Glaucoma is an eye disease in which the optic nerve is damaged, often by high pressure inside the eye. Standard treatment focuses on lowering intraocular pressure (IOP). However, doctors increasingly recognize that poor blood flow and other factors also contribute to nerve damage. One molecule under study is endothelin-1 (ET-1). ET-1 is a natural peptide (small protein) made by blood vessel cells and eye tissues that is the most potent vasoconstrictor in the body (). In other words, it strongly narrows blood vessels. When ET-1 levels are high, retinal and optic nerve blood vessels can tighten, reducing oxygen and nutrients to the optic nerve. In this way, too much ET-1 may “stress” the optic nerve fibers and contribute to glaucoma damage (). In fact, many studies find ET-1 is elevated in glaucoma patients’ blood and eye fluid () (). Here we explain what ET-1 does in the eye, summarize the evidence linking ET-1 to glaucoma damage, and discuss possible treatments that block its pathway (rather than using ET-1 itself as a drug).

What is Endothelin-1 and How Does It Affect the Eye?

Endothelin-1 (ET-1) is made by cells lining blood vessels throughout the body, and it helps regulate normal blood pressure and flow. In the eye, ET-1 is produced in several places: the retina, the blood vessels of the eye, the retinal pigment epithelium, the optic nerve head, and the structures that make and drain fluid (aqueous humor) (). Under normal conditions, ET-1 keeps a balance: it tightens vessels when needed and releases them when other signals come in.

However, ET-1 is a very powerful constrictor. Rosenthal and Fromm describe ET-1 as “the most potent vasoactive peptide known to date” (), meaning none of the body’s chemicals narrows vessels more strongly. In the eye’s tiny blood vessels, overactive ET-1 can seriously reduce blood flow. For example, if ET-1 rises, it causes vasoconstriction (narrowing) of blood vessels in the retina and optic nerve head (). This can trigger ischemia (low blood supply) in the optic nerve. Over time, that lack of oxygen and nutrients can injure or kill the retinal ganglion cells (the nerve cells in the retina whose fibers form the optic nerve). Rosenthal et al. note that such ischemia “is assumed to contribute to the degeneration of retinal ganglion cells” in glaucoma ().

ET-1 also affects fluid drainage in the eye. Aqueous humor (the fluid in the eye) normally drains out through a spongy tissue called the trabecular meshwork. ET-1 makes those meshwork cells contract (), which can reduce outflow and potentially raise eye pressure. Indeed, Rosenthal’s review suggests that inhibiting ET-1 can lower IOP and protect nerves (), although not all studies agree on ET-1’s pressure effects. In summary, too much ET-1 can both increase eye pressure slightly and pinch the eye’s blood supply, creating a “double hit” to the optic nerve.

Evidence Linking ET-1 to Glaucoma Damage

Many clinical studies find that ET-1 levels are higher in glaucoma. For example, a recent meta-analysis pooled data from over 1,000 glaucoma patients and healthy people. It found that plasma ET-1 was significantly higher in patients with primary open-angle, normal-tension, and angl

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