Ординатура / Офтальмология / Английские материалы / The Eye Care Sourcebook_Lavine_2001

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other words, it was not enough to cause any acceleration of optic nerve damage. 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 average person does not cause much of a rise in IOP, it is possible that a few individuals 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 useful 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 progressive 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 circulation of the macula. As mentioned before, some glaucoma patients tend to have reduced circulation to certain areas around the optic nerve, including the macula. 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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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 developing 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 compared 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 people 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 suggests 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 reliable and representative measurement of the IOP can be obtained.

Vitamin C

Another substance that can lower IOP by an osmotic effect is ascorbic acid, better 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 twentyfive 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 B1

The possible role of thiamin (vitamin B1) deficiency in glaucoma was investigated 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 measured, 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 controls. 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 absorption problem that affects the amount of thiamin in their bodies. Unfortunately, no further studies were ever done to confirm these findings. Therefore, no recommendations about thiamin supplementation can be made at this time.

Rutin and Pilocarpine

In the late 1940s, Dr. Frederick Stocker of Duke University began looking for new and unusual approaches to treating glaucoma. He performed studies on what we call the blood-aqueous barrier in the eye. The blood-aqueous barrier refers to the finding that as blood travels through the part of the eye called the ciliary body, a filtration process occurs. A watery fluid (aqueous humor) is secreted into the eye, but because of the blood-aqueous barrier, many substances from the blood are kept out of the eye. Inflammation and certain chemicals or drugs can cause a breakdown of this blood-aqueous barrier, however. When that happens, protein and other substances from the blood enter the eye, and sometimes the ability of the fluid to drain out of the eye

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becomes compromised, resulting in a rise of the IOP. Dr. Stocker knew that pilocarpine, one of the medicines used to treat glaucoma, can break down the blood-aqueous barrier somewhat, and he was concerned that this might interfere with the pressure-lowering effect of pilocarpine in some of his patients.

He looked at ways of restoring a broken-down blood-aqueous barrier to its normal state. One group of substances he studied was the flavonoid group. Flavonoids are a diverse group of chemicals pre-

sent in foods, and many of them have antioxidant, anti-inflammatory, and other properties. Unlike vitamins, there is no recognized minimum requirement in the diet for flavonoids, although in the past they have sometimes been

referred to as vitamin P. At one time, physicians could prescribe flavonoid preparations. The FDA (Food and Drug Administration) decided that there was no proof that flavonoids were beneficial, so it put an end to that. Not to worry— you can still get them as a supplement over the counter.

Dr. Stocker did some studies on a flavonoid called rutin and found evidence that it could restore the blood-aqueous barrier broken down by medications. He also found other flavonoids to be promising. The next step was to use rutin in a group of glaucoma patients being treated with pilocarpine. He first used 20 milligrams three times a day and, in other studies, increased the dosage to 50 milligrams three times a day. He found a pressure-lowering effect that he attributed to the rutin, and he felt the effect was most marked in patients in whom pilocarpine had produced the least lowering of pressure. Further studies were promised but apparently never done.

My own clinical experience with rutin in pilocarpine users has been limited and inconclusive. If there is a beneficial effect, it might also be seen with other drugs in pilocarpine’s class, such as carbachol and echothiophate iodide (Phospholine Iodide). Since the use of a rutin supplement seems harmless enough, it would certainly be worth a try.

Meals and Diurnal Rhythm

The timing of meals may actually play an important role in the fluctuations of IOP during the day. Over eighty-five years ago, Dr. Carlo Pissarello, an Italian physician, performed studies on the different factors that might affect the IOP

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over the course of a day. It has long been known that people have what is called a diurnal rhythm to their IOP, which means that the IOP may be higher or lower at certain times of the day. Experience has shown that IOP is often highest right after awakening in the morning. Dr.

Pissarello studied this rhythm in patients with different types of glaucoma.4

He made a very interesting observation. The IOP tended to be higher before meals but

lower right after meals. This could certainly help explain why the IOP in many people is highest early in the morning before breakfast, as the overnight period generally represents the longest period of abstention from food over a twenty- four-hour period. This finding also suggests some intriguing possibilities. For example, could a “grazing” type of diet, in which one eats perhaps six small meals a day rather than three large ones, help keep the IOP under better control? Grazing diets may actually be a more natural type of diet, and they have already been found to be beneficial in weight loss and cholesterol-lowering programs.

The concept of the timing of meals and its relation to IOP has not been adequately studied, and there have been conflicting opinions. Sir Stewart Duke-Elder, a renowned English ophthalmologist, stated that he did not feel that the daily rhythm of IOP was related to the intake of food, but he did not cite any studies to bolster his position. Dr. H.-J. Merté, the director of a university eye clinic in Germany, reported that the intake of food could indeed cause a change in the IOP rhythm in eyes without glaucoma, but he did not find a consistent pattern in the eyes of people with glaucoma.

In my own experience, I have had the distinct clinical impression that the timing of meals does influence the IOP. I have often measured patients whom I’ve suspected of having swings of IOP both before and after lunch, and occasionally early in the morning before breakfast. I want to be sure that their pressures are under good control at all times. Whether you have glaucoma or just ocular hypertension, you might want to have your pressure checked before breakfast while you are “at your worst.”

