Nutrition and the Eye
by Jay Lavine, M.D.
Topics in this article:
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 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.
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) 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.
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.
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.
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]
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.
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'occhio 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; 252:1443-6.
7. Patterson WP, Winklemann M, Perry MC. Zinc-induced copper deficiency:
megamineral sideroblastic anemia. Ann Intern Med 1985; 103:385-6.
8. Klevay LM. The homocysteine theory of arteriosclerosis [letter]. Nutr
Rev 1992; 50:155.
9. Eye Disease Case-Control Study Group. Antioxidant status and
neovascular age-related macular degeneration. Arch Ophthalmol
1993;111:104-9.
10. Klein R, Klein BEK, Franke T. The relationship of cardiovascular
disease and its risk factors to age-related maculopathy: the Beaver Dam
eye study. Ophthalmology 1993;100:406-14.
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 blood components of vegetarian and omnivorous men. Nutr Cancer
1989;12:271-8.
13. Lebuisson DA, Leroy L, Rigal G. Traitement des degen-erescences
"Maculaires 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. Diabetes 1975;24:762-5.
15. Karjalainen J, Martin JM, Knip M, et al. A bovine albumin peptide as a
possible trigger of insulin-dependent diabetes mellitus. N Engl J Med
1992; 327: 302-7.
16. Roy MS, Stables G, Collier B, Roy A, Bou E. Nutritional factors in
diabetics 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 diabetique debutante traitee par extrait de Ginkgo biloba. J
Fr Ophtalmol 1988;11: 671-4.
This article was originally published in the Vegetarian Journal,
published by:
The Vegetarian Resource Group
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E-mail: vrg@vrg.org
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