‘Stop reading in the dark or you’ll ruin your eyes!’ You may remember hearing this from your parents when you were curled up in bed as a kid with your torch and the book that you just couldn’t put down. Now, when you see other people or maybe even your own children reading away in dim light, you want to flip the light switch on or scold them in just the same way.
Dim light can certainly make you have difficulty focusing. It can also decrease how often you blink, making you uncomfortable because your eyes get dry and you squint for too long. However, the bottom line is that the effects of eye strain do not last. Once you return to good lighting, the effects go away.
There is simply no evidence proving that reading in the dark will ruin your eyesight for ever. In the face of no clear scientific evidence, we have to look at what other sources we can find – expert opinions, related studies and historical trends. The majority of ophthalmologists conclude that reading in dim light does not damage your eyes. Although reading in dim light can cause eye strain, with multiple temporary, negative effects, it is unlikely to cause a permanent change in the function or structure of the eyes.
One study did examine how the rate of blinking decreases during intense reading for patients with disorders that cause dry eyes, such as Sjogren’s Syndrome. For patients with this syndrome, the decreased blinking and eye strain during reading can result in a temporary decrease in how well they can see. However, even in people with this condition, visual acuity improved when the patients stopped reading, again suggesting that the eyes return to their normal baseline when the strain is removed.
On the other hand, one review article on short-sightedness does conclude that ‘increased visual experiences’, such as reading in dim light or holding books too close to the face, could result in ‘impaired ocular growth and refractive error’ (in other words, reading in dim light might ruin your eyes). The primary evidence cited to support this claim is that short-sightedness is becoming more and more common, and that people who read more are more likely to be short-sighted. The author notes that this hypothesis is just beginning to ‘gain scientific credence’.
In examining this argument, we must consider several important facts. First of all, association is not the same as causation. Just because more people who read a lot are short-sighted does not mean that the reading in dim light causes their short-sightedness. Even if the two are linked, the key factor may be the amount a person reads, not the amount of light present where the reading takes place. Another factor to consider is historical trends in lighting. Before the invention and widespread use of light bulbs, people had to rely on reading by candlelight in dark rooms. Now, most of us have access to light for reading whenever necessary. We have never had better light for reading in the history of the world. In that sense, the fact that more people are short-sighted today, when the world is so well lit, does not support the idea that reading in dim light hurts your eyes.
Thus our conclusion is that definitive scientific data do not exist to support or refute the claim that reading in dim light will ruin your eyesight, but the majority of experts believe (and common sense suggests) this is not true.