Normal vision occurs when light is focused directly on the retina rather than in front or behind it. This is called 20/20 vision, and it means that the person can clearly see any object that is 20 feet away. Seeing objects both near and far clearly does not mean a person has perfect vision. There are other important vision skills such as peripheral vision, eye coordination, depth perception, focusing ability, and color vision that should be present to make up overall visual ability.1
There are two groups of eye disorders: vision problems and eye diseases that affect the physical health of the eye and can cause blindness. Early detection and treatment of eye diseases can prevent vision loss; therefore, annual eye examination and nutrition are very important to keep the eyes healthy. In addition, many other head and neck diseases such as carotid artery blockage can be diagnosed by regular eye examinations, thus saving lives.1
The National Eye Institute (NEI) has reported that more than 9 million Americans have age-related macular degeneration (AMD), one of the leading causes of vision loss for people over 60 years. More than 22 million people have cataracts and about 2.2 million have glaucoma, and diabetic retinopathy affects the vision of more than half of the 25.8 million people age 18 and older who have diabetes. An NEI survey has ranked vision loss ahead of memory and hearing loss as measured by the number of people affected. But it indicates that losing eyesight is not a normal part of aging.2
The importance of good nutrition increases drastically for several reasons as we age. The body needs more vitamins and nutrients to keep it working healthily and properly, and it has a harder time digesting and processing the vitamins that we acquire in our regular diet. Since the eyes are probably the most important organ connected to the senses, certain vitamins and nutrients can help protect the eye from age-related diseases such as AMD.2
Many causes of blindness are preventable through timely examination and treatment. In this article, we will briefly review eye diseases and vision conditions, the importance of early treatment, and the role of certain vitamins and nutrients in maintaining eye health.
EYE DISORDERS
There are four major diseases that affect the eye and can lead to blindness.
Cataracts: Cataracts, or clouded lenses, affect vision and are very common in older people. Cataracts affect over 40% of people between 50 and 65 years, over 60% of people older than age 66, and up to 90% of people over the age of 90. Clouding can be semitransparent or completely opaque, which causes total blindness. Common symptoms of cataracts are blurry vision, colors that seem faded, glare, poor night vision, double vision, and frequent changes in prescriptions for eyeglasses.1,2
The chance of getting cataracts can be greatly reduced by taking certain vitamins before the cataracts start to appear. However, in most cases surgery is an option that involves removing the cloudy lens and replacing it with an artificial lens. Wearing sunglasses and a hat with a brim to block ultraviolet sunlight may help to delay cataracts.1
Glaucoma: Glaucoma damages the eye’s optic nerve (see FIGURE 1) and is an age-related eye disease that affects about 1 in every 200 people. The optic nerve damage is the result of increased intraocular pressure (IOP) in and around the eye. Glaucoma has no early symptoms and usually goes undetected until it is fairly advanced. Loss of at least some vision is almost guaranteed if preventive measures and comprehensive eye examinations are not taken. Glaucoma is a leading cause of blindness among African Americans and Hispanics. African Americans experience this eye disease at a rate of three times that of whites. Studies as early as the 1950s showed that certain vitamins could decrease the IOP in the eye for a short time, and that taking certain eye vitamins regularly could help you keep a healthy IOP indefinitely. In this case, prescription eye drops and surgery are the options. There is no cure for glaucoma, although there has been some increased understanding of the genetics of glaucoma recently, including the discovery of genes associated with the disease.1,2
Age-Related Macular Degeneration: This disease affects about 9 million people in the United States alone. It is a disease that destroys the sharp, central vision needed to see objects clearly. It affects all daily activities including reading, driving, and watching television. AMD is a disease in which certain deposits or blood vessels under the macula can damage the eye rods and cause cells in the macula to die. In some cases, AMD advances so slowly that people do not notice major vision problems. There are two kinds of AMD: wet (neovascular) and dry. Wet AMD (the more serious form) occurs when abnormal blood vessels behind the retina start to grow under the macula. Dry AMD occurs when the light-sensitive cells in the macula slowly break down. Although there is no cure for AMD, early detection may make treatment more successful. The NEI has conducted research that shows certain combinations of vitamins and minerals can greatly reduce the chances of getting macular degeneration (more on how vitamins work below).2
