Introduction
Which one of your five senses would you least like to lose? For most people,
it is their vision. Our sight is so precious and we depend upon it so much that
we can't imagine what life would be like if we could no longer see. Even when
we eat delicious vegetarian food, we "eat" with our eyes: our first
impression of the food comes from its appearance, and a bad first impression
is hard to overcome no matter how good the food tastes. Not surprisingly, the
eye, the delicate and complex end-organ of sight, is influenced by our nutritional
status. Let's look at some common eye problems and see how they relate to our
diets.
Glaucoma and Intraocular Pressure (IOP)
Glaucoma refers to a group of diseases characterized by a progressive loss of
the nerve fibers which make up our optic nerves. Glaucoma can result from other
eye problems, but we will limit the discussion here to chronic open-angle glaucoma,
the most common type. The main risk factor for glaucoma is an elevated intraocular
pressure (IOP), the fluid pressure inside the eye, which is different from blood
pressure. Some feel that the blood circulation to the optic nerve also plays
a role. Nevertheless, the only treatment we have for glaucoma is to lower the
IOP. Normally, this is accomplished by drugs in the form of eye drops or pills,
and laser or conventional surgery can be performed as a last resort. But drugs,
even in eye drop form, have side effects. Therefore, let's explore non-drug,
non-surgical alternatives for the lowering of IOP.
A potentially effective therapy is exercise training. One study showed that
regular aerobic exercise on an exercise bike lowered the average IOP in patients
suspected of having glaucoma by 4-1/2 mm, or about 20%, a significant amount.[1]
Jogging, however, might raise IOP in people who have a less common form of glaucoma
called pigmentary glaucoma.
Effects of Diet on IOP
Both eating and drinking can affect IOP. Drinking a large amount of liquid all
at once can raise IOP and should be avoided. Dr. Carlo Pissarello published
studies in 1915 [2] which showed that the IOP falls right after eating and tends
to be highest just before the next meal. This may explain why, in the diurnal
variation of IOP, it tends to be highest early in the morning, since we have
been fasting overnight. An interesting question would be whether a "grazing"
type of diet, which seems to help lower cholesterol and facilitate weight loss,
would help keep IOP down. When a glaucoma patient goes to the ophthalmologist
to have a pressure check, it might be a good idea occasionally to do it at a
time when the IOP is likely to be at its zenith -- early in the morning before
eating breakfast or else just before supper or lunch.
Can any particular diet lower IOP? The answer appears to be yes. In the late
1940's, Dr. Frederick Stocker and associates studied what they called the "rice
diet." This diet had previously proved very effective in lowering blood
pressure. The diet was limited to rice, sugar, fruit, and fruit juices, supplemented
by vitamins and iron. It contained about 2,000 Calories with 20 gm of protein,
5 gm of fat, 460 gm of carbohydrate, 0.2 gm of sodium, and 0.15 gm of chloride.
They found that "reductions [of IOP] of 5 or 7 mm, persisting over long
periods, were not uncommon."[3] A reduction of this magnitude is considered
quite significant for a glaucoma patient and is about the amount that one would
expect to result from a successful laser treatment. The researchers were not
sure why the diet was effective but speculated that the very low sodium and
chloride content somehow influenced fluid secretion into the eye. I was able
to speak with the third author, Dr. James Clower, who was a resident at Duke
at the time, and who is still practicing ophthalmology in Florida. He said that
no follow-up studies had been done, but he laughingly commented that perhaps
Seventh-day Adventists would have the best pressures! [Note from the editors:
Many Seventh-day Adventists follow a vegetarian diet. Perhaps Dr. Clower felt
this diet would be lower in protein and sodium; although this is not necessarily
true.]
A more recent study out of Israel followed people who were placed on intravenous
feedings because of intestinal problems.[4] When the intravenous fluids were
fat-free, IOP's were significantly lower than when fat was included. Since certain
fat-derived blood chemicals called prostaglandins were greatly reduced in the
fat-free phase, and since prostaglandins are known to influence IOP, they theorized
that this was the reason for the effect they were observing. Therefore, it may
have been the ultra-low fat content of the "rice diet" which was responsible
for the lowering of IOP. Certainly, further studies on low-fat diets would be
welcome. (Caution: the rice diet as described is nutritionally inadequate and
should not be attempted on your own.)
