Alternative Medicine Review 2001 (Apr); 6 (2): 141–166 ~ FULL TEXT
Kathleen A. Head, ND
Introduction
Part one of this article was published in the October 1999 issue of
Alternative Medicine Review and discussed nutritional and botanical approaches
to conditions of the retina. This second part covers alternative treatments
for nonretinal disorders: senile cataracts, diabetic cataracts, and chronic
open-angle glaucoma.
A large percentage of blindness in the world is nutritionally preventable. 1
The author of this comment was referring primarily to the use of vitamin
A to prevent corneal degeneration associated with a vitamin A deficiency;
however, there is considerable evidence that many other eye conditions,
which are leading causes of vision impairment and blindness, also may be
preventable with nutritional supplementation, botanical medicines, diet,
and other lifestyle changes. In addition, a number of nutrients hold promise
for the treatment of already existing cataracts and glaucoma.
Senile Cataracts
Senile cataracts are the leading cause of impaired vision in the United
States, with a large percentage of the geriatric population exhibiting
some signs of the lesion. Over one million cataract surgeries are performed
yearly in this country alone. 2 Cataracts
are developmental or degenerative opacities of the lens of the eye, generally
characterized by a gradual painless loss of vision. The extent of the vision
loss depends on the size and location of the cataract. Cataracts may be
located in the center of the lens (nuclear), in the superficial cortex
(cortical), or in the posterior subcapsular area. Cataracts are also classified
according to their color, which is consistent with location and density
of the cataract. Pale yellow cataracts are typically slight opacities of
the cortex, subcapsular region, or both; yellow or light brown cataracts
are consistent with moderate to intense opacities of the cortex, nucleus,
or both; and brown cataracts are associated with dense nuclear cataracts. 3
Diagnosis
Symptoms include near vision image blur, abnormal color perception,
monocular diplopia, glare, and impaired visual acuity, and may vary depending
on location of the cataract. For example, if the opacity is located in
the center of the lens (nuclear cataract), myopia is often a symptom, whereas
posterior subcapsular cataracts tend to be most noticeable in bright light. 4
Ophthalmoscopic examination is best conducted on a dilated pupil, holding
the scope approximately one foot away. Small cataracts appear as dark defects
against the red reflex, whereas a large cataract may completely obliterate
the red reflex. Once a cataract has been established, a referral for slit-lamp
examination, which provides more detail on location and extent of opacity,
is recommended.
Specific Nutrients and Prevention of Cataracts
Oxidation of lens proteins is part of the pathophysiology of cataracts.
Therefore, it is no surprise that antioxidants may help prevent the formation
of cataracts.
Carotenes and Vitamin A: Epidemiological Evidence
Levels of nutrients, including carotenoids, have been examined in human
cataractous lenses after extraction using high performance liquid chromatography.
Vitamins A and E and the carotenoids lutein and zeaxanthin were found.
The newer, epithelial/outer cortex layer had more carotenoids, tocopherol,
and retinol (approximately 3-, 1.8-, and 1.3-fold higher, respectively)
than the older, inner cortex/nuclear portion.20 Other studies have quantified
significant levels of lutein, zeaxanthin, and alpha- and gamma-tocopherol
in the lens. 21
A prospective study of the effect of carotenes and vitamin A on the
risk of cataract formation was conducted as part of the Nurses' Health
Study. A total of 77,466 female nurses, ages 45-71 years, were included
in the study, which involved food-frequency questionnaires over a 12-year
period. After other risk factors were controlled for, including smoking
and age, those in the highest quintile for consumption of lutein and zeaxanthin
had a 22-percent decreased risk of cataract extraction compared with those
in the lowest quintile. 22
Another cohort of the Nurses' Health Study followed 50,823 women, ages
45-67, for eight years and found women in the highest quintile of vitamin
A consumption had a 39-percent lower risk of developing cataracts compared
to women in the lowest quintile. 23
In a similar study of male health professionals in the United States,
36,644 participants, ages 45-75 years, were followed for eight years with
periodic dietary questionnaires. Men in the highest quintile for lutein
and zeaxanthin intake had a 19-percent decreased risk of cataract extraction
when smoking, age, and other risk factors were controlled for. 24
Neither the women nor the men demonstrated a decreased risk of cataract
with intakes of other carotenoids (a-carotene, b-carotene, lycopene, or
beta-cryptoxanthin). It is hypothesized the protective effect of the carotenoids
may be due to quenching reactive oxygen species generated by exposure to
ultraviolet light. 25
The Beaver Dam Eye Study examined risk for developing nuclear cataracts
in 252 subjects who were followed over a five-year period. Only a trend
toward an inverse relationship between serum lutein and cryptoxanthin and
risk of cataract development was noted. 26
Vitamin E: Animal, Epidemiological, and Clinical
Studies
As a fat-soluble antioxidant, it is reasonable to predict a positive
role for vitamin E as a cataract preventive in the lens cell membrane.
