Normal Tension Glaucoma: Are We Missing It?
Prevention is better than cure – especially when there is no cure
Tony Realini |
At a Glance
- Clinicians frequently fail to detect normal tension glaucoma (NTG) – until it reaches an advanced stage
- The reason? Failing to suspect NTG in patients whose IOP is within the normal range
- Given time and resource constraints, the clinician might not perform a careful optic nerve exam, thereby missing the early signs of glaucomatous optic neuropathy
- This article reviews how to identify those who need treatment – and when and how to treat them
In clinical practice, we frequently encounter patients who present with almost all of the diagnostic findings of primary open-angle glaucoma (POAG) – but whose intraocular pressure (IOP) is in the normal range. It is a challenging clinical scenario because, for decades, we believed elevated IOP was the defining diagnostic feature of glaucoma. Today, it’s recognized that elevated IOP is not integral to a diagnosis of glaucoma when optic nerve damage is observed in the absence of other explanations for disc abnormality and/or visual field loss (1). Yet, the myth that elevated IOP must be present for a diagnosis of glaucoma persists, which means that many clinicians frequently fail to detect normal tension glaucoma (NTG) until it reaches an advanced stage. If a clinician fails to suspect NTG in patients whose IOP lies within the normal range (12–22 mmHg), they may decide not to perform a careful optic nerve exam, and thereby miss the early signs of glaucomatous optic neuropathy (2).
Without high IOP, NTG is harder to detect and more challenging to manage than high tension POAG (HT-POAG) in several important ways. In a large epidemiologic study assessing the prevalence of glaucoma, it was found that an estimated 30 percent of patients diagnosed with OAG had NTG (3)(4), and Asian populations appear to be particularly prone to NTG; the Japanese Tajimi study cited a POAG prevalence of 3.9 percent, of which 92 percent had NTG (3)(5). In this article, I will examine the differences between NTG and HT-POAG and outline strategies for optimal detection and management.
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