By Deborah Zelinsky, O.D. Executive Research Director, Mind-Eye Institute
When it comes to nutrition, the eyes have it – literally.
In other words, what you put into your mouth (and thus, stomach) determines what enters your bloodstream. The blood carries oxygen, nutrients, and other needed elements to the retina (lining) of your eye. If the blood fails to deliver proper nourishment, the photoreceptors (rods and cones) of the eye can suffer.
Rods and cones are the photoreceptor cells that provide for eyesight. Each eye contains about six million cones and 120 million rods. Cones are activated in daylight and bright, artificial light, while the eye is dependent on the rods in dim light. If unhealthy particles are circulating in the blood and escape through retinal barriers, they can damage the photoreceptors over time.
Typically, the rods and cones work as a team, with the rods governing peripheral eyesight used for spatial judgment of surroundings, such as shape, size, location, and speed of targets in the background, and the cones are used for seeing sharp details on non-moving targets. A degeneration of the cones, for example, would affect central eyesight and require using peripheral eyesight more, relying on the general glimpsing judgments rather than seeing details with the brain filling in what it thinks is seen. When glimpsing, it is easy to make mistakes. For instance, when using mainly peripheral eyesight, during this time of COVID-19, the word “vacation” can fool the periphery into thinking it reads “vaccination.”
However, it is not simply dependency on one set of photoreceptors more than another that makes poor nutrition so potentially impactful. The retina is composed of brain tissue and is a functioning part of the central nervous system. Only a portion of it is devoted to eyesight. The retina serves as a two-way communication portal between the outside eyesight and internal systems in addition to eyesight centers, such as sleep centers (seen in jet lag), posture centers and mood regulation. Entering light activates chemical signals in the retina which eventually convert into electrical signals and, in turn, control eye movement and visual attention.
Retinal processing impacts physical, physiological, and psychological systems including motor control, biochemical activity, and perception. Just as in cases of brain injury and neurodegenerative disorders like Alzheimer’s and Parkinson’s diseases, improper nutrition can create a toxic environment for retinal tissue and lead to disruption of the delicate balance between central and peripheral eyesight.
When central and peripheral eyesight systems fail to interact appropriately, and sensory systems, especially eyes and ears, fall out of synchronization, impacting internal stress levels, patients become confused about their surrounding environment, have a narrowed perception and awareness, exhibit inappropriate reactions and responses, and experience difficulties with visual skills, such as learning and memory.
Research also indicates that nutritional deficiencies increase a person’s risk for developing eye diseases, most notably macular degeneration, which is a deterioration of the center portion of the retina. In a study published in a 2017 issue of the Proceedings of the National Academy of Sciences, investigators reported finding a link between nutrition and retinal damage. Specifically, authors indicated rodents fed a high glycemic diet – namely, foods that spike blood sugar levels and cause the body to produce more insulin – were more likely to exhibit signs of retinal damage similar to that of patients with a certain type of macular degeneration. Switching the mice to low-glycemic foods delayed or even reversed the accumulation of harmful metabolic particles in the eye, the scientists reported. They concluded that proper nutrition might play an important future role in treatments to prevent progression of the degeneration.
Age-related macular degeneration (AMD) is the leading cause of loss of eyesight in people over age 50. Nearly 2.1 million Americans have late-stage AMD – a number expected to grow as the population ages. Widely recognized studies of nutritional supplementation for AMD were done by the Age-related Eye Disease Study Group (AREDS), which concluded that supplementation with vitamin C, vitamin E, beta-carotene, zinc, and copper slowed its development. The risks of beta-carotene supplements must be carefully considered. A 1994 study in The New England Journal of Medicine found an increased correlation between beta-carotene supplementation and the development of lung cancer in smokers. A systematic review in the International Journal of Cancer by Druesne‐Pecollo, et al., in 2010 found an increased incidence of lung and stomach cancer when beta-carotene was supplemented in smokers and asbestos workers. The study found no significant association with beta-carotene supplementation and cancer prevention in non-smokers, but it is worth noting that beta-carotene toxicity also is linked to yellowing of skin and nails. The AREDS2 study published in Opthalmology in 2012 by Chew, et al., considered supplementation with lutein, zeaxanthin, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and omega-3 containing fish oils. The AREDS2 formula removed beta-carotene due the research concerns noted above regarding beta-carotene supplementation in smokers.