Animal, epidemiological, and clinical studies help confirm this hypothesis.
A placebo-controlled animal study found 100 IU d-alpha-tocopherol injected
subcutaneously prevented ionizing radiation damage to the lens, which did
occur in rats not supplemented with vitamin E. 27
Two other animal studies using vitamin E instilled in the eyes as drops
confirmed the preventive effect of vitamin E, at least when used topically. 28,29
Several human studies have found low levels of vitamin E intake are
associated with increased risk for cataract development. An epidemiological
investigation examined self-reported supplementary vitamin consumption
of 175 cataract patients compared to 175 matched individuals without cataracts.
The cataract-free group used significantly more vitamin E (p=0.004) and
vitamin C (p=0.01) than the cataract group, resulting in at least a 50-percent
reduction in cataract risk in the supplemented group. 30
An Italian study compared 207 patients with cataracts to 706 control subjects
in a hospital setting. Vitamin E, in addition to a number of other nutritional
factors, was associated with a decreased risk for cataract. 8
The Vitamin E and Cataract Prevention Study (VECAT) is a four-year,
prospective, randomized, controlled trial of vitamin E versus placebo for
cataract prevention in a population of healthy volunteers, ages 55-80 years. 31
Although results are still pending, data was collected on prior use of
vitamin E and incidence of cataract in 1,111 participants. A statistically
significant relationship was found between past vitamin E supplementation
and prevention of cortical cataract but not nuclear cataract. 32
The Lens Opacities Case-Control Study was designed to determine risk
factors for cataracts in 1,380 participants, ages 40-79 years. Blood chemistry
and levels of vitamin E and selenium were performed on all patients. The
risk of developing cataracts was reduced to less than one-half (odds ratio
0.44 for nuclear cataracts) in subjects with higher levels of vitamin E. 33
Some of these same researchers examined the association between antioxidants
and the risk of cataract in the Longitudinal Study of Cataract. Dietary
intake, use of supplements, and plasma vitamin E levels were assessed on
764 participants. Lens opacities were examined on a yearly basis and the
risk of development of cataract was 30-percent less in regular users of
a multiple vitamin, 57-percent less in regular users of supplemental vitamin
E, and 42-percent less is those with higher plasma levels of vitamin E. 34
In a randomized trial of 50 patients with early cataracts, subjects
were assigned to receive either 100 mg vitamin E twice daily or placebo
for 30 days. There was a significantly smaller increase in the size of
cortical cataracts in the vitamin E group compared to placebo. While increases
of vitamin E were found in both nuclear and cortical lens homogenates after
surgical removal, GSH levels were increased significantly only in those
with cortical cataracts receiving vitamin E. In addition, the malondialdehyde
(MDA) Ñ a measure of oxidative stress Ñ levels and glutathione
peroxidase levels were higher in cortical cataract/vitamin E users than
in the nuclear cataract/vitamin E group. 35
Some conclusions that can be drawn from this study are: (1) vitamin E decreases
oxidative stress in cataractous lenses; (2) part of vitamin E's protective
effect is due to enhancement of GSH levels; and (3) vitamin E seems to
be more protective for cortical than nuclear cataracts, at least in this
short-term study.
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