312.2 ¿Qué riesgos experimentan los niños y adolescentes en Internet?

The vast majority of the glaucoma research being done revolves around the use of drugs. This is to be expected, since drug companies are motivated by finan- cial considerations to fund research involving the development of new drugs. More governmental support of research would allow other approaches to be tested. Nevertheless, a number of studies over the years provide important clues as to the potential benefits to be derived from certain lifestyle factors.

Exercise

Aerobic exercise (the kind that makes your heart beat more rapidly) can be an important part of healthy living, reducing the risk of heart disease, cancer, and other degenerative ailments. Now, findings from one study point to a benefi- cial role that such exercise can play in the control of IOP. A small group of sedentary, middle-aged men and women with elevated IOP underwent a pro- gram of exercise conditioning using an exercise bike. After three months of such exercise, their average IOP fell by four and one-half points.1_{This is a very}

significant decrease, almost as much as one might expect from a typical glau- coma eyedrop. These people then stopped exercising and returned to their sedentary lifestyles. Three weeks later, their IOPs had returned to previous lev- els. A more recent study confirmed these findings. This demonstrates that exercise is an effective means of lowering IOP and can add to the effect of medication or even substitute for medication in mild cases.

I would caution that exercise such as running may cause a temporary rise in pressure in some people who have a less common form of glaucoma known

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as pigmentary glaucoma. The typical patient with this condition is a young, nearsighted male who develops an elevated IOP because of the structure or shape of his eye. Pigment becomes knocked off the back surface of the iris because of friction with the zonules. These dispersed granules of pigment can then clog up the drainage channels of the eye and damage them, resulting in a high IOP. Therefore, check with your physician before embarking on a vig- orous exercise program.

Smoking

People with glaucoma sometimes ask whether smoking has any effect on the disease process. Cigarette smoke contains nicotine, a stimulant that can affect blood flow. A recent study has shown, in fact, that blood flow to the eye is reduced in smokers. Further, long-term smoking is known to damage both small and large blood vessels. Therefore, if poor blood circulation to the optic nerve speeds up the optic nerve damage in people who have glaucoma, then smoking could have a negative effect. Studies in this area have yielded con- flicting results, however, so we can’t draw any definite conclusions. My own feeling is that we will eventually find that smoking increases the risk of glau- coma in one way or another. Since the final word is not yet in, should we advise people with glaucoma not to smoke? Absolutely. Everyone should be advised not to smoke. With a mile-long list of reasons not to smoke, we don’t really need another reason to recommend quitting.

Coffee

How about that common but questionably harmful addiction, caffeine con- sumption? Ever since the early part of the twentieth century, caffeine has been suspected of raising IOP. Some people have even recommended that it be used as a test for glaucoma, the idea being that a greater pressure rise would be seen in eyes susceptible to glaucoma than in normal eyes. The test did not prove to be of value. In one study, a large pressure rise was seen in only a small propor- tion of eyes in people known to have glaucoma.2_{Coffee drinking would be}

expected to provide even less caffeine than the amount used in these studies. In another study of glaucoma patients who drank either coffee or herbal tea, the pressure rise in the coffee drinkers was so slight as to be insignificant. In

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other words, it was not enough to cause any acceleration of optic nerve dam- age. It does not appear, then, that caffeine causes any significant change in IOP. What, then, should we advise glaucoma patients about drinking coffee? I would advise caution for two reasons. First, even if coffee drinking in the aver- age person does not cause much of a rise in IOP, it is possible that a few individ- uals might respond with a larger than average rise, and you never know whether you might be one of those individuals. This could indeed be harmful, because in the treatment of glaucoma, we always try to

keep the pressure under control twenty-four hours a day. Even a temporary rise in pressure could be harmful. Therefore, it might be use- ful for glaucoma patients who drink coffee to

have their IOP checked within an hour after drinking a cup or two. Only then will they know whether it makes any real difference in their own cases.

