A new study may help identify exactly who is in most danger, and precisely what they should eat to ward off sight loss.
Blue and green eyes contain less of a substance called ‘macular pigment’, which is thought to protect against one of the leading causes of sight loss in the western world - age-related macular degeneration (AMD).
It affects more than 10% of Scots over the age of 80, and by 2020 it is predicted that about 750,000 people in Scotland will have the condition.
It occurs when part of the retina called the macula, which is at the centre of a person’s vision, degenerates over time, destroying central vision. There is no cure and current treatment relies on slowing down the progress of the disease.
It is thought that the more macular pigment in the eye, the more protected the macula is against deterioration.
Brown eyes tend to contain more of the pigment than blue and green ones, although it is not known why.
Scientists also think levels of macular pigment can be affected by diet, since the pigment’s main components are found in some vegetables and are concentrated by the eye. Dark green leaves such as kale, spinach and cabbage are among the richest sources.
A team from Heriot-Watt University and Edinburgh’s Princess Alexandra Eye Pavilion is studying about 100 volunteers of different ages to find out more. Subjects have their pigment level checked and are asked to record everything they eat and drink over a week.
As they get older, it is hoped they can be followed up to see if they develop AMD.
The information should help show the exact relationship between eye colour, eye pigment levels and diet.
By including other factors thought to be involved in AMD, such as a possible genetic trigger and the influence of smoking, it may be possible to predict an individual’s risk of getting the disease
and the best combination of foods to eat to maximise levels of the protective pigment.
The three main researchers have expertise in different areas. Baljean Dhillon is an eye surgeon at the Eye Pavilion and an AMD expert, while Peter Aspinall and Adrian Hill specialise in the science of vision.
Dhillon said: "Having light-coloured eyes - blue or green - tends to mean that you have less macular pigment, although we don’t really know why.
"That, in turn, seems to increase the risk of developing AMD. What we want to know is exactly who is most at risk and what can be done about it."
He said it might in future be possible to offer checks in the community, such as in opticians’ shops, which will rapidly quantify risk according to the exact shade of eye colour.
Peter Aspinall, professor of environmental studies at Heriot-Watt, said: "As yet there’s no known treatment to reverse AMD, so the best way is to prevent it. We think that two risk factors may be the amount of pigmentation naturally occurring in the eye, and dietary elements. There is already evidence that diet has a bearing on the density of pigment in the eye.
"One suggestion is that this pigment can screen out some of the harmful light rays that hit the eye, so the greater the density, the more effective it is at screening."
About 40 volunteers have so far been tested at the Eye Pavilion and it is hoped the rest will be seen over the next six months.