common than in high-tension glaucoma.
  • Focal notching of the neuroretinal rim (especially inferior/inferotemporal).
  • Acquired optic disc pits and peripapillary atrophy.

Visual field pattern

  • Dense paracentral defects closer to fixation than typical POAG.
  • Central vision threatened earlier in the disease course.

Systemic clues

  • Thin central corneal thickness (CCT).
  • Nocturnal systemic hypotension (often from over-treated high blood pressure).
  • Obstructive sleep apnea (nocturnal hypoxia).

Etiology

Pathogenesis

  • IOP-dependent damage: Damage occurs even at "normal" pressures.
  • IOP-independent damage: Vascular dysregulation, nocturnal hypotension, and vasospasm.
  • Accelerated retinal ganglion cell apoptosis.

Red Flags

  • Pallor out of proportion to cupping (rule out non-glaucomatous optic neuropathy).
  • Visual field defects respecting the vertical midline (suspect chiasmal compression).
  • Progression despite IOP in the low teens (target <10 mm Hg).
  • Splinter hemorrhages (sentinel sign of active progression).

Investigations

Clinical workup

  • Baseline glaucoma evaluation: IOP, gonioscopy, and automated perimetry.
  • Diurnal IOP curve: To rule out intermittent pressure spikes.
  • Color plate testing and VA: To screen for optic nerve pallor/compression.

Systemic & imaging

  • 24-hour ambulatory blood pressure monitoring: Check for "nocturnal dipping".
  • Sleep apnea screen (STOP-Bang) and polysomnography.
  • MRI brain/orbits with gadolinium: If neurological signs or atypical field loss present.

Treatment

Medical & laser

  • Target: Lower IOP by ≥30% (reduces progression risk from 35% to 12% per CNTGS).
  • Prostaglandin analogs (first-line) and SLT (effective primary option).
  • Brimonidine: Preferred over timolol due to potential neuroprotection (LoGTS trial).

Systemic adjustments

  • Coordinate with PCP to avoid evening/bedtime antihypertensive dosing.
  • Treat obstructive sleep apnea if identified.

Surgical

  • Trabeculectomy with MMC or tube shunt for very low IOP targets (often ≤10 mm Hg).

Clinical Pearl

A glaucomatous disc with "normal" IOPs still needs aggressive pressure lowering — and if the cup doesn't match the field (pallor > cupping, young patient), image the chiasm with an MRI before labeling it NTG.

Differential Diagnosis

  • • Primary open-angle glaucoma (POAG) with missed pressure peaks.
  • • Compressive optic neuropathy (tumor).
  • • Ischemic optic neuropathy (NAION).
  • • Intermittent angle-closure glaucoma.

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