Glaucoma is a group of eye conditions (typically classified as open- or closed-angle, and primary or secondary) characterized by progressive damage to the optic nerve head. Because the optic nerve transmits visual information from the eye to the brain, glaucoma can lead to vision problems if not treated early, and can eventually cause irreversible vision loss if left untreated.^[1]

Open-angle glaucoma is usually asymptomatic in the early stages, with visual symptoms developing subtly and gradually over time. The most common visual symptoms reported are needing more light, blurry vision, seeing glare, and difficulty seeing objects in peripheral vision.^[2]

Angle-closure glaucoma can present chronically, often without symptoms. However, it can also present acutely, with a sudden increase in the pressure inside the eye causing symptoms that include blurry vision, reddening of the eye, intense eye pain, severe headache, and nausea and vomiting.^[3]

A complete eye exam for glaucoma diagnosis typically includes five tests:^[4]

• Tonometry; to measure intraocular pressure
• Pachymetry; to measure the thickness of the cornea
• Ophthalmoscopy; to examine the optic nerve for damage
• Perimetry; to assess the field of vision
• Gonioscopy; to measure the eye’s anterior chamber angle

Elevated intraocular pressure (pressure inside the eye) is so far the only treatable risk factor for glaucoma. As such, current management strategies all aim to lower intraocular pressure. Depending on the situation, this is achieved with medications (applied topically to the eye or taken orally), laser treatment, surgery, or a combination of any of these.^[5]

Limited preliminary evidence suggests that a handful of supplements may have beneficial effects in glaucoma by reducing intraocular pressure, improving inner retinal function, increasing blood flow, or slowing visual field loss. These supplements include ginkgo biloba, blackcurrant anthocyanins, epigallocatechin-gallate, vitamin B3, and Erigeron breviscapus (a Chinese herb).^[6][7]

The available evidence examining the links between dietary patterns or dietary components and glaucoma risk is limited, mostly observational, and often conflicting. That said, the consumption of fruits and vegetables rich in vitamin A, carotenes, and nitrate has been linked to a reduced risk of glaucoma. Moreover, some studies have linked caffeinated tea intake with a lower risk of glaucoma. On the other hand, caffeine and caffeinated coffee transiently increase intraocular pressure (a risk factor for glaucoma onset and progression) in individuals with glaucoma, but do not seem to affect individuals without glaucoma.^[8]

A small number of studies have examined the potential efficacy of non-medical glaucoma treatments, including exercise, cannabis, acupuncture, and relaxation techniques.

The effects of exercise on intraocular pressure have been mixed, and seem to depend on the type and intensity of exercise. While marijuana use has been shown to effectively reduce intraocular pressure, its effects are short-lived, requiring dosing of 8–10 times per day for a sustained therapeutic effect. Clear evidence supporting the efficacy of acupuncture and relaxation techniques is lacking.^{[9][10][11][12]}

Although the exact causes of primary glaucoma have not yet been established, in most cases, the level of intraocular pressure is related to the degree of glaucomatous damage observed. Independently or in addition to intraocular pressure, other factors — including an insufficient supply of oxygen to the optic nerve head, excessive stimulation of the glutamate system, and the formation of free radicals and inflammatory cytokines — may individually or collectively contribute to the development of glaucomatous damage.^[13][14]