The eyes provide important clues to health status and are often used diagnostically in complementary and alternative medicine. Iridologists, for example, examine the eye to discover key information about which systems in the body may be under stress and require further support, and the latest scientific advances suggests a novel use for measuring pupil dilation and constriction to gain a better understanding of the autonomic nervous system, a key player in stress activation. Not only is the eye able to offer meaningful clues for health status, research suggests that specific nutritional deficiencies may play a role in the development of eye disorders, with some nutrients potentially reducing the rate of disease occurring altogether. Given that a large concentration of the body’s nutrient stores are in the eye region, optimising serum levels should be considered for maintenance of optimal vision. 

In order to understand the importance of nutrition for eye health it is important to understand the many different complex structures which work to provide vision. The lens receives light and sends this to the retina which is found at the back of the eye. The lens controls the amount of light it receives by constricting or dilating the pupil via the iris, the section that defines your eye colour. The cornea helps to focus vision. The retina contains a large concentration of photoreceptor cells in the macula, to support the brain with image formation. The cells of the retina and macula convert the light signals to the brain via the optic nerve. Whilst the macula provides an image, the retina provides peripheral vision. Finally, the sclera is the white part of the eye covered by the conjuctiva, a mucus membrane which helps to keep the eye lubricated. 

Vision is often taken for granted, with reduced visual abilities considered a normal part of the ageing process. When we consider ageing, health becomes compromised due to depletion in antioxidant capacity within the body, leaving repair systems compromised. (1) This reduced antioxidant capacity is mirrored in retinal cells, with antioxidant stores also depleting with age. (2) Whilst the eye is subject to oxidative damage from the production of ROS as part of normal cellular processes, the body’s inbuilt antioxidant defences work to keep this oxidative damage in balance. However, the eye is also affected by external sources of oxidative damage, from dietary factors, exposure to light (UV and blue-light), and cigarette smoking. (2) The oxidative damage caused by the cumulative effect of these assaults, coupled with depleted antioxidant abilities, is linked to the development of cataracts and age-related macular degeneration (AMD). (1, 2) With a high level of polyunsaturated fatty acids in the retina, the eye is also susceptible to lipid peroxidation, which is also linked with AMD and cataracts, as well as glaucoma and diabetic retinopathy. (2, 3)

Smoking is linked with many health conditions; in terms of eye heath, this includes glaucoma, AMD and cataracts. (4-6) Whilst their exact role is unknown, cigarettes do contain chemical oxidants which induce oxidative damage, and deplete plasma levels of antioxidants including vitamin C, an important antioxidant for retinal health. (5, 6) Whilst many believe that vaping provides a solution to nicotine addiction, research is still lacking and with long-term effects still unknown.

Whilst the human eye has always been subject to light, the exposure has evolved in both the source and duration. Our ancestors were once exposed to light only from the sun and fire. These days, however, light is also sourced from fluorescent and LED lights, digital screens and electronic devices. While most choose to wear sunglasses to protect the eye from the sun’s harmful UV rays, not much protection is provided from the blue light emitted from technological sources. Blue light is particularly damaging as it has a shorter wavelength than the other visible colours, between 390nm and 500nm, which creates a flicker and can lead to glare; this may explain eye strain, headaches and fatigue from long-term exposure to screen time. Research suggests that blue light can lead to cellular damage and even cell death, making antioxidant defences essential to counteract their damaging effect. (1, 2, 7) Whilst blue light-blocking glasses are available to purchase, research is still limited regarding their viability as protection from macular disease. (8) Reducing screen time, using apps/settings to reduce blue light on screens, using non-fluorescent lighting and maximising antioxidant levels may be more viable options for protection from blue light.

Whilst many may have been persuaded of the benefits of eating carrots to help with night vision during childhood, the link between nutrition and eye health often ends there. Given the significance of antioxidants in the protection against disease development and the role of key nutrients in eye health, efforts should be made to maximise nutrient stores.

Both the body and eyes require antioxidants to neutralise ROS. As the eye is highly susceptible to the damaging effects of ROS, the retina is rich in dietary antioxidants including vitamins C and E, and carotenoids lutein and zeaxanthin. (1)

1. Carotenoids 

Carotenoids are vitamin A pro-vitamins with antioxidant properties. Within the retina, they make up the pigments found in the yellow spot where they play several roles; they protect the macula from blue light damage, suppress the production of ROS and improve visual acuity. (2, 11)

Whilst carotenoids are present in human tissues, including skin and the eyes, they also provide the colour pigments in plants and are found in brightly coloured fruit and vegetables, with lutein and zeaxanthin more concentrated in green leafy vegetables and other green or yellow vegetables, with supplementation an option to top-up levels where the diet may fall short. 

