Have you ever questioned why our elders advise us to eat vegetables? Or why and how they are so crucial for our health - particularly that of our eyes? 

Read on to discover the answers to both of these questions. In this article, we describe the structure of the eye, talk about the importance of eye health, and address the role that vegetables have in maintaining eye health.

The structure of the eye

Vision is perhaps the most dominant yet complex sense for humans. The eye, the tissues surrounding it, and its connections to the brain are all incredibly intricate. The eyeball itself is a complex structure, with several other accessory structures that are essential for vision and movement of the eye.¹ 

The adult eyeball measures about 2.5 centimetres in diameter. It is supported by a wall which composed of three layers: the fibrous tunic (the outermost layer), the vascular tunic (the middle layer), and the retina (the innermost layer).^1,2 

• The fibrous tunic is composed of two structures known as the cornea and sclera, which protect structures inside the eye
• The vascular tunic consists of the choroid, ciliary body, and the iris. The choroid provides oxygen and nourishment to the eyeball, while the ciliary body contains small blood vessels called capillaries that secrete aqueous humour (clear liquid that provides nutrition helps the eye keep its shape). The iris (the coloured part of your eye) regulates the amount of light entering the eye through the pupil (the hole present in the iris)
• The retina consists of a pigmented layer and a neural layer, which together work to capture the light entering the eye and translate it into images that we can see. The retina contains photoreceptor (light-receiving) cells called rods and cones, which specialise in converting light rays into nerve impulses
• The lens of the eye is situated in a cavity behind the pupil and iris. Here, it is held in place by the ciliary muscles. The lens divides the eyeball into two halves: the anterior cavity (containing the clear aqueous humour) and the vitreous cavity (containing vitreous humour - another clear fluid that helps support the eye shape and shock absorbance)^1,2 

The importance of keeping good eye health

According to the Lancet Global Health Commission on Global Eye Health, eye health is defined as a state in which the vision, ocular health, and functional ability of the eyes of an individual are maximised, which thereby contributes to their overall health, social well-being, and quality of life.³ Therefore, good eye health is considered both a process leading to and an outcome of, the functional well-being of individuals. 

Good eye health is associated with several general health and well-being ‘Sustainable Development Goals’ (SDGs), including increased economic productivity, better prospects, household income, household spending, and workplace productivity.^4,5,6,7,8 Moreover, educational performance is closely associated with vision and overall eye health.^9,10,11 

Globally, vision impairment is one of the main causes of disability. In 2020, the Vision Loss Expert Group of the Global Burden of Disease Study (VLEG–GBD) estimated that 553 million people had difficulties with their distance vision, 510 million people had uncorrected near vision impairments, and 43 million people were blind.¹²

Moreover, most cases of vision impairment are related to preventable disorders, including cataracts and uncorrected refractive error. Impaired vision is linked to poor health outcomes, including the development of several chronic illnesses, higher mortality rates, significant socio-economic repercussions for the affected person, and a correspondingly reduced quality of life.³ 

Common eye health problems

The leading reasons for blindness and poor vision globally are primarily age-related eye diseases, such as age-related macular degeneration (AMD), cataracts, diabetic retinopathy, and glaucoma. Other common eye disorders include refractive errors: myopia (near-sightedness), hyperopia (farsightedness), astigmatism (distorted vision at all distances), and presbyopia (age-related farsightedness). Amblyopia, also referred to as “lazy eye,” is the most frequent eye disorder in children.¹³ 

Nutrients in vegetables: building blocks for healthy eyes

Sustaining and maintaining optimal eye health is essential for both our general health and visual abilities. Nutrition is a key factor in supporting and preserving our eye health, and among the diverse array of nutrient-rich foods available to us, vegetables are powerful guardians of our vision. In the next part of this article, we will explore the intricate relationship between vegetables and eye health, shedding light on the essential nutrients and compounds found in vegetables that contribute to optimal eye function.

Some of the nutrients found in vegetables that can significantly boost our eye health include: 

Carotenoids and xanthophylls

Lutein and zeaxanthin are two major carotenoids (natural plant pigments) that play pivotal roles in protecting eye health. They are abundant in green leafy vegetables such as kale, spinach, broccoli, peas, basil, parsley, leek, and lettuce, as well as egg yolks.

However, einkorn wheat, Khorasan wheat, durum wheat, and maize contain relatively high concentrations of carotenoids too. According to several reports, the ratio of lutein to zeaxanthin in green vegetables varies from 12 to 63, with kale having the greatest ratio. In yellow-orange fruits and vegetables such as yellow or red pepper and carrot, the ratio ranges from 0.1 to 1.4.^14,16,18

The protective mechanisms of lutein and zeaxanthin in eye health include:

Antioxidant properties

The human retina is particularly vulnerable to oxidative damage due to its high metabolic activity and near-constant exposure to short-wavelength visible light rays. Both metabolic reactions and light exposure can trigger the production of reactive oxygen species (ROS) and free radicals, which readily react with and damage lipid, protein and nucleic acids present in the eye. This damage can accumulate and eventually cause disease, such as age-related macular degeneration (AMD).

