Welcome to question of the day #121

Eyetools question of the day #121

I’ve spent most of my research life working on the macula lutea. It is also known as macular pigment and when measured it is called macular pigment optical density. I’ve measured it, I’ve tested the equipment that is marketed as measuring it, I’ve philosophized about it and I’ve written about it in books, clinical articles and peer-reviewed journal articles. All this is despite the fact that at optometry school it took up one sentence in my studies. The macular lutea is yellow, is at the centre of the macula and it is a pigment. That was it. My curiosity was satisfied which is probably why I went onto study it in more detail.

The term macula lutea comes from Latin macula, ‘spot’, and lutea, ‘yellow’. Macular pigment is found throughout the macula but is concentrated in the foveal area.

As the pigment is yellow it is very good at absorbing blue light from the short-wavelength part of the spectrum of natural light. Blue light is thought to be part of the cause of age-related macular degeneration. The pigment is made of lutein and two other hydrocarbons which are very good at neutralising harmful chemicals which are produced in the retina through the chemical and photic processes which occur in the process of seeing. The yellow pigment is also thought to play a role in visual acuity. Blue light may degrade visual acuity so having a yellow filter in the retina could help.

However, as early humans didn’t live into old age (mostly) why did a yellow pigment develop in the retina to prevent an eye condition which develops in old age? Evolution is usually not so wasteful. There is plenty of research linking high levels of macular pigment to a reduced chance of developing and very little linking it to visual acuity refinement. In my opinion, macular pigment is about visual acuity and the link with age-related macular degeneration is coincidental.

Macular pigment is difficult to measure but easier (probably) to build up. Kale contains lots of this pigment. Kale is a green, leafy, cruciferous vegetable that is rich in nutrients. It is a member of the mustard, or Brassicaceae, family, as are cabbage and Brussels sprouts. See figure.

As well as having the potential to increase levels of macular pigment other possible benefits include helping manage blood pressure, boosting digestive health, and protecting against cancer and type 2 diabetes.

However, it should be washed thoroughly before using as it is often treated with pesticides. Also, people taking beta-blockers for heart disease or who have kidney disease or who are taking blood thinners should consult their physician before consuming large amounts of kale. High levels of potassium and vitamin K can cause problems under these circumstances.