Age-Related Macular Degeneration (AMD)
Age-related macular degeneration (AMD) is the leading cause of loss of vision
in people over the age of 55. The degeneration involves the central part of
the retina where the best vision is, sparing peripheral vision. In a small minority
of people with this condition, abnormal blood vessels can grow behind the retina
where they can leak and bleed. If this is detected before the blood vessels
reach the exact center of the retina, the vessels can sometimes be obliterated
with laser.
Zinc and Copper Supplementation
Nutritional therapy is now all the rage in AMD. Zinc is the most abundant trace
mineral in the eye, and a study published in 1988 showed that oral zinc sulfate,
100 mg twice a day, might slow the progression of AMD.[5] A plethora of zinc/antioxidant
supplements has since appeared on the market. The products, promoted by drug
companies and often sold by ophthalmologists, are now heavily used.
In examining whether high-dose zinc supplementation is justified, we encounter
some problems and uncertainties. First, only this one study has been published
in a peer-reviewed journal. Generally, a study, no matter how well done, should
be confirmed by additional studies. Second, only one dosage of zinc was studied.
Perhaps a much smaller dose would also be effective. Third, large amounts of
zinc can impair the immune system by affecting white blood cell function.[6]
This was studied using 150 mg of elemental zinc twice a day. Whether the amount
of zinc currently being prescribed for AMD can impair immune function remains
to be determined. Our immune systems protect our bodies against cancer and infections.
Fourth, zinc in high doses can interfere with the absorption of other minerals,
such as copper and iron.
A copper deficiency anemia can occur,[7] and copper deficiency has also been
theorized to be a cause of atherosclerosis (hardening of the arteries), which
results in heart disease.[8] To lessen that risk, the supplements generally
contain some copper. We cannot be sure, though, that they contain enough copper
to prevent copper deficiency. On the other hand, some have speculated that perhaps
it is not the zinc which is helping the AMD but a copper deficiency induced
by the high zinc dose. (Subjects in the AMD study did not take copper along
with the zinc.) If that is the case, then taking copper with the zinc may nullify
the beneficial effect initially observed.
As you can see, there are no clear cut answers at present. We eagerly await
further studies.
Antioxidant and Herb Therapies
Oxidation of the polyunsaturated fatty acids found in the membranes of the rods
and cones of the retina has been proposed as a possible cause of AMD. This is
the rationale for the use of antioxidant vitamins, such as beta-carotene and
other carotenoids, vitamin C, and vitamin E. One recent study did show, in fact,
a reduced risk of visual loss from the bleeding from AMD in people with high
blood levels of these antioxidants.[9] Another study showed that higher blood
cholesterol levels seemed to reduce the risk of the dry, or non-bleeding, form
of AMD.[10] The authors did not have a good explanation for this phenomenon.
My theory is that since beta-carotene and vitamin E travel in the blood with
cholesterol, people who are genetically predisposed to lower cholesterol levels
carry a lesser amount of these antioxidants to their tissues. Vegetarians, however,
have a higher antioxidant/cholesterol ratio than non-vegetarians [11, 12], and
so they probably would not share the higher risk associated with low cholesterol
levels. Again, studies are needed.
A small, controlled French study found that ginkgo biloba extract (50:1) had
a beneficial effect on the vision of patients with AMD.[13] Ginkgo is a most
interesting herb with many potential applications. It contains unique compounds
called ginkgolides which are potent inhibitors of platelet-activating factor
(PAF), a body chemical involved in inflammatory processes. PAF inhibitors have
been shown to combat inflammation and to increase blood flow to areas with reduced
circulation. The ginkgo extract also has antioxidant properties. Whether it
was one component or a synergistic effect among several components of this extract
which had the beneficial effect is not certain. In any case, a much larger study
needs to be done. Ginkgo should not be used by anyone who takes Coumadin or
who has a bleeding tendency. Also, PAF inhibitors may impair natural killer
cell (a type of white blood cell) function somewhat. Herbs, like any drug, should
be used only with the consent of your physician.
