Normal Tension Glaucoma

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Definition

  • Variant of Primary Open-Angle Glaucoma (POAG) without elevated intraocular pressure
  • Characteristics: IOP <21mmHg, glaucomatous optic nerve damage, open angle, visual field defect corresponding to the optic nerve findings, no indications of secondary glaucoma or a non-glaucomatous cause of the neuropathy

Pathogenesis

  • Unknown
  • Associated with thin corneal thickness, abnormal vascular regulation (especially migraine, Raynaud’s phenomenon), systemic hypotension (including nocturnal blood pressure drops >20% (‘Dipper’)), particularly in cases of medication overuse, obstructive sleep apnoea syndrome, high levels of autoantibodies

Work-up

  • Patient history – inquire about associated pathologies
    • Migraine? Raynaud’s phenomenon? Cold hands/feet? Tinnitus? Low blood pressure? Obstructive sleep apnoea syndrome?
  • IOP normal
  • Optic disc: notching and splinter-shaped haemorrhages more common than in POAG
  • Visual field defects may be closer to fixation, steeper, and more localized than in POAG
  • OCT: Glaucoma-typical thinning of the RNFL, arcuate thinning of the ganglion cell layer
  • Assessment of vascular systemic risk factors
  • Ambulatory 24-hour blood pressure monitoring
  • Rule out non-glaucomatous optic neuropathies
    • MRI head
    • Consider blood tests such as vitamin B12, folic acid, complete blood count, ESR/CRP, treponemal serology, Lyme disease, serum ACE, plasminogen electrophoresis and autoantibodies

Sources

  • EyeWiki Normal Tension Glaucoma
  • The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease; Kalla Gervasio MD, Travis Peck MD et al; Lippincott Williams&Wilkins; 8th Edition (2021)
  • Kanski‚Äôs Clinical Ophthalmology: A Systematic Approach; John E Salmon MD; Elsevier; 9th Edition (2019)