The NEI recently concluded the first year of a 2-year clinical trial to compare the efficacy and safety of two VEGF (vascular endothelial growth factor) inhibitors used to treat wet AMD. The two drugs, which are intravitreal (injected into the eye), are ranibizumab (Lucentis) and bevacizumab (Avastin). Results show that both drugs are equally effective in treating AMD.3
VEGF inhibitors prevent angiogenesis and increases in vasculature permeability and inflammation under the macula. Intravitreal injection of these drugs has slowed down the course of this disease.3
The FDA has recently approved a third drug, VEGF Trap-Eye or aflibercept (Eylea), for the treatment of wet AMD. This drug is a fusion protein that acts as a decoy VEGF receptor, competing for binding of VEGF. It blocks the growth of the abnormal new blood vessels in the eye that cause vascular permeability and edema. The dose is 2 mg (0.05 mL) by intravitreal injection every 4 weeks for 3 months, followed by 2 mg once every 8 weeks thereafter.3
Diabetic Retinopathy: Diabetic retinopathy is the result of diabetes and is another major age-related eye disease affecting the retina, the light-sensitive tissue at the back of the eye; it causes most cases of blindness in U.S. adults. It is treated with surgery or laser surgery. With adequate control of blood sugar, blood pressure, and cholesterol level, and with regular follow-up, blindness from diabetes can be prevented. Loss of vision can literally happen overnight with this disease. In almost every case, if left untreated, damage to the retina can be permanent, causing significant vision loss or blindness. Taking vitamins for eye health is one way to decrease the chance of diabetic retinopathy.1
Common Vision Problems
Nearsightedness (Myopia): Nearsightedness results in blurred vision when the visual image is focused in front of the retina, rather than directly on it. It occurs when the physical length of the eye is greater than the optical length. For this reason, nearsightedness often develops in the rapidly growing school-aged child or teenager and progresses during the growth years, requiring frequent changes in glasses or contact lenses. A nearsighted person sees near objects clearly, while objects in the distance are blurred. Treatment helps to focus light on the retina through the use of corrective lenses or refractive surgery. LASIK surgery reshapes the curvature of the cornea.2
Farsightedness (Hyperopia): Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is frequently present from birth, but children can often tolerate moderate amounts without difficulty and most outgrow the condition. Most young people do not need corrective lenses, but as natural lenses become less flexible, eyeglasses or contacts are necessary to improve vision. Additional treatment is conductive keratoplasty (CK), which use radiofrequency energy to apply heat to tiny spots around the cornea.2
Astigmatism: In astigmatism, the cornea is more oval than round. This will not allow the eye to focus clearly. This issue is accompanied by near- and farsightedness. Current treatments adjust the cornea’s uneven curvature through corrective lenses or refractive surgery. A procedure called orthokeratology, which involves wearing rigid contact lenses for several hours a day, will improve the uneven curvature. After that, the patient wears lenses less frequently to maintain the new shape. Unfortunately, if the treatment is stopped, the eyes return to their former shape.2
Other Eye Diseases
Eye infections, eye injuries, eye tumors, dry eye, and lazy eye are other eye problems that are beyond the scope of this article.
Eye Vitamins and Minerals
In a nationwide clinical study by NEI, an experimental combination of three antioxidant vitamins (C, E, and beta-carotene) and the minerals zinc and copper reduced the advancement of AMD by 25% and the risk of moderate vision loss by 19%. These results were of public health significance and were published in 2001. Several years later, a double-blind follow-up to this study determined how high doses of antioxidant and fish oil supplements affect the risk of advanced AMD, the need for cataracts surgery, and moderate vision loss. The results of this study indicated that adults eating kale, mustard greens, collard greens, raw or cooked spinach (vegetables high in lutein and zeaxantine, called xanthophylls), and two antioxidants from beta (the carotene family) were at considerably less risk of developing advanced AMD than those who did not eat them. Also, adults consuming more sources of the omega-3 fatty acids DHA and EPA are at less risk of this disease.2,4,5
Selenium has positive effects on the eyes and also helps the body to absorb both vitamin A and vitamin E, the key vitamins in eye health.
