In our last post, Dr. Graham Erickson reviewed a few training techniques to improve sports vision. In part three of the series, he reviews another technique that’s less about training and more about eating: nutrition.
Dietary nutrients accumulate in the tissues of the eye and visual pathway in a manner similar to other tissues in the body. There are several nutrients that are beneficial for eye health and function, including vitamins A, C, and E, omega-3 fatty acids, beta carotene, zinc, selenium, lutein, and zeaxanthin. Vitamins A, C, and E, zinc, selenium, and lutein provide protective effects for age-related changes to the crystalline lens and retina (e.g. cataracts & AMD). Nutrients containing omega-3 fatty acids can reduce dry eye effects, and other nutrients protect the retina from sun damage (lutein, zeaxanthin, and beta carotene).
There has been significant research on the effects of nutrients on visual performance in young, healthy people. Lutein (L) and zeaxanthin (Z) are plant-derived carotenoids that are found to be concentrated in the eye and brain, and they were first noted in the macular pigment in 1985. L & Z are the only two naturally occurring carotenoids found in the macula and concentrated within the inner layers of the primate fovea, specifically at Henle’s fiber layer and act as a filter for light. Since the dietary intake of important nutrients is a modifiable factor, there is compelling evidence that increasing the intake of Z & L may provide important improvements to visual function that can benefit athletes.
There is mounting evidence from placebo-controlled, double-blind trials that the density of the macular pigment influences glare disability and discomfort, photostress recovery, and contrast sensitivity. Less discomfort is reported from short-wavelength light in those with a higher concentration of macular pigment, as well as less glare disability.1,2 Supplementation with L & Z has shown a reduction in glare disability that was proportional to the increase in macular pigment optical density (MPOD).2-4 The same trend can be seen with photostress recovery following exposure to bright light, and visual discomfort.3,4 The ability to perform under intense glare conditions may be improved by increasing MPOD.
Glare Recovery & Discomfort
Visible light is responsible for glare that can cause significant interference with an athlete’s ability to see the visual details critical for successful performance. For example, direct glare from the sun is evident in a blue sky because it affects the visibility of a lofted ball. For those athletes competing under artificial lighting during night games or indoor sports, the high-intensity light sources used for these purposes can also cause a significant amount of direct glare when an athlete must look toward the light source to track a ball or other object.
Reflected glare is exceptionally troubling for athletes when the sun is reflected off surfaces such as water, snow, pavement, and sand. These surfaces reflect horizontally polarized light that can produce substantial glare, particularly water surfaces that are constantly moving. Glare sensitivity and slow glare recovery may contribute to errors in certain sport conditions. In these cases, higher MPOD may help athletes experience less glare discomfort and better visibility under glare conditions.
There are also many sports situations that require the athlete to recover visual function quickly from intense glare. Slow visual recovery after looking toward the sun or arena lighting, or reflected from surfaces, can result in performance errors. These errors may put the athlete at risk of injury, such as in cycling sports or downhill skiing. Some sports situations require the athlete to move quickly between areas of bright sunlight and shadow, and quicker visual recovery offers a potential performance advantage. In baseball, half of the field can be shaded at times, while the other half is sunlit. Outfielders are forced to run in and out of the shaded areas, and their eyes are forced to adjust accordingly. Higher levels of macular pigment may improve their ability to recover in these situations and make the play. For everyday life, improved MPOD can aid a driver’s ability to see when moving into and out of tunnels, when driving toward the sun when it’s low in the sky, or recovering from the glare of oncoming headlights when driving at night.5
Recent research has also demonstrated a relationship between macular pigment density and contrast enhancement.6 Since the macular pigments selectively filter short-wavelength light, it has been proposed that those with a higher density of macular pigments have an expanded visible range (approximately 30%) due to the preponderance of short-wavelength light in the atmosphere.7 Therefore the ability to detect a target such as a baseball or a tennis ball against a blue sky is enhanced with increasing macular pigment.
While the presence of L & Z in the macula is well recognized, these carotenoids also concentrate in the brain. Randomized, double-masked, placebo-controlled trials of young healthy subjects have shown that MPOD is linked to L & Z levels in the brain,8 and the level present is related to functions such as cognition, reaction time, and the speed of visual processing.9-12 Neuroimaging to measure the relation of L & Z to brain structure has confirmed that L & Z influences white matter integrity, particularly in regions vulnerable to age-related decline.13 L & Z are incorporated in cell membranes and axonal projections, which serve to enhance interneuronal and neural-glial communication.14 This basically means that L & Z can help improve communication between brain cells.
Along with inter-cell communication, supplementation with carotenoids has also been shown to increase critical flicker frequency thresholds, visual-motor reaction time, and temporal contrast sensitivity function compared to a placebo group, improving processing speed by an average of 10% to 20%.10,11 In dynamic, reactive situations, this may enhance the ability to evaluate critical visual information faster. For example, more rapid visual processing allows a baseball batter to process more visual information regarding the judgment of the speed and trajectory of a pitched ball.