In an earlier study, published in 2005, the authors suggested that “high-fat diets have been overall associated with a number of retinal diseases.” Recently, Agron et al., in 2021 found an increased association of AMD with consumption of saturated, monounsaturated, and unsaturated fats. The study, however, found a decreased incidence of AMD was associated with increased fish and fish oil intake. The information on monounsaturated fats such as olive oil is mixed. Research by Cougnard‐Grégoire et al., in 2016 suggests that a diet rich in olive oil may be protective against AMD. Given the above research on fish oil and olive oil, and a systematic review in 2019 by Chapman et al., which correlated the Mediterranean diet with a decreased incidence of late development of AMD, it seems prudent to advise most people looking to prevent AMD to follow a diet high in fresh, whole vegetables and grains, frequent fish consumption, and minimal amounts of saturated fats and processed foods. A study by Hernandez et al. in 2021 suggests vitamin D may also play a role in AMD. Vitamin D is fat soluble, so testing is important before supplementation. When considering vitamin and mineral supplementation, it is crucial to discuss your needs with a professional who will be able to personalize the recommendation to take into account any medical conditions, medications, lab results, and supplement interactions.
Meanwhile, in research published in 2014 in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, scientists wrote that a low-salt diet protects the retina from vascular changes that threaten eyesight, including abnormal neovascularization – the proliferation of new, fragile blood vessels that can leak and obscure sight – such as occurs in diabetic retinopathy.
But, of course, nutrition is only one factor in general eye health and must be considered as just a component in an overall healthy lifestyle. Because of the prevalence of macular degeneration and other eye disorders in the United States, my advice is multifactorial:
- Develop enhanced usage of your peripheral eyesight as well as central eyesight. Should the macula deteriorate, you will be able to adapt more readily to the peripheral retinal skills, lessening overall stress and accelerate decision-making.
- Consider carefully what you put into your mouth. Eating and drinking are analogous to rubbing creams or ointments on your skin or scalp. The chemicals eventually enter the bloodstream and can cause havoc to the eye, brain, and other structures. Consider minimizing toxin exposure by choosing cleaning products that minimize chemicals, choose glass instead of plastic for food storage, chemical-free personal care products, and organic foods where possible. The Environmental Working Group has a list of the Dirty Dozen and Clean Fifteen foods that will assist in prioritizing which items are most important to purchase organic.
- Eat a wide variety of vegetables and fruits in a wide variety of colors. Strive for eating more non-starchy vegetables at each meal rather than starchy ones.
- Minimize processed foods.
- Consider adopting a Mediterranean style diet, high in fresh vegetables and fruit, including fish, nuts and olive oil, and low in saturated fat, processed carbohydrates, and sugar.
- Develop a personalized supplement plan with your medical and nutrition professionals.
- Have routine eye check-ups to assess your use of peripheral eyesight and the stability of the linkage between visual and auditory perception of space.
To quote American author E.A. Bucchianeri, “If you are what you eat, [then] you are what you see….”
Deborah Zelinsky, O.D., is a Chicago optometrist who founded the Mind-Eye Connection, now known as the Mind-Eye Institute. She is a clinician and brain researcher with a mission of building better brains by changing the concept of eye examinations into brain evaluations. For the past three decades, her research has been dedicated to interactions between the eyes and ears, bringing 21st-century research into optometry, thus bridging the gap between neuroscience and eye care. www.mindeye.com/tbiquiz