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There has been intense focus recently on the role of nutrients on age-related changes to ocular tissues. The Age-Related Eye Disease Study (AREDS) and subsequent AREDS2 were designed to assess the effects of oral supplementation of a variety of nutrients on the development of age-related macular degeneration and cataract. The nutrients studied included vitamin C, vitamin E, beta-carotene, zinc, lutein, zeaxanthin and omega-3 fatty acids. While the AREDS and AREDS2 results demonstrated that combinations of these nutrients appear to reduce the risk of advanced AMD, there remained questions about what effect these nutrients have on younger, healthy eyes.
Carotenoids are a type of pigment that can be found in certain vegetables and fruits.1 The body accumulates carotenoids in very specific anatomic structures. Lutein (L) and zeaxanthin (Z) are plant-derived carotenoids that are found to be concentrated in the eye and brain. While L and Z can be found in many tissues, they are found in highest concentrations in the macula, and have come to be known as the macular pigments. L and Z are concentrated within the inner layers of the fovea, specifically at Henle’s fiber layer, and acts as a filter for light.2,3
The macular pigments have peak absorbance for short-wavelength light (400-500 nm), and filters light before it reaches the cone photoreceptors. The peak energy of both blue haze and sky light is 460 nm, which coincides with the peak absorbance of the macular pigments (Figure 1).4 The absorption properties of L and Z are similar to that found with yellow-tinted filters, commonly referred to as “blue-blockers.” Therefore, the density of macular pigment is expected to have effects on visual performance factors, especially in natural sunlight.
VISUAL PERFORMANCE EFFECTS OF MACULAR PIGMENT DENSITY
There is mounting evidence that the density of the macular pigment has an effect on glare disability and discomfort, photostress recovery, and contrast enhancement. Many daily activities are performed either outdoors or at indoor facilities with variable lighting conditions. These conditions can create intense glare from natural sunlight or inappropriate overhead lighting. Light that is in the short wavelength portion of the visible light spectrum can produce glare that is particularly disabling, uncomfortable, and exacerbate photostress.5 There is less discomfort reported from short-wavelength light in those with a higher concentration of macular pigment, as well as less glare disability.6,7 Supplementation with L and Z has shown an improvement in glare disability that was proportional to the level of macular pigment increase.7-9 The same trend can be seen with photostress recovery following exposure to bright light, and visual discomfort.8,9 The ability to perform optimally under intense glare conditions, such as driving, may be improved by increasing macular pigment density.
Contrast sensitivity measures the visual system’s ability to process spatial or temporal information about objects and their backgrounds under varying lighting conditions. There is ample evidence that filters can have a positive effect on contrast discrimination, as well as reduce photostress recovery and glare disability. Recent research has demonstrated a linear relationship between macular pigment density and contrast enhancement.10 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.11 Therefore the ability to detect a target such as a baseball or tennis ball against a blue sky is enhanced with increasing macular pigment.
NEURAL EFFECTS OF LUTEIN AND ZEAXANTHIN
While the presence of L and Z in the macula is well recognized, these carotenoids also concentrate in the brain. Studies have shown that macular pigment density is linked to L and Z levels in the brain,12 and the level present is related to functions such as cognition, reaction time, and temporal visual processing. L and Z are incorporated in cell membranes and axonal projections, which serve to enhance interneuronal and neural-glial communication.13 Recently, supplementation with carotenoids has been shown to increase critical flicker frequency thresholds, visual motor reaction time, and temporal contrast sensitivity function compared to a placebo control group, improving processing speed by an average of 10% to 20%.14,15 In dynamic, reactive situations, this may enhance to 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.
VISUAL PERFORMANCE IN SPORTS
Athletes explore many options to improve performance. Training for strength, speed, agility, and cognitive skills have received significant attention over the years, while the athlete’s diet has gotten intermittent consideration. Dietary intake modifications have seen recommendations vary widely over the years. Most of the focus has been on diets designed to enhance muscle performance, particularly strength, endurance, replacement and recovery. Recent research has demonstrated that certain nutrients can improve visual performance factors.