Second, whether coffee drinking affects IOP or not, we might also want to consider its effects on the optic nerve. At a given level of pressure control, does caffeine consumption in the form of coffee drinking increase the risk of pro- gressive optic nerve damage and visual field loss? The answer to this question is not known, but one study did evaluate the effect of caffeine on the circula- tion of the macula. As mentioned before, some glaucoma patients tend to have reduced circulation to certain areas around the optic nerve, including the mac- ula. This study found that consumption of the amount of caffeine in one cup of coffee caused an average 13 percent reduction in blood flow in the macula.3

This may have been due to blood vessel constriction induced by the caffeine. Since lessening the circulation around the optic nerve may worsen optic nerve damage in people with glaucoma, this study provides some cause for concern. Because of the uncertainty, my recommendation to glaucoma patients is to avoid caffeine-containing coffee.

Water

Any liquid consumed in quantity can raise IOP. It has been known for almost a hundred years that drinking a quart of water at one sitting can make IOP go up, especially in people who have a tendency toward elevated pressures to begin with. This finding became the basis for the water-loading test, which was supposed to help detect people with high pressures who were most at risk to

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Caffeine reduces circulation to the areas around the

develop glaucoma. (Recall that not everyone with high IOP has glaucoma.) People would drink a quart of water and then have their pressures checked every fifteen minutes for one to two hours. Unfortunately, the test did not prove to have good predictive value with regard to the likelihood of develop- ing glaucoma and has been abandoned. What we can learn from this is that glaucoma patients should refrain from drinking more than a pint of liquid at one time (unless they live in the desert and need to avoid dehydration!).

Alcohol

People who drink alcohol do not appear to be at increased risk for open angle glaucoma, and people with elevated IOP but no optic nerve damage are not at any increased risk to develop glaucoma-related optic nerve damage as com- pared with nondrinkers. In fact, alcohol can actually lower IOP. After drinking whiskey or even beer, the fall in IOP can be quite significant, especially in peo- ple with open angle glaucoma. Some people have speculated that alcohol might accomplish this by its effect on the pituitary gland, the “master gland” of the brain. However, alcohol was shown to lower IOP in a man whose pituitary gland had previously been surgically removed, so this cannot be the whole story. Alcohol most likely exerts its effect by virtue of what we call an osmotic effect. This means that the alcohol molecules cause a drawing out of water from the eye, resulting in a lowered pressure. The effect can last for two to three hours. Obviously, we cannot recommend heavy alcohol consumption as a way to keep IOP low, but it does suggest a way of rapidly lowering IOP at times that it is dangerously elevated, although other methods are also available. It also sug- gests that if you are about to undergo a pressure check on your eyes, you should refrain from alcohol consumption for the preceding three hours so that a reli- able and representative measurement of the IOP can be obtained.

Vitamin C

Another substance that can lower IOP by an osmotic effect is ascorbic acid, bet- ter known as vitamin C. Early reports indicated that megadoses of vitamin C, given either intravenously or by mouth, could cause large drops in IOP. Some of these studies used doses by mouth as large as 35 grams. (That’s about 400 times the current recommended dietary allowance!) Clearly, such a dose is

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impractical and likely to have pronounced side effects. More reasonable is the dosage of 500 milligrams four times a day used in a Swedish study of twenty- five patients with ocular hypertension (elevated IOP). An average drop in pressure of only a little over 1 millimeter of mercury was recorded. Such a minimal decrease is meaningless from a practical standpoint. Nevertheless, it is certainly possible that a few individuals might be unusually responsive to the effects of vitamin C and might benefit from treatment. The only way to know is to try it and have the IOP checked about two hours after a dose.

Vitamin B

The possible role of thiamin (vitamin B1) deficiency in glaucoma was investi-

gated in one study because low body levels of thiamin can cause optic nerve deterioration. A group of glaucoma patients was compared with a similar group of people who did not have glaucoma. Blood levels of thiamin were mea- sured, and dietary histories were taken. The study found no difference between the two groups in terms of the amount of thiamin they obtained from food, but the glaucoma patients did have lower blood levels of thiamin than the con- trols. It is hard to know what to make of this study, as it suggests that glaucoma patients may have some problem with their body chemistry or some absorp- tion problem that affects the amount of thiamin in their bodies. Unfortunately, no further studies were ever done to confirm these findings. Therefore, no rec- ommendations about thiamin supplementation can be made at this time.