Kazuhisa Sugiyama

Department of Ophthalmology Kanazawa University School of Medical Science,
Kanazawa, Japan

High prevalence of normal-tension glaucoma (NTG), 3.6% over 40 years in Japanese, reported in Tajimi Study. The prevalence of NTG in Japanese is higher than other countries and areas. The Tajimi Study also reported that intraocular pressure (IOP) distribution in NTG was similar to that in normal subjects. Our question is why the prevalence of NTG patients is so high in Japanese. Elevation of IOP over individual normal range should cause damage of axons at lamina cribrosa which stops axoplasmic flow. As a result, retinal ganglion cell death and retinal nerve fiber defect must occur and cause corresponding visual field loss. Individual normal range of IOP in NTG patients is probably lower than in high-tension primary open-angle glaucoma (POAG) or much lower than in ocular hypertension (OH). Lamina cribrosa in NTG might be more vulnerable to IOP than that in OH or POAG. Deformation of weak lamina cribrosa by normal pressure leads to axonal damage and retinal nerve fiber defect. Connective tissue of lamina cribrosa in NTG could be weaker than that in OH or POAG. The cause of high prevalence in NTG might be attributed to the high prevalence of weak lamina cribrosa in Japanese.

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