- Extensive use of screens—computers, mobile phones, and televisions—reduces the eyes’ ability to detect contrast in visuals.
- Lutein, an eye-protective antioxidant protects and improves the eye’s contrast sensitivity.
Contrast sensitivity is the ability of the eyes to tell an object from its background by identifying brightness and colour shades.
People with poor contrast sensitivity see high-contrast images as if they are hazy. The images below show poor contrast on the left and normal contrast on the right.
Reduced contrast sensitivity can hamper the quality of life:
- It can cause difficulty in driving, especially in rain or fog.
- You may not be able to spot dark objects against dark backgrounds (brown purse kept on a dark-coloured sofa) or bright objects against bright backgrounds (white plate kept on a white tabletop).
- Situations such as climbing stairs or walking on potholed roads, where contrast offers cues, become problematic.
Lutein and Zeaxanthin
- Lutein and zeaxanthin are potent antioxidants that protect the eyes from degenerative damage.
- Both are similar in structure and the body can convert either into the other. So we’ll refer to them together as lutein in this article.
- Lutein is stored in the central part of our retina.
- It is yellow in colour and so absorbs blue rays from any light falling on the retina.
- Our bodies cannot make lutein.
- It has to be obtained from food sources such as green leafy vegetables (spinach, peas, lettuce), and egg yolks.
Computer, Mobile Phone, and Television Use
More than five hours a day of use of modern screens (computers, mobile phones, tablets, and television) has been found to increase physical, mental and sleep-related symptoms.
In young adults, extensive use of screens reduces contrast sensitivity by three mechanisms:
Blue Rays Cause Retinal Damage
- Blue rays have high energy and when they fall on your retina, they jolt its delicate cells. This is light-induced oxidative stress and if it continues over a prolonged period, some of those cells start dying, reducing the contrast sensitivity permanently.
- This damage takes time to accumulate and be noticed. So this is one mechanism for ageing-related loss in contrast sensitivity.
- Extensive use of screens can accelerate this process and the symptoms may be seen at a young age.
- Lutein, by absorbing ninety per cent of the power of blue rays, protects against such reduction in contrast sensitivity.
- However, once the damage is done, nothing can be done to reverse it; you can only prevent worsening.
Blue Rays Scatter Inside Eyeballs
- When the light rays enter the eyeball, some get scattered. This is like shining a torchlight on a wall—some rays bounce off in random directions brightening a zone wider than the actual beam of light.
- The blue rays, being of the highest frequency, scatter the most. This results in our eyes perceiving lesser contrast in the visuals, especially in bright lights.
- Lutein absorbs most of the blue rays, leaving much less behind to be scattered and improving contrast sensitivity.
Unnecessary Stimulation in Low Light
- In our eyes, there are low-light sensing cells called rods. They are useful in low-light conditions such as night vision and play no role when one sees vivid colours in bright lights.
- But in the mid-range (dull, less-bright colours), they are stimulated a bit, sending signals to the brain that add no value to its understanding of the image.
- Lutein absorbs rays like those stimulating rods in such lights, increasing the contrast ‘seen’ by the brain in less-than-bright conditions.
- A rough example will be to think of two adjacent colour signals coming to the brain as light intensities of 50 and 40. If lutein removes the rod stimulus of 10 from each, the new colour signals will be 40 and 30, respectively. The contrast ratio of 50/40 = 1.25 is less than 40/30 = 1.33, making the latter difference easier to detect. Don’t focus on the numbers; get a flavour of the mechanism.
How Much Lutein Should You Take?
- Take 20 mg of lutein a day if you use computers or mobile phones for more than five hours a day.
- Two cups or 150 grams of spinach, kale, turnips, or collards a day will give you 20 mg of lutein.
- Lutein in fruits and vegetables is bound rigidly in the plant fibres. It needs to be released from the fibrous mass for better absorption in the intestines. Cutting and cooking such vegetables can improve lutein absorption.
- Egg yolk has thirty to fifty times less lutein than that spinach and kale. However, it is far more easily absorbable in the intestines, making egg yolk an excellent source of lutein.
- Lutein is a fat-soluble compound and is better absorbed if consumed with fats. Even a few grams of fat can increase lutein absorption in the intestines. The simplest way would be to eat your lutein-containing foods with a regular meal.
- Lutein supplements are convenient for people who may not be eating adequate amounts of colourful or leafy vegetables. A typical supplement tablet contains 5 mg of lutein and 1 mg of zeaxanthin. Take three a day with meals.
To Read More
- WebMD: What Are Contrast Sensitivity Issues With Vision?
- American Optometric Association: Computer Vision Syndrome
- MKRGEO: The role of contrast in ability of human vision
- On this Website: Lutein: A complete guide
- On this Website: Blue rays: How to protect eyes from this new threat
First Published on: 23rd May 2023
Image Credit: Chait Goli on Pexels