Mechanism of Action
The yellow color of the macular region of the retina is due to the presence of macular pigment, composed of two dietary compounds, lutein and zeaxanthin, and a third, called meso-zeaxanthin. This last one is presumably formed from either lutein or zeaxanthin in the retina. The macular pigments absorb the blue light and protect the underlying photoreceptor cell layer from light damage. There is ample epidemiologic evidence that the amount of macular pigment is inversely associated with the incidence of AMD, an irreversible process that is the major cause of blindness in the elderly. The macular pigment can be increased in the retina by either increasing the intake of foods that are rich in lutein and zeaxanthin or supplementing with lutein or zeaxanthin. Although increasing the intake of lutein or zeaxanthin might prove to be protective against the development of AMD, more studies are needed to demonstrate this.6
Vitamin A
As mentioned, vitamin A has been known to have a beneficial affect in the eye as well as in the rest of the body. Vitamin A was the first vitamin studied in detail for its effects on the eye. The precursor beta-carotene (found in carrots and yellow or orange vegetables) is converted into forms of vitamin A called retinols. Retinols have numerous functions in the body, including assisting the bioelectrical process of vision (preventing loss of night vision), eliminating damaged cells from the body, and helping to prevent dry macular degeneration. Vitamin A palmitate (or retinyl palmitate, 5,000 IU) helps with day-to-day vision.7
As mentioned earlier, the NEI has found direct links between the above vitamins and minerals and eye health. For complete eye health, and to significantly reduce the chances of age-related eye diseases and vision loss, people must take extra supplements specifically engineered for the eyes. Lutein is a carotenoid that is now thought to have more preventive properties than vitamin A at a of dose 5 mg daily.2
Bilberry (Vaccinium myrtillus)
According to the CDC, various colors of fruits and vegetables help to promote optimal health.
As early as the 1940s, World War II pilots claimed that bilberries significantly increased their night vision when conducting night missions. Bilberries are of a darker blue color and are smaller than blueberries. They are also softer and juicier than blueberries, making them difficult to transport. Because of these factors, bilberries are only available fresh in markets and are also more expensive. They are easily distinguished from blueberries because of the way they stain the hands, teeth, and tongue deep blue or purple. Bilberries contain natural antioxidants called anthocyanosides, which, among other properties, strengthen blood cells, significantly reducing hemorrhaging in the eye that can lead to both macular degeneration and diabetic retinopathy. Bilberries are also a good source of chromium, which helps control blood sugar levels and preserves the strength of smaller blood vessels, particularly important for patients with diabetes who are at risk for diabetic retinopathy.8,9
In addition, bilberries contain both vitamin A and vitamin C, which are vital to eye health. Recent studies have shown that bilberries also aid in stabilizing and preventing the deterioration of the collagen in eye tissue, thereby helping to prevent intraocular pressure issues such as occur in the devastating glaucoma. In Scandinavian countries, bilberries are collected from forests. They are eaten fresh or can be made into different jams, pies, and other dishes.7,9
Vitamin B2 has also been used for years in helping to strengthen the cornea through a process called collagen cross-linking. Riboflavin has been shown to stop the onset of the eye disorder keratoconus.7
Comprehensive Dilated Eye Examination
This annual examination is necessary to check for common vision problems and eye diseases that have no early warning signs. The examination includes dilation, tonometry, the visual field test, and the visual acuity test. Dilation allows the physician or the optometrist to find any sign of eye diseases. Tonometry helps to detect glaucoma by measuring eye pressure. Visual field tests measure peripheral or side vision, and visual acuity tests measure how well the person sees at various distances.2
REFERENCES
1. Lambris JD, Adamis AP. Inflammation and Retinal Disease: Complement Biology and Pathology. New York, NY: Springer-Science; 2010:140-167.
2. National Eye Institute. www.nei.nih.gov/eyeclinic and MedlinePlus. www.medlineplus.gov. Accessed August 2, 2012.
3. Aflibercept (eylea) for age-related macular degeneration. Med Lett Drugs Ther. 2012;54(1383):9-10.
4. Bartlett H, Eperjesi F. A randomised
controlled trial investigating the effect of lutein and antioxidant
dietary supplementation on visual function in healthy eyes. Clin Nutr. 2008;27:218-227.
5. Moeller SM, Voland R, Tinker L, et
al; CAREDS Study Group; Women’s Health Initiative. Associations between
age-related nuclear cataract and lutein and zeaxanthin in the diet and
serum in the Carotenoids in the Age-Related Eye Disease Study, an
Ancillary Study of the Women’s Health Initiative. Arch Ophthalmol. 2008;126:354-364.
6. Krinsky NI, Landrum JT, Bones RA. Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye. Ann Rev Nutr. 2003;23:171-201.
7. Christen WG, Liu S, Glynn RJ, et al.
Dietary carotenoids, vitamins C and E, and risk of cataract in women: a
prospective study. Arch Ophthalmol. 2008;126:102-109.
8. Jang YP, Zhou J, Nakanishi K, Sparrow
JR. Anthocyanins protect against A2E photooxidation and membrane
permeabilization in retinal pigment epithelial cells. Photochem Photobiol. 2005;81(3):529-536.
9. Muth ER, Laurent JM, Jasper P. The
effect of bilberry nutritional supplementation on night visual acuity
and contrast sensitivity. Altern Med Rev. 2000;5(2):164-173.
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