Eye care professionals have several options to help athletes see their sport better. Recommendations can be made regarding amount of refraction compensation, method of refractive compensation, filters to enhance visibility of important information, and training to improve specific visual functions. Recommendations should also include modifications to diet to increase intake of carotenoids, or supplementation with purified forms of L and Z. Placebo-controlled studies have found that macular pigment density can be increased an average of about 20% with supplementation.6,7 For those athletes who experience difficulties with glare, photostress and contrast judgment, increasing macular pigment density offers a potential method to improve these functions by enriching natural physiology. Contrast sensitivity is important because most sports involve interpreting visual information at contrast levels below what is measured with a typical visual acuity chart. In addition, there are some athletes who 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. It may be that improvement in L and Z concentrations in the macula can provide enhanced visual function without the reduction in overall luminance that occurs with external filter use.
ATHLETES AND NUTRITION
Athletes often have very hectic schedules, and this can make it difficult to optimally manage dietary intake. Furthermore, many individuals prefer not to eat the types of fruits and vegetables that are rich in carotenoids (Figure 2).16,17 Poor dietary intake of L and Z from natural sources likely results in lower macular pigment density, which can be measured using customized heterochromatic flicker photometry. As mentioned earlier, supplementation with purified forms of these carotenoids for four months can improve macular pigment density, and maybe have much better compliance from athletes than dietary modifications alone. Recent studies have used 20 mg of dietary zeaxanthinin the supplements for those that are young and healthy, compared to concentrations for the aging population.8,14,15 In addition to the visual performance improvements found with supplementation, there is evidence that L and Z have protective effects for the retina from photooxidative damage.
Considering the evidence of the benefits from dietary intake of carotenoids, specifically L and Z, eye care professionals should consider recommending improved dietary intake to patients of all ages, especially athlete patients. For competitive athletes, care should be taken to recommend supplements that have been certified for content, including for substances banned in sports.19 For example, National Sanitation Foundation (NSF) International’s Certified for Sport program is widely recognized by major sports organizations. Supplements displaying the NSF Certified for Sport mark are confirmed to be free of the more than 180 banned substances by major athletic organizations. The mark also ensures that the content in the supplement actually matches what is printed on the label, the supplement does not contain an unsafe level of contaminants, and that the product is manufactured at a facility that is routinely audited by NSF for quality and safety. Nutritional counseling is another effective option to help athletes see their sport better. n
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2. Krinsky, NI, Landrum JT, Bone RA. Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye. Annual Rev Nutrition. 2003; 23:171–201.
3. Landrum JT, Bone RA. Lutein, zeaxanthin, and the macular pigment. Arch Biochem Biophys 2001;385:28–40.
5. Stringham JM, Fuld K, Wenzel AJ. Action spectrum for photophobia. J Opt Soc Am A Opt Image Sci Vis. 2003; 20:1852-1858.
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7. Stringham JM, Hammond BR. Macular pigment and visual performance under glare conditions. Optom Vis Sci. 2008; 85:82-88.
8. 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.
9. 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; 52:7406-415.
10. Renzi LM, Hammond BR. The effect of macular pigment on heterochromic luminance contrast. Exp Eye Res. 2010; 91:896-900.
11. Wooten BR, Hammond BR. Macular pigment: influences on visual acuity and visibility. Prog Retin Eye Res. 2002; 21:225-240.
12. 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.
13. Stahl W, Sies H. Effects of carotenoids and retinoids on gap junctional communication. Biofactors. 2001; 15:95-98.
14. 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. 2014; 9:e108178.
15. 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.
16. Ciulla TA, Curran-Celantano J, Cooper DA, et al. Macular pigment optical density in a midwestern sample. Ophthalmology. 2001; 108: 730-737.
17. Bernstein PS, Delori FC, Richer S, et al. The value of measurement of macular carotenoid pigment optical densities and distributions in age-related macular degeneration and other retinal disorders. Vision Research. 2010; 50:716-728.
18. Johnson EJ, Maras JE, Rasmussen HM, Tucker KL. Intake of lutein and zeaxanthin differ with age, sex, and ethnicity. J Am Diet Assoc. 2010;110:1357-1362.
19. NSF 306 Certification Guideline Certified for Sport. http://info.nsf.org/Certified/BannedSub/listings.asp. Accessed May 28, 2015.
Graham B. Erickson, OD, FAAO, FCOVD
• Professor, Pacific University College of Optometry, Forest Grove, Oregon
• (503) 352-3197; email@example.com