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Excerpt:

The Nighttime Blood Pressure Dip: A Hidden Driver in Normal-Tension GlaucomaNormal-tension glaucoma (NTG) is a type of glaucoma where the optic nerve deteriorates even though eye pressure is normal. In NTG, experts believe blood flow to the optic nerve plays a key role. The ocular perfusion pressure (OPP) – roughly the difference between blood pressure in the eye’s vessels and the eye’s internal pressure – drives that blood flow. If blood pressure falls too low, OPP drops and the optic nerve may starve for oxygen () (). Normally our blood pressure dips about 10–20% at night, which is healthy for the heart. But an excessive nocturnal dip (sometimes called “over-dipping”) can be harmful for the eye () (). In simple terms, a very large overnight BP drop can deprive the optic nerve of blood and speed vision loss.Ocular Perfusion Pressure: Why Low BP Can Hurt the EyeOPP is like the eye’s blood “fuel”. When systemic blood pressure (the “pump”) falls or eye pressure (“back pressure”) rises, OPP drops. Decades of research show that chronically low OPP is linked to glaucoma. For example, large epidemiology studies found that people with low diastolic pressure relative to eye pressure had much higher glaucoma risk (). In one study, subjects whose night-time diastolic OPP was under 55 mmHg had over 3 times the risk of glaucoma (). The Early Manifest Glaucoma Trial similarly showed that NTG patients who had low baseline blood pressure and perfusion lost vision faster (). The bottom line: if the ocular blood supply pressure is low (because of low systemic BP), the optic nerve is vulnerable.The Nighttime Blood Pressure DipAt night, the body naturally relaxes and lowers blood pressure (typically by 10–20%). In NTG patients, an exaggerated dip can create trouble. If the nighttime fall exceeds about 20%, physicians call this “over-dipping.” In one study of 54 NTG patients, half (27/54) were classified as over-dippers (). These patients had very large nocturnal falls in mean arterial pressure. Such drops can cause large swings in OPP, potentially triggering tiny ischemic episodes in the optic nerve (). Ophthalmologists now recognize extreme dips as a warning sign. A recent systematic review noted that “nocturnal hypotension and extreme nocturnal BP dipping are risk factors for the development and progression of open-angle glaucoma” (). In other words, letting the blood pressure plunge too low at night can directly damage the optic nerve. For example, one prospective NTG study found that patients whose nighttime blood pressure dropped about 10 mmHg below daytime levels had significantly faster visual field loss (). In NTG, each millimeter of mercury counts: a small extra drop at night can raise the chance of glaucoma progression substantially ().Evidence from 24-Hour Blood Pressure MonitoringTo clearly see the problem, researchers use 24-hour ambulatory blood pressure monitors. These devices record BP repeatedly through day and night. Ambulatory monitoring has confirmed the link between night-time BP dips and NTG progression. For instance, Charlson et al. (2014) prospectively monitored NTG patients and showed that those with nocturnal hypotension lost significantly more vision in one year (). They found that both the magnitude and duration of the night-time drop predicted who would worsen () (). In fact, Charlson’s team recommended that 24-hour BP monitoring “should become part

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