Chapter 153
Flower-Power
The choriocapillaris, or choroid—that huge network of tiny blood vessels that supplies the retina—is probably the best-perfused part of the body. So it would be logical that high meat consumption would carry a significantly higher risk of macular degeneration. Those who consume more cholesterol have up to a 60 percent higher risk of developing early age-related macular degeneration, and saturated fats raise the risk to 80 percent. Drusen, the typical deposits at the back of the eye in macular degeneration, are cholesterol deposits with a composition similar to atherosclerotic plaques in the arteries. Their content of oxidized cholesterol is so high that it would be lethal for most cell systems. If you inject rats with LDL cholesterol for seven days, they develop “very similar” changes in the retina to those seen in the early stage of age-related macular degeneration in humans, but the current evidence that statin drugs can prevent or treat the disease in humans is not conclusive, so blood cholesterol may not actually play that large a role in macular degeneration.
Flower-Power
To maintain vision, two to three servings of green leafy vegetables are helpful, and berries as well. In see.nf/saffronvision I discuss how intervention studies show that berries improve vision in various respects, but with respect to macular degeneration, only one pigmented food has been studied: saffron. In the video I talk about all the relevant studies, and basically one can say that a small pinch of saffron (20 mg) a day can modestly but significantly improve visual acuity in older adults with mild or moderate age-related macular degeneration.
Diabetic retinopathy
Diabetes is another leading cause of blindness, as well as amputations and kidney failure. Fortunately, type 2 diabetes can be prevented or even reversed, as I describe in detail in the diabetes chapter in How Not to Die.
Glaucoma
Glaucoma, or “green cataract,” is now the most common cause of irreversible vision loss worldwide. In it, the optic nerve that connects the eye to the brain dies. Most often the cause is elevated intraocular pressure. Up to 40 percent of glaucoma patients go blind in at least one eye. To prevent this from happening, most treatments aim to lower intraocular pressure.
Holy kale
Is greenery the rescue here again? The nitric oxide that increases in the body when you eat dietary nitrate can equalize intraocular pressure, because it throttles the overproduction of aqueous humor (the fluid in the eyeball) and allows the excess to drain away. The pharmaceutical industry is already working on drugs similar to Viagra that can raise nitric oxide levels in the eye, but vegetables can already do that.
Only one in ten white Americans eats even a single serving of dark green leafy vegetables per month. The scientists who wanted to investigate the relationship between green leafy vegetables and glaucoma assembled a cohort of African American women who ate green leafy vegetables regularly (almost nine out of ten). The study participants who ate collards or kale more than once a month were only half as likely to have glaucoma as others who ate at most one serving. Apparently it doesn’t take much. With such small amounts per month, even studies with white participants could be interesting, so scientists in Boston took a look at the Harvard Nurses’ Health Study (97 percent white subjects) and the Harvard Health Professionals Follow-up Study (only one percent African American).
From decades of collected data on more than 100 000 men and women, there was indeed an association between high nitrate intake (especially from green leafy vegetables) and a significantly lower risk of glaucoma.
Not upside down
Is there anything else you can do? Aerobic exercise can lower intraocular pressure at least temporarily, and one study suggests that regular exercise may also keep it low long term. Bungee jumping, scuba diving, and inverted yoga poses (with the head down), however, do the opposite.
A study of almost 30 000 runners found that the amount matters, because longer distances and higher speed were associated with a lower incidence of glaucoma. Of course, with such observational data there is always the danger of reverse causation. Maybe exercise doesn’t preserve vision; rather, those who see well are more likely to exercise. And in fact, people with glaucoma tend to be less physically active than other people their age. A randomized controlled trial to test that is still lacking, but there are data on berry interventions.
Currants
Japanese scientists showed that the pigments of black currants slow glaucoma-related vision loss (details on this in see.nf/currants). This was accompanied by increased blood flow to the eye, but showed no change in intraocular pressure, suggesting that berries might also work for “normal-tension” glaucomas, in which the optic nerve dies despite normal intraocular pressure. In the United States, most “currants” are small raisins (vitis vinifera), because due to pressure from the timber industry, the cultivation of real currants (ribes nigrum) was banned until recently, since they can carry white pine blister rust, a tree disease.
Ginkgo?
As I explain in see.nf/gingkonic, one study cautiously found a positive effect of Ginkgo biloba extracts in open-angle glaucoma, and one of two additional studies found a significantly positive effect in angle-closure glaucoma. Anyone who wants to try it despite the unconvincing results should discuss it with their physician first, because the plant increases bleeding risk.
Nicotinamide
In the same video see.nf/gingkonic I report on a randomized, placebo-controlled, double-blind crossover study that showed that the B vitamin nicotinamide can reduce the risk of further visual field loss in glaucoma patients within a few months from 12 to 4 percent. In 2022, a study found a significant improvement in visual function, with the nicotinamide dose increased within two months from one gram to three grams per day; however, the results are not directly comparable, because pyruvate was also given here, another important factor in energy metabolism. I discuss the costs, confusing labeling, and possible side effects of nicotinamide elsewhere.
Cataracts
Age-related cataract, or “gray cataract,” in which the clear lens of the eye becomes cloudy, usually begins between 45 and 50 years of age. In low- to middle-income countries it is the leading cause of blindness, but in high-income countries it is responsible for only about 5 percent of blindness, since cataract surgery is available there as standard treatment. These days, high-tech cataract surgeries are a relatively quick, safe, and simple procedure with a rapid recovery. The clouded natural lens is removed and replaced with an artificial one, usually made of silicone or acrylic.
Overall, half of patients have visual acuity of only 20/40 after cataract surgery, but most commonly they complain of dysphotopsia, streaks or flashes of light caused by reflections inside the implanted lenses. Between 33 and 78 percent of cataract patients are affected by this, and as a rule it changes only with a new implant. The most serious complication is endophthalmitis, the entry of an infection into the eye. While this occurs only extremely rarely—at fewer than one in 2500 operations—it still affects so many that cataract surgeries are never performed on both eyes at the same time, so the patient does not go completely blind from infections.
Greenery again?
Can the clouding not be prevented? Cataracts are the direct result of oxidative stress, free-radical damage to the normally transparent crystallin proteins that make up the eye’s lenses. The oxidative stress comes from hyperbaric oxygen therapy, the sun’s natural UV radiation, artificial UV rays in tanning beds, or other high-energy radiation. Thus, in all 21 studies of health care workers who were exposed to X-ray radiation because they performed procedures such as angiograms, an increased cataract rate was found, and in 16 studies even a significantly increased cataract rate was found.