To help athletes achieve optimal visual performance, recommendations should include modifications to diet to increase the intake of carotenoids or supplementation with purified forms of L & Z. Placebo-controlled studies have found that MPOD can be increased an average of about 20% with supplementation.1,2 Some studies used 20 mg of dietary zeaxanthin in the supplements for those that are young and healthy, compared to lower concentrations for the aging population (the AREDS 2 formula has only 2 mg of zeaxanthin).5,10,11
For competitive athletes, care should be taken to recommend supplements that have been certified for content, including for substances banned in sports. Currently, the only available supplements that are formulated specifically for athletes are EyePromise Vizual Edge products and EyePromise Screen Shield Pro and Vizion Edge, which are National Science Foundation (NSF) Certified for Sport. In addition to the visual performance improvements found with supplementation, evidence exists that L &Z have protective effects for the retina from photo-oxidative damage. In addition to the protective effects of accumulated sun exposure over time in athletes, many also spend a considerable amount of time gaming. The protective effects of MPOD may also help with blue light exposure from extensive screen time.
Increasing MPOD offers a potential method to improve difficulties with glare, photostress, and contrast judgment by enriching natural physiology. Some athletes do not see a benefit from filter recommendations to help with glare disability, and filters can be cumbersome to change when moving between bright light and shadow. Improvement in L & Z concentrations in the macula can provide enhanced visual function without the reduction in overall luminance that occurs with external filter use. Further, common symptoms following traumatic brain injury include increased sensitivity to bright light (glare discomfort), glare disability, and slowed photostress recovery. Supplementation with L & Z may provide similar benefits to filter application in athletes who have concussion-related symptoms and may provide more long-term relief.
Athletes should be counseled on the time course for the effects of supplementation. The protective effects of L & Z are fairly immediate, but the visual and neural benefits will take longer for the macular pigment to accumulate. As a general guide, the visual benefits will take one to two months, and the neural benefits will need three to four months to become noticeable.
Get a recap of all the posts in this series here.
Graham Erickson, OD, FAAO, FCOVD has been on the faculty of Pacific University since 1998 and currently teaches the Vision Therapy, Strabismus/Amblyopia, and Sports Vision courses. He has authored the text Sports Vision: Vision Care for the Enhancement of SportsPerformance, as well as co-authoring the text Optometric Management of Reading Dysfunction, and published chapters and articles in various optometric journals. He lectures internationally on the topics of sports vision, pediatrics, and binocular vision.
Dr. Erickson published a perspective piece related to nutrition and visual performance in Vision Development & Rehabilitation. Find it on page 221.
- Stringham JM, Hammond BR. The glare hypothesis for macular pigment function. Optom Vis Sci. 2007; 84:859-864.
- Stringham JM, Hammond BR. Macular pigment and visual performance under glare conditions. Optom Vis Sci. 2008; 85:82-88.
- Hammond BR, Fletcher LM, Roos F, et al. A double-blind, placebo-controlled study on the effects of lutein and zeaxanthin on photostress recovery, glare disability, and chromatic contrast. Invest Ophthalmol Vis Sci 2014; 55:8583-8589.
- Stringham JN, Garcia PV, Smith PA, et al. Macular pigment and visual performance in glare: benefits for photostress recovery, disability glare, and visual discomfort. Invest Ophthalmol Vis Sci. 2011; 52:7406-15.
- Richer S, Park D-W, Epstein R, et al. Macular re-pigmentation enhances driving vision in elderly adult males with macular degeneration. J CLin Exp Ophthalmol 2012; 3:217.
- Renzi LM, Hammond BR. The effect of macular pigment on heterochromic luminance contrast. Exp Eye Res 2010A; 91:896-900.
- Wooten BR, Hammond BR. Macular pigment: influences on visual acuity and visibility. Prog Retin Eye Res. 2002; 21:225-40.
- Vishwanathan R, Neuringer M, Snodderly DM, et al. Macular lutein and zeaxanthin are related to brain lutein and zeaxanthin in primates. Nutr Neurosci 2013; 16:21–29.
- Renzi-Hammond LM, Bovier ER, Fletcher LM, et al. Effects of a lutein and zeaxanthin intervention on cognitive function: a randomized, double-masked, placebo-controlled trial of younger healthy adults. Nutrients 2017; 9:1246-59. doi:10.3390/nu9111246
- Bovier ER, Renzi LM, Hammond BR. A double-blind, placebo-controlled study on the effects of lutein and zeaxanthin on neural processing speed and efficiency. PLoS ONE 9 2014; 9:e108178.
- Bovier ER, Hammond BR. A randomized placebo-controlled study on the effects of lutein and zeaxanthin on visual processing speed in young healthy subjects. Arch Biochem Biophys. 2015;15(572):54-57.
- Stringham NT, Holmes PV, Stringham JM. Effects of macular xanthophyll supplementation on brain-derived neurotrophic factor, pro-inflammatory cytokines, and cognitive performance. Physiol Behav 2019; 211:112650.
- Mewborn CM, Terry DP, Renzi-Hammond LM, et al. Relation of retinal and serum lutein and zeaxanthin to white matter integrity in older adults: a diffusion tensor imaging study. Archives of Clinical Neuropsychology 2017; Nov 17:1–14. doi: 10.1093/acn/acx109. [Epub ahead of print]
- Stahl W, Sies H. Effects of carotenoids and retinoids on gap junctional communication. Biofactors. 2001; 15:95–8.