The Rice Diet

Now that we’ve discussed the timing of meals, how about food choices? Do specific foods have any effect on IOP? Again we must turn to an interesting

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study performed by Dr. Stocker and his colleagues. At that time, Dr. Walter Kempner, an internal medicine specialist at Duke University, had devised a diet called the “rice diet” for his patients with hard-to-control high blood pressure. The diet was limited to rice (brown or white), sugar, fruit, and fruit juices, and it was supplemented with vitamins and iron. This diet provided much less protein than the recommended dietary allowance. Only 2.5 percent of calories came from fat, and there was minimal sodium and chloride (salt). An impressive lowering of blood pressure was achieved, and, as an added bonus, blood cholesterol levels dropped by an average of 25 percent.

Dr. Stocker decided to see what effect this diet would have on the IOP in a group of people without glaucoma. He reported that right after beginning the rice diet, these people showed a striking reduction in IOP. He

commonly observed long-lasting reductions in pressure in the range of 5 to 7 millimeters of mercury.5 He was hard pressed to explain the phenomenon, but he guessed that the ultralow salt content (0.2 grams of sodium a day) of the diet might have been the factor responsible for lowering the IOP. Further studies on glaucoma patients were never performed.

There may be a better explanation for the apparent effect of the rice diet on IOP, based on the results of a study reported by two Israeli researchers. They studied twenty-eight patients who, because of various intestinal problems, were placed on intravenous feedings only. For about seven weeks, the intravenous fluids contained no fat, after which the fluids were supplemented with fat as they normally are. Intraocular pressures were checked on a regular basis before treatment and during both phases of the intravenous feedings. The researchers found that the IOP was significantly lower during the fat-free phase than during the fat-supplemented phase (about three and one-half points, on the average).6 It appears that something about the lack of fat had a lowering effect on IOP.

During the various parts of this study, blood levels of a prostaglandin called PGE2 were also measured. Prostaglandins are substances that our bodies produce from certain fats, and they have a wide array of actions, affecting virtually every bodily function. As mentioned earlier, some prostaglandins have been found to lower IOP, and one form of prostaglandin is now being used in eyedrop form to treat glaucoma. These researchers found that the

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blood levels of PGE2 during the fat-free phase were just half those seen during the fat-supplemented phase. They felt that this drop in prostaglandin levels might have been responsible for the lower IOPs. How can this be if prostaglandin eyedrops, which raise the levels of prostaglandins in the eye, lower the IOP? We can’t say for sure why the IOPs were lowered, but the findings are not necessarily contradictory. Prostaglandins are tricky substances, and their actions can differ depending on their concentration in a given tissue. It is entirely possible that both raising and lowering prostaglandin levels in the eye from their baseline levels could bring the IOP down.

Getting back to the rice diet study, one of the remarkable aspects of that diet was that only about 2.5 percent of the calories it supplied came from fat. This level of fat intake is certainly low enough to create a fatty acid deficiency (there is a requirement for small amounts of fat in the diet), which in turn could lower prostaglandin levels. Therefore, I suggest that the rice diet might lower IOP not because of its low salt content but as a result of its extremely low fat content. Naturally, this is only an educated guess, but further studies in this area could provide some answers. The rice diet does not appear to be nutritionally adequate on a long-term basis, and I definitely don’t recommend your trying it on your own. It would be interesting, however, to see whether diets that are not quite so stringent might also have a favorable effect on the IOP.Vegetarian diets deriving about 10 percent of their calories from fat have enjoyed much success in lowering blood cholesterol levels and reversing coronary heart disease, so perhaps we should give them a try in glaucoma patients as well.

Blood Flow, Omega-3 Fatty Acids, and Ginkgo Biloba

Current glaucoma treatment involves lowering the IOP, but trying to preserve the optic nerve by other means, such as improving blood flow (circulation) to the optic nerve and to the area around it, may be the next great advance. Some studies have compared the

blood viscosity in patients with glaucoma to that of people without glaucoma. Viscosity can be thought of as the “thickness” of the blood. Blood with high viscosity travels more

slowly through small blood vessels than does blood of lower viscosity. Thus, circulation might be impaired when blood viscosity is high. These studies

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have found that patients with glaucoma, including the low-tension variety, have blood with significantly higher viscosity than people with normal eyes or people with elevated IOP but no sign of optic nerve damage.7,8 This suggests why some people with elevated IOP may develop optic nerve damage while others do not.

The most common reasons why some people have a high blood viscosity are a very high red blood cell count or very high levels of proteins in the blood. However, another factor that can play a role is the flexibility of red blood cells, which we call erythrocyte deformability.

When the blood cells are able to “flex” more easily, they are able to flow more easily through tiny blood vessels. Taking dietary supplements of omega- 3 polyunsaturated fatty acids (a type of building block of fat) causes a significant lowering of blood viscosity, apparently by increasing the erythrocyte deformability. Flaxseed oil and fish oils are especially rich in these fatty acids. Therefore, consuming these oils may lower blood viscosity and improve circulation to the optic nerve and elsewhere.