Cataracts, Diabetes and Retinopathy
Cataract refers to a cloudiness of the eye's lens. It is caused by changes in
the protein which composes the lens. Since the lens and the fluid surrounding
it are high in antioxidants, it is thought that the antioxidants may help the
lens maintain its clarity. People with higher than average intakes of beta-carotene,
vitamin C, and vitamin E appear to have a reduced risk of cataract. More definitive
studies are now being conducted.
Diabetes increases the risk of cataract, but it can also cause more severe visual
loss by affecting the blood vessels in the retina, a condition called retinopathy.
The walls of the blood vessels are weakened, causing them to leak, which blurs
vision. Abnormal, fragile blood vessels may also grow in. They can bleed into
the eye, causing severe problems. Type II diabetes, the milder adult-onset form,
is virtually absent in populations consuming high fiber diets.[14] Thus, a low-fat,
high fiber vegetarian diet may be the best way to prevent or reverse this illness.
Type I diabetes, the juvenile insulin-dependent form, may be triggered by a
reaction to a cow's milk protein.[15] A high fiber, vegetarian-type diet can
lower insulin requirements and improve control, which may retard the progression
of retinopathy. (Caution: diabetics should not change their diets without the
consent of their physicians.)
Both types of diabetes can cause retinopathy. One study showed that diabetics
without retinopathy had significantly higher carbohydrate and fiber intakes
than did diabetics with retinopathy.[16] Furthermore, dietary or other treatment
which aggressively lowers blood cholesterol levels can sometimes clear up the
fat-rich leakage called hard exudates which many diabetics develop in their
retinas.[17] This could conceivably eliminate the need for laser treatments
in some individuals. In a small pilot study, an extract of the herb ginkgo biloba
(see above) showed some promise in improving vision in patients with very mild
retinopathy.[18]
The Ideal Diet for Good Eye Health
To summarize, the ideal nutritional approach to maintain the health of the eye
would appear to be a high fiber, high carbohydrate, high antioxidant, low fat,
low protein type of diet, typified by -- you guessed it -- a vegetarian diet.
Jay Lavine, M.D., is an ophthalmologist and resides in Phoenix, Arizona.
References
1. Passo MS, Goldberg L, Elliot DL, Van Buskirk EM. Exercise training reduces
intraocular pressure among subjects suspected of having glaucoma. Arch Ophthalmol
1991;109: 1096-8.
2. Pissarello C. La curva giornaliera della tensione nell'occio normale e nell'occhio
glaucomatoso e influenza di fattori diversi (miotici, iridetomia, irido-sclerectomia,
derivativi, pasti) determinata con il Tono-metro di Schiotz. Ann Ottalmol 1915;44:
544-636.
3. Stocker FW, Holt LB, Clower JW. Clinical experiments with new ways of influencing
intraocular tension. I. Effect of rice diet. Arch Ophthalmol 1948; 40:46-55.
4. Naveh-Floman N, Belkin M. Prostaglandin metabolism and intraocular pressure.
Br J Ophthalmol 1987; 71:254-6.
5. Newsome DA, Swartz M, Leone NC, Elston RC, Miller E. Oral zinc in macular
degeneration. Arch Ophthalmol 1988; 106:192-8.
6. Chandra RK. Excessive intake of zinc impairs immune responses. JAMA 1984;
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7. Patterson WP, Winklemann M, Perry MC. Zinc-induced copper deficiency: megamineral
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11. Pronczuk A, Kipervarg Y, Hayes KC. Vegetarians have higher plasma alpha-tocopherol
relative to cholesterol than do nonvegetarians. J AM Coll Nutr 1992; 11:50-5.
12. Malter M, Schriever G, Eilber U. Natural killer cells, vitamins, and other
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seniles" par l'extrait de Ginkgo biloba. Presse Med 1986;15:1556-8.
14. Trowell HC. Dietary-fiber hypothesis of the etiology of diabetes mellitus.
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trigger of insulin-dependent diabetes mellitus. N Engl J Med 1992; 327: 302-7.
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with and without retinopathy. Am J Clin Nutr 1989;50:728-30. 17. Gordon B, Chang
S, Kavanagh M, et al. The effects of lipid lowering on diabetic retinopathy.
Am J Ophthalmol 1991;112: 385-91.
18. Lanthony P, Cosson JP. Evolution de la vision des couleurs dans la retinopathie
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671-4.
For Questions or Comments
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