Q: Will reading in bad light ruin your eyesight?
The straight answer: No
As children, many of us were warned not to read in low light - for example, under our bedcovers with a flashlight - because it would damage our eyesight in the long term.
This belief is so widely accepted that even some health care professionals do not question it. But this idea is nothing more than a medical myth, and there is no strong evidence to support it.
The fact is, nature has its way of helping us navigate through dim lighting, and our eyes are designed to adjust to variations in light level.
When light is scarce, our iris muscles relax and our pupils dilate to take in more light onto our retinas, whereas in bright light, our pupils contract to minimise the amount entering our eyes.
Our retinas - networks of nerves that sit at the back of the eyes - contain light-sensitive cells called rods and cones. The rod cells help us to see when there is very little light present, while the cones help us with colour vision and detail in a well-lit situation.
When light hits our retinas, chemical signals are generated by the rods and cones and are then sent to the brain via the optic nerve.
Reading without sufficient light may not damage your vision, but it can cause eyestrain. That is because the muscles that control the shape of the lens have to work harder to focus on what you are reading. The muscles have to stay contracted to keep this focused image on our retinas.
If this squinting carries on for a stretch of time, our eye muscles can become fatigued, and there may even be accompanying headaches, neck strain, blurred vision, and eye dryness. (Blinking helps to lubricate the eye, but when we try hard to focus, we may not blink enough.)
These symptoms are temporary. This is why health experts advise us to rest our eyes every 15 minutes when reading, studying, watching television, or doing computer work for an extended period of time.
The link between close eye-work, such as sewing, and myopia (short sightedness) is interesting.
Myopia rates are also high in populations where people spend long hours reading and studying - such as in some parts of East and Southeast Asia.
Myopia is thought to be caused by a combination of factors such as birth weight, genetic predisposition, and diet but it is also known that focusing on close objects contracts the muscles that control the shape of the eye's lens.
When this contraction is prolonged, the eyeball may stretch, encouraging myopia.
Close eye-work and reading in dim light might involve contraction of the same eye muscles but so far no solid studies have been done to prove that poor lighting impairs vision.