Eskimos, whose diets are very rich in these omega-3 fatty acids, have an extremely low incidence of open angle glaucoma, and this fact has led some people to speculate that the omega-3 fatty acids are protective in this respect. However, many other tribes of Native

Americans, whose diets are much lower in omega-3 fatty acids than those of Eskimos, also have an extremely low incidence of open angle glaucoma. Therefore, it is likely that the low incidence in Eskimos has a genetic basis.

The use of omega-3 fatty acid supplements in patients with glaucoma has never been evaluated in any formal study. Nevertheless, the possibility of protecting the optic nerve in glaucoma patients in this manner is intriguing. Omega-3 fatty acid supplementation for other conditions, such as heart disease and rheumatoid arthritis, has been studied to some degree, but the longterm effects of such supplementation, both good and bad, remain to be determined.

Scientists are now beginning to produce pure preparations of long-chain omega-3 fatty acids, for example, from bacteria or algae, so this type of supplementation may become a reality, allowing people to avoid unwanted fatty acids and other substances present in the fish oils, the most common source

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of omega-3 fatty acids. Since questions remain about the long-term safety of fish oil and other omega-3 fatty acid supplements, however, I do not recommend their use at present.

Another substance that has been shown in many studies to lower blood viscosity is an herbal extract of the plant ginkgo biloba. This extract, which contains many components, has already been under consideration as a possible aid to glaucoma treatment because of the

potent antioxidants in it. (Antioxidants may help protect the optic nerve, although this is unproven.) This extract also contains bilo-

balide, a substance that may help protect nerve tissue from damage. But the extract’s main value may be its ability to increase circulation to areas that need it. A recent study showed that taking ginkgo biloba causes a significant increase in blood flow through the ophthalmic artery (the artery that supplies blood to the eye).9 Ginkgo biloba is one of the most frequently prescribed medications in Germany and France, where it has been found effective in improving mental functioning in the elderly, reducing dizziness and tinnitis (ringing in the ears), and lessening the symptoms of claudication (inability to walk more than a short distance because of poor leg circulation).

Ginkgo biloba’s lowering of blood viscosity may be the means by which it increases blood flow to the eye and other organs. Ginkgo biloba is remarkably free of side effects, but the effects of long-term use have not been fully evaluated. Because it has a mild effect on platelets, the tiny fragments in the blood that prevent bleeding, it should not be used in people who have bleeding tendencies or in people who take the drug warfarin (Coumadin), which affects blood clotting. Actually, this effect on blood platelets could in itself help improve circulation. Although sold by prescription in Europe, ginkgo biloba (Ginkgold and others) is available as an over-the-counter supplement in the United States. Ginkgo biloba appears to have great promise in the treatment of glaucoma, especially the low-tension variety, in which the amount of blood flow to the optic nerve may be critical.

Finally, there is evidence that both exercise and a high-fiber, low-fat diet can lower blood viscosity. In particular, vegetarians, who abstain from beef, fowl, and fish, have been found to have significantly lower blood viscosities than meat eaters, including people who consume animal flesh less than once a week. Exercise and the rice diet, a form of high-fiber, low-fat vegetarian diet,

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have already been discussed as ways of lowering IOP, but their effects on blood viscosity represent another mechanism by which they may protect the optic nerve in people with glaucoma. Whether a low-fat vegetarian diet can help keep your pressures down or retard the progression of your glaucoma remains to be seen, but such a diet is certainly associated with benefits from a general health standpoint.

Glaucoma Surgery

Angle-Closure Glaucoma

Normally, we think of surgery as a last resort. However, for angle-closure glaucoma, it is the treatment of choice. When a person presents with the red, painful eye and extremely high pressures of acute angle-closure glaucoma, the first order of business is to “break” the attack.

Pilocarpine and other pressure-lowering drops are instilled in the involved eye, and substances called osmotic agents are given either by mouth or intravenously. These sub-

stances enter the bloodstream and tend to draw fluid out of the eye, a process that breaks the attack most of the time. Once the attack is broken, we generally let the eye “cool” down for several days before performing an iridotomy, the creation of a small hole in the iris of the eye. This hole is usually created with a laser, either an argon laser, which burns a hole in the iris, or a neodymium: YAG laser, which causes a miniexplosion that results in the tiny hole. This hole allows fluid to travel from the area behind the iris to the area in front, thereby bypassing the pupil and deepening the anterior chamber of the eye and allowing the angle to open up. In addition, an iridotomy is usually performed on the other eye as well. Why? Because both eyes usually have the same shape and structure, and if an attack of acute angle-closure glaucoma has occurred in one eye, there is a good chance it will occur in the other. This type of preventive treatment is important, because an attack of acute glaucoma can sometimes cause irreversible damage to the eye.

Occasionally, we may even perform a laser iridotomy before an attack of glaucoma has ever occurred. For example, if a person who is found to have narrow angles on examination also has a history of occasional eye pain and

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