Xanthophylls are a subclass of carotenoids, a large group of plant pigments responsible for the colors of bright fruits and vegetables. Although more than 600 carotenoids are found in nature, just 40 to 50 are consumed in the typical diet, and only 14 have been detected in serum.1 Of these 14, just lutein, zeaxanthin and their metabolites are located in the macula. Macular pigment (MP) serves as a filter that absorbs blue light and has been shown to act as a potent antioxidant, quashing free radicals associated with the pathogenesis of age-related macular degeneration (AMD).2

Lutein and zeaxanthin are found in egg yolk, yellow fruits and vegetables, and in dark green leafy vegetables like spinach, kale and collard greens. Low levels of lutein and zeaxanthin in the diet, serum or retina may result in an increased risk of AMD.2,3 Much of the early MP research—including supplementation studies—focused on lutein exclusively. More recent epidemiological evidence suggests that zeaxanthin may be of equal importance in protecting the fovea.3,4

Nutritional therapy with dietary and/or supplemental MP, along with other potentially beneficial agents (such as omega-3 fatty acids), is one means of proactive intervention. In our nutrition-based efforts to preserve patients’ macular health, we also may be enhancing their visual function.

Clinical Application of MPOD
The amount of MP in the retina can be quantified in a clinical setting. The most studied method is a psychophysical technique called heterochromatic flicker photometry (HFP), which uses flickering blue and green light targets to yield a measurement reported in density units as macular pigment optical density (MPOD). Lower MPOD can be associated with increased risk for AMD, as well as several other risk factors for AMD (including poor diet, smoking, low serum carotenoid concentration and high body mass index).5

The optometrist is an important resource for patients seeking to achieve optimum retinal health and protection. We start by advising patients to eat a balanced diet that is high in fish and whole grains, emphasizing fruits, vegetables (especially greens) and fat-free or low-fat dairy products.

Lutein and zeaxanthin have peak absorptions around 446nm and 451nm respectively, which is in the blue light range of the visible spectrum.
The diet should also include lean meats, poultry, beans, eggs and nuts. It should be low in saturated fats, trans fats, cholesterol, salt (sodium) and added sugars.6 A broad-spectrum multivitamin may be advisable for patients who are unable to achieve these dietary goals. Some multivitamin products contain lutein and zeaxanthin, in addition to other vitamins and minerals that are important in ocular health (such as vitamin C, vitamin E and zinc).

For patients at risk for AMD due to genetic, personal, systemic or environmental factors, or those who show early signs of the disease, we supplement with both zeaxanthin and lutein. First, we obtain a baseline MPOD measurement with heterochromatic flicker photometry. It is generally appropriate to administer a dosage of 4mg to 10mg of zeaxanthin per day, depending upon the patient’s diet (especially green vegetable intake), body mass, MPOD and other health factors.2,4

For lutein, 6mg to 20mg per day typically is suitable, again depending upon the various patient characteristics.3,4 We usually supplement for six months before rechecking the MPOD.

If you have questions about whether or not a vitamin supplement is appropriate for a particular patient, contact the patient’s primary care physician, pharmacist or a nutritionist before proceeding.

Improved Visual Function
A growing body of evidence suggests that the antioxidant and blue-light filtering properties of MP may be associated with improved visual function.3,7 Lutein and zeaxanthin may attenuate photophobia or discomfort associated with intense short-wavelength targets and may impact the threshold for photophobia under normal viewing conditions.3

Recent findings demonstrated that supplementation with lutein and zeaxanthin increased MPOD in a healthy population and led to an improved tolerance to glare and decreased photo-stress recovery time.3,7 Likely via its blue-light filtering property, MP contributes to better visual acuity, glare recovery and contrast sensitivity in healthy individuals as well as those with age-related eye diseases.8,9 High levels of MP additionally attenuate chromatic aberration and photophobia.10

The Zeaxanthin and Visual Function Study evaluated MPOD, visual acuity, contrast sensitivity, shape discrimination, color vision, glare recovery, central kinetic perimetry and lipofuscin pattern changes following supplementation with 9mg lutein, 8mg zeaxanthin or a combination of the two xanthophylls per day for 12 months.3

In the zeaxanthin group, high-contrast visual acuity improved by 8.5 letters/1.5 lines and foveal shape discrimination sharpened from 0.97 to 0.57.3 The zeaxanthin group had the largest percentage of subjects who had clearing of their kinetic visual field central scotomas. In addition, these patients reported an improvement in night driving skill.3

Numerous studies suggest that retinal lutein and zeaxanthin may protect the macula from light-induced damage.

The light-filtering properties of macular pigment also may influence visual comfort, function and performance. A patient’s MPOD can potentially serve as a biomarker not only for predicting the risk for eye disease, but also for visual function.

Stay tuned for Part 2 of this column, which will appear in the July 2012 issue. In that piece, we’ll discuss the role of macular pigments in systemic wellness.

Disclosure: Drs. Pelino and Pizzimenti have no proprietary interest in any instrument, food product, vitamin or supplement. Dr. Pizzimenti serves on the scientific advisory board for ZeaVision.

1. Khachik F, Beecher GR, Goli MB, et al. Separation and identification of carotenoids and their oxidation products in the extracts of human plasma. Anal Chem. 1992 Sep;64(18):2111-22.
2. Snodderly DM. Evidence for protection against age-related macular degeneration by carotenoids and antioxidant vitamins. Am J Clin Nutr. 1995 Dec;62(6 Suppl):1448S-61S.
3. Richer SP, Stiles W, Graham-Hoffman K, et al. Randomized, double-blind, placebo-controlled study of zeaxanthin and visual function in patients with atrophic age-related macular degeneration: the Zeaxanthin and Visual Function Study (ZVF) FDA IND #78, 973. Optometry. 2011 Nov;82(11):667-80.e6.
4. 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 Res. 2010 Mar 31;50(7):716-28.
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6. U.S. Department of Agriculture. MyPyramid.gov: Steps to a Healthier You. Available at: www.mypyramid.gov/index.html (accessed May 5, 2008).
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8. Bahrami H, Melia M, Dagnelie G. Lutein supplementation in retinitis pigmentosa: PC-based vision assessment in a randomized double-masked placebo-controlled clinical trial [NCT00029289]. BMC Ophthalmol. 2006 Jun 7;6(1):23.
9. Richer S, Stiles W, Statkute L, et al. Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial). Optometry. 2004 Apr;75(4):216-30.
10. Wenzel AJ, Fuld K, Stringham JM, Curran-Celentano J. Macular pigment optical density and photophobia light threshold. Vision Res. 2006 Dec;46(28):4615-22.