Diseases of the eye leading to blindness are almost exclusively a function of aging. But certain risk factors make us age faster. There are genetic dispositions for developing eye diseases (1), and in these cases control of possible risk factors is extremely important. Today age-related macular degeneration (ARMD) is the most common disease leading to permanent blindness. The number of seniors getting this disabling disease will increase, as the average lifespan is getting longer. The disease is located to the retina, which is the thin transparent layer of nerve tissue that forms the innermost coat of the eye.
The retina is continuous with the optical nerve leading electrical impulses to the posterior part of the brain. In the retina light energy is transformed into electrical impulses by conformational changes of the light-sensitive protein rhodopsin. The omega-3 fatty acid docosahexaenoic acid (DHA) plays an important part in the generation of these impulses, which are later decoded in the visual cortex of the brain making us perceive what we are casting our eyes on.
The cause of ARMD is unknown, but smoking, high intake of saturated fat and cholesterol as well as other cardiovascular risk factors like diabetes and hypertension have shown statistically associations with development of the disease.
Frequent sunlight exposure throughout life is another risk factor.(2) It has been claimed that chronic use of pharmaceuticals could increase the risk of getting ARMD, but this could not be demonstrated in the large Beaver Dam Eye Study.(3) Interestingly, populations with a high intake of fish, such as Japan and Iceland, have a low incidence of ARMD. The retina of the eye is rich in the omega-3 DHA, and low ARMD rates could be related to the heavy diet of fatty fish in those countries.
Smith et al (4) examined 3,654 individuals older than 49 years in order to reveal clinical signs of ARMD. At the same time dietary questionnaires were collected to correlate the intake of certain nutrients with the occurrence of the disease. 229 of the participants were found to have clinical signs of ARMD in different stages of development. Correlation with the different dietary intake of nutrients among the participants in the study clearly showed that a regular intake of fish prevented development of ARMD while a high intake of saturated fat and cholesterol predisposed to a higher risk of contracting the disease.
In another study, the large Nurses Health Study from Boston, where 42,743 women and 29,746 men were followed for almost 10 years, 567 developed ARMD.(5) Fat intake in the study was assessed by a food-frequency questionnaire. As in the study by Smith, total fat intake positively correlated with increased risk of getting the disease, while a high intake of fish was associated with a 35% lower risk compared to those who only seldom ate fish.
Obviously DHA has important functions in the retina. Premature born children not supplemented with DHA have slower development of visual acuity compared to those given this essential fatty acid.(6) Experiments on rat retina have demonstrated that DHA prevents damages of oxidative stress, an important factor related to aging.(7) Another experiment on monkeys has shown that animals given omega-3 fatty acids may improve nutritional utilization in the retina and at the same time reduce negative effects of oxidative damage.(8) Several studies have been presented using antioxidants to prevent oxidative damage. While vitamin E alone has not demonstrated any positive effects, the combination of antioxidants and zinc in a large controlled study slowed the progression of ARMD.(9)
Earlier this year a scientific meeting in Paris discussed the scientific basis for using DHA-enriched omega-3 supplements for prevention and treatment of ARMD.(10) There was a general agreement that the scientific basis for using DHA was present and preparations are ongoing for a large controlled clinical study in France using a DHA-based nutritional supplement.
The development of age related degenerative diseases such as cardiovascular disease, Alzheimer's disease, and maculopathy probably begins decades prior to the presence of symptoms. In fact early stages of cardiovascular disease have been documented already in young adults. It is therefore important for the individual to induce measures to prevent these disabling diseases. Conclusions from epidemiological studies and animal studies should be treated cautiously and positive results should be tested in controlled clinical trials. However based on the two large epidemiological studies presented above, there is firm evidence for the positive effects of increasing the intake of fish for prevention of ARMD.
The principle of prophylactic treatment with omega-3 fatty acids should be introduced early in life to prevent the development of degenerative diseases, not least ARMD, which could shorten life expectancy and severely reduce quality-of-life.
- Musarella MA. Molecular genetics of macular degeneration. Doc Ophtal Advances in ophthalmology 2001;102:165-177
- Cruickshanks KJ, et al. Sunlight and the 5-years incidence of early age-related maculopathy: the Beaver Dam eye study. Arch Ophtalmol 2001;119:246-250
- Klein R, et al. Medication use and the 5-year incidense of early age-related maculopathy. Arch Ophtalmol 2001;119:1354-1359
- Smith W et al. Dietary fat and fish intake and age-related maculopathy
Arch Ophtalmol 2000;118:401-404
- Cho E et al. Prospective study of dietary fat and the risk of age-related macular degeneration
Am J Clin Nutr 2001;73:209-218
- Neuringer M. Infant vision and retinal function in studies of dietary long-chained polyunsaturated fatty acids. Am J Clin Nutr 2000;71:256-267
- Rotstein N, et al. Protective effect of docosahexaenoic acid on oxidative stress-induced apoptosis of retina photoreceptors. Invest Ophtalmol & Visual Sci 2003;44:2252-2259
- Elner VM. Retinal pigment epithelial acid lipase activity and lipoprotein receptors: effects of dietary omega-3 fatty acids. Transactions Am Ophtalmol Soc 2002;100:301-308
- Frennesson C, et al. Age-related macular degeneration-new possibilities for prophylactic measures. Lakartidningen 2002;99:3194-3197
- Micronutrition en ophtalmologie: Lipides et DMLA. Paris13 juin, 2003. Chauvin/Bausch & Lomb