How does undernutrition affect eye health?

Undernutrition refers to an absence of energy-forming macronutrients and micronutrients from the diet, usually over a longer term, leading to a range of health problems, including chronic infections, growth deficits and other developmental problems ^[1].

Child undernutrition is a major cause of eye problems, mainly due to an absence of important micronutrients, as described in more detail below. The eyes need micronutrients daily, because they are highly active, both during waking and sleeping hours, and have a constant requirement for nutrient supply.

The main function of the eye is vision. Although this process happens automatically from birth, and gradually increases in its ability to recognize more complex information, performing this task requires lots of complicated systems working together. The main working parts of the eye are the lens, which focuses images, and the retina, a multi-layered structure that puts together those images and sends them via a nerve to the brain.

The main nutrient consuming parts of the eye are the more active parts that include:

• The retina (light detection)
• The muscles controlling the lens (focusing and sharpening light images)
• The eye lid muscles (protecting the outer eye parts)
• Glands that supply eye fluids (protecting and lubricating the eye)

These are supported by a special network of blood vessels that deliver oxygen and nutrients to keep these systems working effectively. We can also include the optical part of the brain, to which the retina is directly “wired in”, and is one of the most active parts of the brain – only 2% of the body, but using about 20% of its energy! ^[2].

Among the most critical nutrients is vitamin A, or “retinol”, which gets its name from its utilization for light sensing mechanisms in the retina. Vitamin A deficiency in children is one of the leading causes of blindness globally ^[2], and leads to dry eyes and vision spots. This is also referred to as “blinding malnutrition”^[3].

Another essential micronutrient is the omega-3 fatty acid group. Studies in infants and children have shown that levels of these fats, especially of DHA, are associated with improved visual acuity (sharpness) ^[4] . DHA works together with retinol in controlling how the retina senses light.

Lutein is in a similar class of nutrients to vitamin A, and like this vitamin, it can accumulate in the retina of infants and children ^[5]. There, it protects the macula, a small part of retina used for sharper image focusing. Lutein has been shown to improve low-light sensitivity in infants ^[6].

Other important micronutrients that are involved in the working of the retina include copper, manganese, zinc, B-vitamins and vitamin E. Some of these are involved in protecting it from light damage, which results in a process called oxidative stress, and why they are called “antioxidant” vitamins. Oxidative stress is higher in children who are ill or nutritionally compromised.

Luckily, nutrient related eye problems are generally reversible, provided the damage is not so bad that it becomes permanent. This is more likely when children’s diet lacks enough vitamin A and other micronutrients. However, eye problems are increasingly being reported in children with over-nutrition as well ^[8], so it is important the nutrient supply is a balance of macronutrients and micronutrients.