With its potent antioxidant properties, the beta-carotenoid astaxanthin also protects the cells of the eye from light exposure, with four weeks of supplementation improving the function of the eye in those with eye strain complaints. (12, 13) 

2. Vitamins C & E 

Vitamin C is found in higher concentrations in the aqueous humor (fluid between the lens and the cornea) than in any other bodily fluid. (9) Increasing nutritional intake of vitamin C has been shown to increase plasma levels within the aqueous humor and therefore provides a viable option to increase vitamin C stores. (9) Dietary sources include citrus, kiwis, mangoes, tomatoes, peppers and broccoli; also useful is supplementation recommended for smokers, during pregnancy, and for those who do not achieve 7-a-day. 

The eye is rich in alpha- and gamma-tocopherols (types of vitamin E), with a high serum level linked to a reduced risk for cataracts. (9). Dietary sources include green leafy vegetables (with each serving providing 15-25% daily requirement), and healthy fats such as olives, avocados, nuts and seeds. 

This article is intended to provide an overview of the key nutrients required not only to support eye health but also prevent, or delay, the onset of eye pathology.

1. Saccà, S. C., Cutolo, C. A., Ferrari, D., Corazza, P., & Traverso, C. E. (2018). ‘The Eye, Oxidative Damage and Polyunsaturated Fatty Acids’. Nutrients, 10(6), 668. doi:10.3390/nu10060668
2. Rohowetz, L. J., Kraus, J. G., & Koulen, P. (2018). ‘Reactive Oxygen Species-Mediated Damage of Retinal Neurons: Drug Development Targets for Therapies of Chronic Neurodegeneration of the Retina’. International journal of molecular science. 19 (11), 3362. 
   
3. Gong, Y., Fu, Z., Liegl, R., Chen, J., Hellström, A., & Smith, L. E. (2017). ‘ω-3 and ω-6 long-chain PUFAs and their enzymatic metabolites in neovascular eye diseases’. The American journal of clinical nutrition, 106(1), 16–26. doi:10.3945/ajcn.117.153825 
   
4. Sörensen, B. M., Houben, A. J. H. M., Berendschot, T. T. J. M. et al. (2017). ‘Cardiovascular risk factors as determinants of retinal and skin microvascular function: The Maastricht Study.’ PloS One, 12 (10). doi: 10.1371/journal.pone.0187324. 
   
5. Datta, S., Cano, M., Ebrahimi, K., et al. (2017). ‘The impact of oxidative stress and inflammation on RPE degeneration in non-neovascular AMD.’ Progress in retinal and eye research, 60, 201–218. doi:10.1016/j.preteyeres.2017.03.002 
   
6. Kang, J. H., Wu, J., Cho, E., et al. (2016). ‘Contribution of the Nurses' Health Study to the Epidemiology of Cataract, Age-Related Macular Degeneration, and Glaucoma.’ American journal of public health, 106(9), 1684–1689. doi:10.2105/AJPH.2016.303317
7. Kuse, Y., Ogawa, K., Tsuruma, K., et al. (2014) ‘Damage of photoreceptor-derived cells in culture induced by light emitting diode-derived blue light.’ Scientific reports, 4, pp. 5523. doi: 10.1038/srep05223 
   
8. Lawrenson, J.G., Hull, C.C., Downie, L.E., et al. (2017) ‘The effect of blue-light blocking spectacle lenses on visual performance, macular health and the sleep-wake cycle: a systematic review of the literature.’ Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians, 37, (6) pp. 644-654. 
   
9. Phelps Brown, N., A., Bron, A. J., Harding, J. J., Dewar, H. M. (1998) ‘Nutrition supplements and the eye’. Eye, 12, pp. 127-133. 
   
10. Datta, S., Cano, M., Ebrahimi, et al. (2017). ‘The impact of oxidative stress and inflammation on RPE degeneration in non-neovascular AMD.’ Progress in retinal and eye research, 60, 201–218. doi:10.1016/j.preteyeres.2017.03.002 
    
11. Guerin, M., Huntley, M. E. & Olaizola, M. (2003) ‘Haematococcus astaxanthin: applications for human health and nutrition.’ Trends in biotechnology, 21 (5), pp. 210-6.
    
12. Tomohiro O., Masamitsu S., Tomohiro N., et al. (2013). ‘The Protective Effects of a Dietary Carotenoid, Astaxanthin, Against Light-Induced Retinal Damage’, Journal of pharmacological sciences’, 123, pp. 209-218.
13. Kajita M., Tsukahara H. & Kato M. (2009). ‘The Effects of a Dietary Supplement Containing Astaxanthin on the accommodation Function of the Eye in Middle-aged and Older People’, Translated from medical consultation and new remedies, 46 (3), pp. 1-7.