There are many unique features distinguishing the macula from other areas of the retina. Some of these include, but are not limited to, the density of cones, lack of retinal vasculature and presence of macular pigment. All these properties contribute to the macula’s ability to maintain the sharpest acuity for optimal vision. An often underthought contribution to ocular health and function is the presence of carotenoids in the macula, particularly of the lutein carotenoid. 

Lutein, along with its two stereoisomers—zeaxanthin and mesozeaxanthin—is the only carotenoid found in human tissue. This is a significant minority, since well over 800 types of carotenoids actually exist in nature through various microorganism and plant sources. The human body, however, does not have the ability to synthesize lutein on its own. Instead, it relies on dietary intake to fulfill its needs. To truly understand the function and benefit of lutein, it is necessary to evaluate its unique structure and biochemical properties.¹ 

Line of Defense

Lutein belongs to the carotenoid class known as xanthophylls; this class of carotenoid differs in structure from the carotene class. Unlike the carotenes, lutein possesses additional hydroxyl groups, allowing it to be a more polar and hydrophilic structure. As such, it can react with oxygen more readily, facilitating its antioxidant function—an integral part in maintenance of ocular health. Free radicals that may exist throughout the body and ocular structures contain an unpaired electron in their outer shell, making them susceptible to reacting with various molecules for stability and thus causing damage to these structures. Lutein interferes with this process by binding with free radicals which in turn eliminates their potential to bind to other structures.^1,2 

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Lutein also contains a particular liposomal cell membrane and is located in the highest density within the outer plexiform layer of the fovea. In addition to the macula, studies have found the presence of lutein in the crystalline lens. Because of these characteristics, lutein is the most effective blue-light blocker when compared with other carotenoids. This is of particular interest in the present day, as prolonged screen use from computers and phones has significantly increased individuals’ exposure to blue light. 

The effects of blue light on the eye are well documented and are known to increase the presence of free radicals, leading to macular damage and lens opacification. The peak wavelength of absorption of lutein is 460nm; this is within the range of blue light wavelengths. Subsequently, lutein has the potential to absorb 40% to 90% of these harmful rays, protecting the photoreceptors from their deleterious effects. As they reside in the lens as well, their protective properties extend there, too.³

Additional Benefits

In addition to these protective effects, studies have indicated that lutein also possesses anti-inflammatory properties against the agents of cyclooxygenase-2, inducible nitric oxide synthase and nuclear factor-kappa B. This is owed to lutein’s ability to prevent oxygen-induced cytokine formation as well as to upregulate inflammatory gene expression. Moreover, lutein has been able to reduce VEGF expression by reducing the inflammatory effects of ischemic disease.⁴ 

Finally, lutein has been shown to impact cellular apoptosis and increase glial cell function. Due to this observation, there is a suggestive potential for neuroprotective benefits derived from lutein. Additional evidence supports lutein’s role in improving visual and contrast acuities.⁴ 

Delivery Methods

Patient with dry age-related macular degeneration, one of the conditions lutein supplementation can benefit. Click image to enlarge.

Since the beneficial effects of lutein are many, it is paramount in maintaining ocular health. To procure it, though, it is necessarily acquired through external sources, as lutein is not synthesized by humans. Foods high in lutein include a wide variety of vegetables, grains, nuts and other sources. Leafy green vegetables, particularly kale, are excellent sources. Additionally, pistachios, certain types of wheat and egg yolk also contain lutein. 

Once lutein is ingested, it is absorbed via lipid droplets into the bloodstream for transport. Dietary fat allows for better absorption of carotenoids; this is due to lutein’s hydrophobic structure. In fact, it has been suggested that because lutein is distributed into adipose tissue, there is an inverse correlation between lutein levels and obese patients, increasing their susceptibility for ocular diseases.⁵

For clinicians, understanding the structure and biochemical properties of lutein gives us a clearer picture of the many benefits it poses—and the hazards that arise from deficiencies. We already know that lutein plays an integral role in treatment and management of age-related macular degeneration, but it can potentially benefit many other ocular conditions as well, such as diabetic retinopathy, retinopathy of prematurity, myopia and cataract. Further studies are ongoing and will likely impact future treatments.⁶

Dr. Labib graduated from Pennsylvania College of Optometry, where she now works as an associate professor. She completed her residency in primary care/ocular disease and is a fellow of the American Academy of Optometry and a diplomate in the Comprehensive Eye Care section. She has no financial interests to disclose.