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Vasospasm, Cold Hands, and Normal-Tension Glaucoma: The Raynaud’s ConnectionGlaucoma is usually linked to high eye pressure, but in normal-tension glaucoma (NTG) the optic nerve is damaged even when eye pressure is normal. Researchers have long suspected that blood flow problems play a role in NTG. In fact, many NTG patients have symptoms of vascular dysregulation (abnormal control of blood vessels), such as Raynaud’s phenomenon, migraines, or low blood pressure () (). Raynaud’s phenomenon is a condition where cold or stress causes the small arteries in the fingers and toes to spasm and shut down blood flow (turning the skin white then blue) (). This exaggerated vasoconstriction is a clear example of vascular dysregulation. Interestingly, studies show that people with NTG are more likely to have cold hands (Raynaud’s) than those without glaucoma () (). In one study of 246 NTG patients and over 1,100 controls, symptoms like cold hands or feet were significantly more common in the NTG group (). Likewise, a review on NTG noted that “Raynaud’s phenomenon, migraine, [and] nocturnal systemic hypotension” are among the main associated factors for NTG (). These findings suggest that the optic nerve damage in NTG may come from inadequate blood supply rather than pressure. When blood vessels in the body (and eye) over-react to cold or stress, the optic nerve can suffer from repeated mild ischemia (low oxygen) and ‘reperfusion injury’ (damage when blood returns) () (). In short, NTG may in part be a vascular glaucoma, and Raynaud’s is one visible sign of that vascular trouble.How Cold Tests Reveal Vascular ProblemsTo study this connection, researchers use cold provocation tests and blood-flow measurements. A common test is the cold pressor test: a patient immerses a hand in ice water for about a minute, and doctors measure how much the finger temperature drops. In healthy people, the drop is modest; in someone with Raynaud’s or vasospasm it is large. For example, a 2021 study had 113 NTG patients (with well-controlled low eye pressure) dip a hand in ice water and then measured finger temperature () (). NTG patients showed a significantly larger temperature drop than normal controls (about 31.8% vs. 27.0% after one minute, P=0.042) (). Moreover, within the NTG group, those with greater finger cooling progressed faster: they lost visual field (vision) more rapidly than those with milder cooling (). In other words, “an excessive drop in finger temperature after ice water was significantly associated with faster visual field progression” in NTG (). This suggests that strong peripheral vasospasm predicts worse glaucoma, presumably because it reflects similar constriction in the eye’s blood vessels.Another study directly imaged the eye’s blood flow during a cold test (). Using laser flowmetry on the optic nerve head (ONH) and video capillaroscopy on fingernails, Takahashi et al. compared 14 NTG patients to 15 healthy controls (). They found that in NTG the optic nerve head vessels and finger capillaries showed abnormally large constrictions after cold stress, while facial vessels actually dilated (widened) more than normal (). In plain terms, NTG patients’ eye blood flow and finger blood flow drop much more in response to cold than in healthy people. This abnormal vasoreactivity (vessel response) is a hallmark of vascular dysregulation () (). Many older studies have likewise found nailfold capillary abnormalities in NTG and glaucoma patients (). For instance, combi