COMMENTARY

(S)pot Check on Alternative Treatments for Glaucoma

Shuchi B. Patel, MD

Disclosures

September 17, 2018

Glaucoma is an ocular condition afflicting almost 3 million people in the United States.[1] It is the number one cause of irreversible blindness worldwide.[2]

Glaucoma causes vision loss by damaging the optic nerve. This leads to loss of peripheral vision and eventually blindness. The damage to the optic nerve is multifactorial, but increased ocular pressure is the most modifiable variable. Therefore, first-line treatments for glaucoma include topical eye drops aimed at lowering intraocular pressure (IOP). If topical treatments fail or are insufficient, laser and surgical treatments are aimed at lowering IOP. Given the possible side effects and costs of therapy, some patients investigate the use of adjunctive therapy for treatment of glaucoma.

The most widely discussed possible alternative treatments that have been proposed include marijuana, gingko biloba, and bilberry.[3] Some of them aim to lower the eye pressure, similar to current conventional therapies; others are aimed at increasing ocular blood flow to protect the optic nerve from damage that may be occurring from other factors. The effects of these three treatments are the most studied among alternative treatments for glaucoma, although other herbs and lifestyle modifications also undoubtedly have been suggested.

Marijuana

As of now, eight states have broadly legalized marijuana, including recreational use, and over 20 more states have legalized medical marijuana.[4] Thus, much attention has been given to the idea of marijuana use for the treatment of glaucoma.

The idea that marijuana can be helpful in treating glaucoma dates to the 1970s. Previous and recent studies have shown that smoking marijuana lowers the IOP of people with glaucoma.[5,6,7] Further studies have shown that active ingredient in lowering IOP is a compound known as tetrahydrocannabinol (THC). The concentration of THC in marijuana has increased from about 2%-3% in the 1970s to about 20% currently.[8] Thus, the IOP-lowering effect of marijuana is present when smoked or when a form of its active ingredient is taken as a pill or by injection.

Yet, the stance of the American Glaucoma Society[9] as well as the American Academy of Ophthalmology[10] is that marijuana is not an approved therapy for glaucoma in any form. The major reason for this is that even though marijuana does lower IOP, the duration of the effect is about 3 or 4 hours. Glaucoma needs to be treated 24 hours a day; therefore, patients would have to use marijuana six to eight times a day around the clock to receive the benefit of a consistently lowered IOP. This short duration of effect is a major drawback for the use of marijuana as a glaucoma treatment.

Also, owing to marijuana's mood-altering effect, using marijuana that much would leave patients unable to function normally and affect such abilities as driving.

Thus, the use of marijuana, whether smoked or ingested, is not advocated or supported by the American Glaucoma Society[9] or American Academy of Ophthalmology.[10]

Gingko Biloba

Ginkgo biloba has been used in Chinese traditional medicine for centuries. It has been used for such conditions as memory loss, concentration difficulties, confusion, depression, anxiety, dizziness, tinnitus, and headache.[11] In addition, ginkgo has been shown to have neuroprotective effects and antioxidative properties and to increase blood flow through vasodilation and reducing blood viscosity.[12]

Few studies looking at the effect of gingko on ocular vasculature have been published, but some support that it may improve ocular blood flow.[13,14] Another study showed a reduction in ganglion cell loss in rats receiving oral gingko extract.[15]

Although blood flow may be improved and cell death decreased, studies have not been able to reproducibly show any functional improvement. Visual field outcomes in patients consuming gingko have had variable results; some studies found slowed progression of visual field damage,[16] whereas other studies showed no statistically significant improvement in measured parameters of field damage.[17,18]

The side effect profile of gingko when dosed at 80-600 mg daily is very low, with no significant side effects reported in systematic reviews of the literature.[11] Therefore, the use of gingko is popular and may provide some benefit to patients with glaucoma, especially those with normal-tension glaucoma, but it cannot be advocated to replace conventional treatment.

Bilberry

Bilberry is the extract of European blueberry and is available in nutritional and health stores. Its health benefit is advertised as an antioxidant.[19]

In terms of eye health, advocates claim it can protect and strengthen the capillary walls of the eyes, therefore making it protective against glaucoma, cataracts, and macular degeneration.[16] Currently, there is no evidence that it is effective in the treatment or prevention of glaucoma,[20] although it has been shown to prevent retinal ganglion cell death in animal models.[21] Further studies to correlate this to actual suppression of glaucomatous cell death as well as preservation of visual function have to be performed before there is evidence to support its use.

Side effects of bilberry are mostly due to an allergic reaction, but otherwise it is thought to be relatively safe.

No Replacement for Conventional Therapy

There is no alternative treatment with a proven benefit in the treatment of glaucoma that can be used on a regular basis or to replace conventional therapy.

Marijuana does lower IOP, but the duration of action is short and therefore not sustainable to maintain 24-hour IOP control. Herbal remedies, such as gingko and bilberry, may have some neuroprotective properties, but further studies need to be conducted to confirm visual benefits. Other herbs, diet modification, acupuncture, and exercise have also been suggested, but there is not enough evidence to support or discourage such changes.

Conventional treatment cannot be discarded, but alternative options may emerge as further studies of complementary therapies evolve.

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