Carotenoids are able to neutralise reactive oxygen species and free radicals and prevent the peroxidation of molecules of the eye. Together, lutein and zeaxanthin help in protecting the eye from free radicals.^14,15,16 

Filters of blue light

Overexposure to light damages the retina and speeds up degeneration. Lutein and zeaxanthin protect the eye against harmful high-energy light waves by filtering out blue light, which is particularly damaging. Also, experts believe that carotenoids are able to block up to 40% of blue light before it reaches the macula.^15,16

Vitamins

Vegetables are a great source of antioxidants, which counteract free radicals that can damage eye cells. Vegetables like bell peppers, carrots, and sweet potatoes provide vitamins A, C, and E, which function as potent antioxidants, promote corneal health, and lower the incidence of cataracts and age-related macular degeneration.^16,18

Vitamin A

Vitamin A, and its by-product beta-carotene, play a crucial role in maintaining eye health. Vitamin A is essential for the normal vision of eyes, and vitamin A deficiency can significantly hamper the function of the eye’s rod and cone cells. Rod dysfunction results in night blindness (inability to see in the dark), whilst cone dysfunction impairs daytime vision. Vitamin A is abundant in red, orange, and yellow vegetables such as carrots, peppers, sweet potatoes, melons, and tomatoes. However, it can also be found in spinach, peas, parsley, pistachios, kale, broccoli, and Swiss chard.

In addition, studies have shown that consuming high levels of Vitamin A and provitamin A (β-carotene) decreases your risk for development of ocular diseases like AMD.^16,17,18

Vitamin C

Vitamin C, also known as ascorbic acid, is a potent antioxidant that protects proteins, lipids, carbohydrates, and nucleic acids against free radicals and reactive oxygen species (ROS). The beneficial effects of vitamin C include a reduced likelihood of neurovascular retinal diseases like AMD. In the eye, vitamin C may also be able to promote the regeneration of other antioxidants, such as vitamin E. Vegetables such as broccoli, brussels sprouts, cabbage, cantaloupe, cauliflower, green peppers, spinach, tomatoes are rich in vitamin C.^16,18

Vitamin E

The vitamin E family consists of eight members, with α-Tocopherol being the most actively maintained form in the human body. α-Tocopherol primarily functions as an antioxidant in humans, and protects fats from oxidative damage.

By extension, this prevents retinal damage. When α-tocopherol neutralises a free radical, it undergoes a change that results in the loss of its antioxidant ability. Luckily, other antioxidants, such as vitamin C, can restore α-tocopherol's antioxidant capacity.

As such, studies have shown that consuming more vitamin E increases concentrations of vitamin E in the retina and slows the progression of AMD. Vitamin E-rich foods include vegetable seeds and oils, such as almonds, peanuts, sunflower seeds, and oil, soybean oil, and corn oil.^16,18

Minerals

Among the essential minerals required by the body, zinc is essential for maintaining the health of the retina. Zinc acts as a cofactor for several important metabolic enzymes within the eye, and is therefore necessary for several processes including immunity, reproduction, and neural development. Furthermore, zinc is crucial for antioxidative processes and protecting structures and proteins within the eye. As such, zinc deficiency can cause the cell membranes of the eye to become much more susceptible to oxidative damage.

The vegetables with the highest concentration of zinc include spinach, mushrooms, asparagus, corn, broccoli, oats, garlic, and zucchini. Nuts and seeds from vegetables like pumpkin, sunflower, flax, chia, walnut, cashew, and almonds are also rich in zinc.^16,18

Omega-3 fatty acids

Alongside antioxidants, the omega-3 fatty acids DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) help prevent AMD. Omega-3 fatty acids provide several protective benefits in the retina, such as altering metabolic processes to minimise oxidative stress and reducing inflammation and vascularisation. Furthermore, experts suggest that atherosclerosis (blockage) of the blood vessels supplying blood to the retina may contribute to the risk of developing AMD.^16,18,19 

While fish and seafood tend to be higher in DHA and EPA type of Omega-3, vegetable sources such as seaweed, algae, chia seeds, flaxseeds, walnuts, kidney beans, and soybean oil are fortified with ALA (alpha-linolenic acid) omega-3 acids.¹⁸ 

Summary 

• Vision is an intricate vital sense, involving complex structures like the eyeball, accessory tissues, and visual circuits in the brain
• The eyeball has three layers: the fibrous membrane (cornea and sclera), the vascular membrane (choroid, ciliary body, iris), and the retina (pigment and neural layers with photoreceptors)
• The lens divides the eye into anterior and vitreous cavities containing aqueous and vitreous humour, respectively
• Good eye health is essential for overall health, which is linked to economic productivity, employment, income, and educational achievement
• Visual impairment, which is a major problem worldwide, affects millions of people’s health and quality of life - and is often preventable
• The nutrients found in vegetables can have vital roles in maintaining optimal eye health. The different nutrients to consider for excellent eye health include:
  • Carotenoids and xanthophylls: lutein and zeaxanthin, found in green leafy vegetables, protect the eye through antioxidant properties and filtering blue light
  • Vitamins A, C, and E: these vitamins are found in vegetables like bell peppers, carrots, and sweet potatoes, and act as antioxidants, promoting corneal health and reducing your risk of cataracts and AMD
  • Zinc: zinc is essential for retinal health, and can be found in vegetables like spinach, mushrooms, asparagus, as well as in various nuts and seeds
  • Omega-3 fatty acids: DHA and EPA, which are abundant in fish and seafood, and ALA, which can be found in seaweed, chia seeds, and walnuts, contribute to neuroprotection and prevent AMD
• In conclusion, vegetables play a crucial role in maintaining optimal eye health by providing essential nutrients. From carotenoids to vitamins A, C, E, minerals like zinc, and omega-3 fatty acids, each vegetable contributes uniquely to nourishing and preserving eyesight. Therefore, embracing a vegetable-rich diet is an investment in the longevity and vitality of our eyes